Negative 48 Volts DC

[Grant Taylor]

Is anyone willing to explain Negative 48 Volts DC?

I'm trying to learn about it because we're using it for a few things at
work (servers and switch equipment) and I'd like to better understand
what we're working with than simply going through the motions that
someone else dictates. Read: I want to understand and not simply rely
on wrote memory.

I've learned that -48 VDC uses what is called "Positive Ground" and that
what I'm used to is called "Negative Ground".

I'm trying to correlate and understand the typical red and black wires
with them being ground / return / common / hot / etc.

I suspect that there is more to it than simply reversing the + and -
lead from a battery or meter. But I can't wrap my head around it.

Can ~> will someone offer any comments that might help me understand
better?



--
Grant. . . .
unix || die

[George Herold]

Right, Say you have a 48V battery.
You hook up the neg. terminal to ground, you've got +48V at the
positive terminal.
You hook up the pos. terminal to ground and it's -48V at the negative
terminal.

George H.

[Rick C]

On Saturday, January 25, 2020 at 2:21:25 PM UTC-5, Grant Taylor wrote:

I'm at a loss to understand what you are confused about. Do you have any specific questions???

How does any of this impact using the 48 volts to supply the equipment you list? In other words, why are you confused?

--

Rick C.

- Get 1,000 miles of free Supercharging
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[Jeff Liebermann]

On Sat, 25 Jan 2020 12:21:25 -0700, Grant Taylor
<gta...@tnetconsulting.net> wrote:

>Is anyone willing to explain Negative 48 Volts DC?

Sure. It goes back to telegraphy and telephony. The power to run the
telegraphs and telephones came from batteries. One terminal of the
battery went to earth ground. The other terminal went to the wires
between stations. The problem was, which is better? Positive ground
or negative ground.

It was decided to use positive ground. The battery positive terminal
went to ground, while the negative terminal went to the stations and
wires resulting in a -48VDC system. The selection of polarity was NOT
arbitrary. A positive ground offers better protection against
corrosion:
<https://en.wikipedia.org/wiki/Tip_and_ring#Polarity>
To provide cathodic protection against corrosion of line
wires, operating potential of telephone lines is typically
negative with respect to ground, and the tip side is
generally close to the ground potential. Thus, all power
supplies for telecommunication equipment are designated to
supply a negative voltage.

When the internet was being built, data communications went via
telephone company services and lived in telephone company owned
central offices. These offices were powered by -48VDC power. It made
sense for the new internet services, switches, muxs, termination
equipment, PoE, etc to be powered by the same -48VDC power.

Please note that red=positive and black=negative is an color
automotive standard. Color codes are VERY different in other
industries.

Also, 48VDC is considered "safe" and suitable for using "low voltage
insulation". Any higher voltage requires additional protection.
However, in the electric power industry less than 50V is consider
"extra low voltage" while anything under 1000V is considered "low
voltage". Sigh.



--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[jla...@highlandsniptechnology.com]

I had a British car once with positive ground.

I had to replace the battery and, instinctively, strapped the negative
lug to the chassis. When I connected the other cable and got a big
spark, I understood the situation in milliseconds. Too many
milliseconds!

I blew out all the diodes in the alternator, and replaced them with a
couple of big Motorola bridge rectifiers. Luckily, the radio was off
at the time.

I'm working with alternators again, FADEC power supplies. You short a
PM alternator to regulate the output.

I think positive ground has some sort of corrosion advantage.



--

John Larkin Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.
"Bunter", he said, "I give you a toast. The triumph of Instinct over Reason"

[Michael Nagel]

Am 25.01.20 um 20:57 schrieb Jeff Liebermann:

Amen.

A few additions:

The terminology is TNV-x (TNV-1 or TNV-2 or TNV-3).
Here is a nice tutorial:
https://www.ewh.ieee.org/r6/scv/pses/ieee_scv_pses_jun07.pdf

The IEC/EC/UL 60950-1 is past its DoW.
It has been replaced with the IEC 62368-1.
Many standards still refer to the 60950-1 and it will take at least
another decade until this has changed.

Michael

[DecadentLinux...@decadence.org]

Michael Nagel <m_nagel@muenchen [remove this] -mail.de> wrote in
news:r0i8pk$eq9$1...@news-1.m-online.net:

Great link... thanks.

[Grant Taylor]

On 1/25/20 12:28 PM, George Herold wrote:
> Right, Say you have a 48V battery.

Okay.

> You hook up the neg. terminal to ground, you've got +48V at the
> positive terminal.
> You hook up the pos. terminal to ground and it's -48V at the negative
> terminal.

This seems to assume that you hook the negative terminal of your meter
to ground and the positive terminal of your meter to the other battery
terminal.

So with a positive ground system, the meter's negative terminal is
hooked to the batteries positive terminal and the meter's positive
terminal is hooked to the batteries negative terminal.

This I think that "ground" / "common" is largely irreverent in this
scenario. The only way that I think it starts to make any difference is
if you don't measure at the batteries terminals and instead measure off
of a different circuit in the car reference to common.

[Steve Wilson]

jla...@highlandsniptechnology.com wrote:

> I think positive ground has some sort of corrosion advantage.

Not in cars. For telephone wires, it's a different story.

It's simnple high school chemistry. Electrolysis liberates metal ions at the
positive terminal and produces OH- at the negative terminal.

when copper is at the positive terminal, copper ions are released. This
corrodes the copper.

When copper is at the negative terminal, there is only OH- produced. There is
no corrosion.

Telephone companies can drive a large ground rod into the soil to take care
of the loss of ions at the positive terminal. This protects the positive
copper terminal from corrosion. Since there is no corrosion at the negative
terminal, the copper wires are protected and can remain buried forever.

[Grant Taylor]

On 1/25/20 12:33 PM, Rick C wrote:
> I'm at a loss to understand what you are confused about. Do you have
> any specific questions???

I have a -48 VDC power supply with an unlabeled terminal and a return
terminal.

Other sets of DC equipment & associated supplies (multiple small sets of
different supplies and equipment used for various things) use red and
black wire.

What is return? red or black

What voltage should be read when connecting the meter's positive / red
lead and negative / black lead to the red & black wires from the DC supply?

How should things be wired to a piece of equipment that has the ground
symbol on one terminal and the other terminal unlabeled?

My brain is having problems aggregating all of these and making
associations.

> How does any of this impact using the 48 volts to supply the equipment
> you list? In other words, why are you confused?

Which terminal of the DC source; unlabled and return, connects to the
ground terminal on the DC load equipment?

[Grant Taylor]

On 1/25/20 12:57 PM, Jeff Liebermann wrote:
> Please note that red=positive and black=negative is an color automotive
> standard. Color codes are VERY different in other industries.

All of the -48 VDC equipment that I've seen used have used red, black,
and maybe green for a safety ground.

I think that red is the "hot" wire with -48 VDC with reference to the
black "common" wire. But I'm not sure.

See my other message ~5 minutes ago for more details.

[Grant Taylor]

On 1/25/20 1:42 PM, Steve Wilson wrote:
> Telephone companies can drive a large ground rod into the soil to take
> care of the loss of ions at the positive terminal. This protects the
> positive copper terminal from corrosion. Since there is no corrosion
> at the negative terminal, the copper wires are protected and can
> remain buried forever.

Interesting. So the ground rod is for more than just safety. It's
actually used to control / prevent corrosion too.

[Dean Hoffman]

I guess pipeline companies bury old pipe out in fields then send
some current out to the buried pipe. That protects the actual pipeline
they want to use.

[George Herold]

Voltages are about differences. You have to set 'zero' somewhere...
or we can't really talk about it. Ground is a common point (NPI)
you can float everything above ground... but it gets dangerous to touch
above ~60V (depends on source impedance)
GH.
Are you an EE?

[George Herold]

Go to harbor freight (assuming you live in US) buy the cheap DMM
and measure it! Otherwise you have no idea how red and black are set.
GH

[mpm]

On Saturday, January 25, 2020 at 3:49:25 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 12:57 PM, Jeff Liebermann wrote:
> > Please note that red=positive and black=negative is an color automotive
> > standard. Color codes are VERY different in other industries.
>
> All of the -48 VDC equipment that I've seen used have used red, black,
> and maybe green for a safety ground.
>
> I think that red is the "hot" wire with -48 VDC with reference to the
> black "common" wire. But I'm not sure.
>

Here is the DC color code used by two very large US wireless carriers (i.e., cell phone providers) at their cell sites (and, signal sources like HetNet that act like "mini-cell sites"):

Coming off the batteries to the rectifier: (Input to the rectifier)
(The rectifier keeps the batteries charged.)
Black = Negative
Red = +48 VDC

Output of the rectifier feeding all the radio & other cell site equipment:
(Note: This is usually the input to a PDU, which is a fused Power Distribution Unit - a fancy name for a fused distribution block, panel-mount.)
And everything at many cell sites is 48 VDC, including the overhead lights, and sometimes even the air conditioning.

Black = Negative 48 VDC
There is a saying in the industry: "Black to the breaker."

Grey (or White) = Return (this is 0-VDC potential relative to Earth ground), and at the rectifier, is bonded to..

Green = Earth Ground (i.e., the main facility ground bus bar)
The equipment racks are also connected to ground using Green cable.

The cables used are typically TelcoFlex-III, 600 Volt. ($$ expensive cable)
I've seen anywhere from #10 AWG to #2 AWG, depending on how many cell site radios are installed.

[jla...@highlandsniptechnology.com]

One almost always connects a meter negative terminal to ground. That
way, you can see if the voltage you're measuring is positive or
ground.

[jla...@highlandsniptechnology.com]

Ignore ricky. He doesn't want to help, he wants to insult.

Most of what he says translates to "you are stupid."

[Rick C]

On Saturday, January 25, 2020 at 3:44:27 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 12:33 PM, Rick C wrote:
> > I'm at a loss to understand what you are confused about. Do you have
> > any specific questions???
>
> I have a -48 VDC power supply with an unlabeled terminal and a return
> terminal.

Unless there is a connection within the power supply to earth ground or some other reference point such as a ground for a control signal, the power supply is just a 48 volt power supply. One terminal is positive and the other negative.

When you say "return" terminal, what do you see that distinguishes the two terminals? Is one labeled "return"? Is that the positive terminal? If you plug it in and measure the terminals to earth ground, what do you get? If one approximately zero volts and the other positive or negative? You may need to put a 1 kohm resistor across the meter to prevent seeing stray voltage while you do this.

> Other sets of DC equipment & associated supplies (multiple small sets of
> different supplies and equipment used for various things) use red and
> black wire.
>
> What is return? red or black

In typical DC electronics, red is positive and black negative. I don't work with -48 volt circuits a lot, so I can't say that this applies for that.

> What voltage should be read when connecting the meter's positive / red
> lead and negative / black lead to the red & black wires from the DC supply?

What is the existing system using? I would go with that unless you want to rewire the whole thing.

> How should things be wired to a piece of equipment that has the ground
> symbol on one terminal and the other terminal unlabeled?

Is the equipment designed for -48 volts? If so connect accordingly. I guess you are asking about colors. I don't know convention other than in smaller gear where red is positive and black is negative.

> My brain is having problems aggregating all of these and making
> associations.

The main thing is to not think in terms of "reference" or "ground" but positive and negative. You won't blow up things if you keep polarity straight.

> > How does any of this impact using the 48 volts to supply the equipment
> > you list? In other words, why are you confused?
>
> Which terminal of the DC source; unlabled and return, connects to the
> ground terminal on the DC load equipment?

If the equipment is not presently connected (for you to measure and copy), I recommend you get a manual for the equipment and find out what polarity they are expecting. Getting that wrong can destroy the equipment.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

[Rick C]

On Saturday, January 25, 2020 at 5:31:54 PM UTC-5, jla...@highlandsniptechnology.com wrote:
> On Sat, 25 Jan 2020 13:44:29 -0700, Grant Taylor
> <gta...@tnetconsulting.net> wrote:
>
> >On 1/25/20 12:33 PM, Rick C wrote:
> >> I'm at a loss to understand what you are confused about. Do you have
> >> any specific questions???
> >
> >I have a -48 VDC power supply with an unlabeled terminal and a return
> >terminal.
> >
> >Other sets of DC equipment & associated supplies (multiple small sets of
> >different supplies and equipment used for various things) use red and
> >black wire.
> >
> >What is return? red or black
> >
> >What voltage should be read when connecting the meter's positive / red
> >lead and negative / black lead to the red & black wires from the DC supply?
> >
> >How should things be wired to a piece of equipment that has the ground
> >symbol on one terminal and the other terminal unlabeled?
> >
> >My brain is having problems aggregating all of these and making
> >associations.
> >
> >> How does any of this impact using the 48 volts to supply the equipment
> >> you list? In other words, why are you confused?
> >
> >Which terminal of the DC source; unlabled and return, connects to the
> >ground terminal on the DC load equipment?
>
> Ignore ricky. He doesn't want to help, he wants to insult.
>
> Most of what he says translates to "you are stupid."

Notice the troll likes to demean and doesn't actually help much himself.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

[Whoey Louie]

On Saturday, January 25, 2020 at 3:44:27 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 12:33 PM, Rick C wrote:
> > I'm at a loss to understand what you are confused about. Do you have
> > any specific questions???
>
> I have a -48 VDC power supply with an unlabeled terminal and a return
> terminal.

So then there is -48V between the unlabeled terminal and the return.
But you'd think they would label that unlabeled terminal -48V or supply.

>
> Other sets of DC equipment & associated supplies (multiple small sets of
> different supplies and equipment used for various things) use red and
> black wire.
>
> What is return? red or black

The red side would be positive, the black negative. Current flows from
the positive side of the source to negative. So the return would be the
black, but that terminology isn't frequently used.

>
> What voltage should be read when connecting the meter's positive / red
> lead and negative / black lead to the red & black wires from the DC supply?

Take a 12 V power supply. If you connect the red meter lead to the red
on the power supply, black to black you'd read +12V. If you connect red
to black, black to red, you'd read -12V.

>
> How should things be wired to a piece of equipment that has the ground
> symbol on one terminal and the other terminal unlabeled?

Carefully. It's a very bad idea to have things unlabeled. Better
RTFM.

>
> My brain is having problems aggregating all of these and making
> associations.
>
> > How does any of this impact using the 48 volts to supply the equipment
> > you list? In other words, why are you confused?
>
> Which terminal of the DC source; unlabled and return, connects to the
> ground terminal on the DC load equipment?
>

You have what you say is a -48V supply and it has one terminal marked
return, the other unlabeled. Let's say you have a 48V piece of eqpt
and it has a red wire and black wire coming out of it or a red terminal
and black terminal. Knowing only the above, the logical thing is that
the unmarked supply terminal goes to the black/neg and the return terminal
goes to the red/positive.

[Whoey Louie]

And the latter is his "positive ground" system. As someone else pointed
out, ground in this case just means a system reference point.
As an example, cars today have a negative ground system, the battery negative
is connected to the car metal chassis, which is used as part of the
return path for current. Some cars years ago, instead had a positive
ground system, with the battery positive connected to the chassis instead.
It's like driving on the wrong side of the road, some just had to be
different. :) Fortunately with grounding, I think the weirdos wised
up and AFAIK no cars have been built for decades that have positive
ground.

[Sylvia Else]

In any system of connected wires at different potentials, you can
arbitrarily label one of them "ground", and then measure the potentials
of the other wires relative to your ground. You will then get some that
are positive, and some that are negative.

For some systems, such as a car, it can make some sense to label
whatever is connected to the chassis as ground, but it is still pretty
much an arbitrary choice.

And of course, with a fixed system, one can connect one point to the
soil under one's feet, and call that point ground.

But it's a naming convention, and nothing more.

In the absence of clear documentation on the system you're examining,
the only practical option is to take a multimeter to it, and make
measurements.

Sylvia

[Michael Terrell]

On Saturday, January 25, 2020 at 2:21:25 PM UTC-5, Grant Taylor wrote:

A communications system that I worked on for the International Space Station ran on -48VDC.

[Johnny B Good]

I should imagine for much the same reasons used to standardise road
vehicle ground reference polarity and telephone exchange equipment
grounding to earth - to minimise galvanic corrosion in vital metallic
structures - the inside would be a humid environment - it has to be for
the sake of the astronaut's respiratory health, providing ample
opportunity for the water vapour to condense out onto cold spots within
the structure of the ISS.

Incidentally, regarding the question of colour coding the polarity of
telecoms DC supplies, the GPO (as it was when I joined that organisation
as an apprentice in late '67) which is now known as BT (British Telecom),
the -52v "hot" (aka "Battery") exchange equipment bus bars were insulated
with blue plastic insulation (PVC afaicr) and the grounded (actually
earthed) positive bus bars were all left bare.

The fact that only the 'live' bus bars were insulated and the choice of
blue rather than black, were sufficient reminder (if a reminder was ever
needed) that the 'dangerous' pole of the 52v DC supply was negative with
respect to anything (all the exposed metalwork including the ground
return bus bars) at earth potential.

This scheme neatly eliminated any possible confusion that could arise
over which was the 'live' if the convention of red for positive and black
for negative had been followed (red for danger and black for the safety
of a conductor at ground potential failing to apply in this case).

As to whether or not this colour coding scheme was followed outside of
the UK and its dependencies (and the 48vdc power standards that came in
with the later solid state comms equipment), I know not so I'll leave
that as a question for old timers who've worked in telephone exchanges
outside of the UK to answer. ;-)

--
Johnny B Good

[jla...@highlandsniptechnology.com]

On Sun, 26 Jan 2020 13:31:52 +1100, Sylvia Else <syl...@email.invalid>
wrote:

The universe is probably absolute ground, and also defines absolute
zero velocity.

[Wond]

On Sat, 25 Jan 2020 12:21:25 -0700, Grant Taylor wrote:

> Is anyone willing to explain Negative 48 Volts DC?
>
> I'm trying to learn about it because we're using it for a few things at
> work (servers and switch equipment) and I'd like to better understand
> what we're working with than simply going through the motions that
> someone else dictates. Read: I want to understand and not simply rely
> on wrote memory.
>
> I've learned that -48 VDC uses what is called "Positive Ground" and that
> what I'm used to is called "Negative Ground".
>
> I'm trying to correlate and understand the typical red and black wires
> with them being ground / return / common / hot / etc.
>
> I suspect that there is more to it than simply reversing the + and -
> lead from a battery or meter. But I can't wrap my head around it.
>
> Can ~> will someone offer any comments that might help me understand
> better?

In a DC system, red is positive, black is negative, by convention.
Terms such as hot, return and ground are simply descriptive, and usually
applied in distributed AC in North America, where black is hot.

[Rick C]

Yeah, if we could just find the middle of it. Well, the part we can see anyway. What if we are off in a corner of the universe expanding away from the center at greater than the speed of light?

So if the universe started as a singularity and expanded from there, how could any part of it speed away and become invisible by exceeding the speed of light?

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

[mpm]

On Sunday, January 26, 2020 at 2:10:41 AM UTC-5, Michael Terrell wrote:
> A communications system that I worked on for the International Space Station ran on -48VDC.

I don't know if it is still the case, but that last (and probably only) time I had to install a two-way radio into a backhoe or bulldozer - that was a "positive ground" system.

I remember it because there was a circuit on the microphone hang-up clip that would automatically un-squelch the receiver (it used ground). But in this case, we had to isolate the chassis of the two-way radio from "ground", as to avoid a short. I forget what we did as a workaround. I think the antenna was also one of those Motorola NMO-type mounts (also "grounded"), so we had to do something to that too.

Someone earlier mentioned that "positive ground" systems tend to slow down corrosion. I don't know if that's true with backhoes, but they do spend their lives outdoors in the elements? (But so do cars, mostly.)

[Grant Taylor]

On 1/25/20 2:34 PM, George Herold wrote:
> Voltages are about differences. You have to set 'zero' somewhere...
> or we can't really talk about it. Ground is a common point (NPI)
> you can float everything above ground... but it gets dangerous to touch
> above ~60V (depends on source impedance)
> GH.
> Are you an EE?

No. I'm a systems / network administrator by trade. I'm just trying to
understand (more than wrote memory) how some of the equipment I
administer works.

There are other, more skilled people between me and connecting equipment.

[Grant Taylor]

On 1/25/20 3:54 PM, Rick C wrote:
> Unless there is a connection within the power supply to earth ground
> or some other reference point such as a ground for a control signal,
> the power supply is just a 48 volt power supply. One terminal is
> positive and the other negative.

I naively agree with you. But the negative part of -48 VDC confuses me
on what the positive and negative lead is. :-/

> When you say "return" terminal, what do you see that distinguishes
> the two terminals? Is one labeled "return"?

Yes. One terminal is labeled "return" and the other terminal is unlabled.

> Is that the positive terminal? If you plug it in and measure the
> terminals to earth ground, what do you get? If one approximately
> zero volts and the other positive or negative?

I have not yet done this test.

> You may need to put a 1 kohm resistor across the meter to prevent
> seeing stray voltage while you do this.

Yep. I'm familiar with this.

> In typical DC electronics, red is positive and black negative.

This matches my experience.

> I don't work with -48 volt circuits a lot, so I can't say that this
> applies for that.

My limited experience with -48 VDC makes me think that it does not.
Hence my desire to get a better understanding of -48 VDC.

> What is the existing system using? I would go with that unless you
> want to rewire the whole thing.

Sadly, the few pieces of -48 VDC equipment that I have are all using
small AC to DC power supplies for each piece of -48 VDC equipment. Both
the supplies and the equipment are unique. There's nothing really
common to look at. Save for the red and black wires. But with nothing
else common to match against, it's tough to tell.

> Is the equipment designed for -48 volts?

Yes.

> If so connect accordingly. I guess you are asking about colors.

I'm asking multiple questions in the hopes of getting a general
understanding. I'd like to have more than simple wrote memory.

> I don't know convention other than in smaller gear where red is
> positive and black is negative.

That's where the bulk of my experience is too.

> The main thing is to not think in terms of "reference" or "ground"
> but positive and negative. You won't blow up things if you keep
> polarity straight.

If I put on blinders and look at just the positive / negative and what
each piece of equipment wants, I agree.

I'm trying to learn more about how the multiple pieces of equipment work
together as a system.

> If the equipment is not presently connected (for you to measure and
> copy), I recommend you get a manual for the equipment and find out
> what polarity they are expecting. Getting that wrong can destroy
> the equipment.

Yep. I know that the equipment is -48 VDC. I know that the supply
provides -48 VDC. I'm just not clear on which terminal needs to be
connected to what. Yes the manuals will be involved.

[Rick C]

On Sunday, January 26, 2020 at 1:36:16 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 3:54 PM, Rick C wrote:
> > Unless there is a connection within the power supply to earth ground
> > or some other reference point such as a ground for a control signal,
> > the power supply is just a 48 volt power supply. One terminal is
> > positive and the other negative.
>
> I naively agree with you. But the negative part of -48 VDC confuses me
> on what the positive and negative lead is. :-/

Unfortunately that question is confusing to me. lol One terminal is positive and the other negative. Unless there is an internal connection to ground (like the power line safety ground - which there shouldn't be) it doesn't make any real sense to call it a -48 volt supply.

That's the part I'm not getting. Does the power supply actually say it is a -48 volt supply or just 48 volts? Or is the -48 volts just what you see in references to the supply elsewhere?

Bottom line is there's nothing unexpected going on. If it is wired for a -48 volt supply it will have the positive terminal wired to ground and the other terminal will be -48 volts. I can't tell you anything about how the terminals are labeled and I would not assume anything unless the labels on the supply are a bit more clear.

> > When you say "return" terminal, what do you see that distinguishes
> > the two terminals? Is one labeled "return"?
>
> Yes. One terminal is labeled "return" and the other terminal is unlabled.
>
> > Is that the positive terminal? If you plug it in and measure the
> > terminals to earth ground, what do you get? If one approximately
> > zero volts and the other positive or negative?
>
> I have not yet done this test.

The supply could very well be intended for -48 volt use with a positive ground and so the label "return" means positive. Or it could also be a typical supply with a positive output and a negative return. Is there a label with model number, maker's name, other identification? Find that and look up a data sheet.

> > You may need to put a 1 kohm resistor across the meter to prevent
> > seeing stray voltage while you do this.
>
> Yep. I'm familiar with this.
>
> > In typical DC electronics, red is positive and black negative.
>
> This matches my experience.
>
> > I don't work with -48 volt circuits a lot, so I can't say that this
> > applies for that.
>
> My limited experience with -48 VDC makes me think that it does not.
> Hence my desire to get a better understanding of -48 VDC.

When you say a better "understanding" you mean of the color code conventions? Technically it's all just wires and polarity, not much to understand.

> > What is the existing system using? I would go with that unless you
> > want to rewire the whole thing.
>
> Sadly, the few pieces of -48 VDC equipment that I have are all using
> small AC to DC power supplies for each piece of -48 VDC equipment. Both
> the supplies and the equipment are unique. There's nothing really
> common to look at. Save for the red and black wires. But with nothing
> else common to match against, it's tough to tell.

That's what I'm asking, the wiring colors. Are they consistent?

> > Is the equipment designed for -48 volts?
>
> Yes.
>
> > If so connect accordingly. I guess you are asking about colors.
>
> I'm asking multiple questions in the hopes of getting a general
> understanding. I'd like to have more than simple wrote memory.

Yes, you keep saying that, but you don't really say what is not clear. Maybe rote memory is good enough for now and a light bulb will come on later. That has happened for me in many areas.

> > I don't know convention other than in smaller gear where red is
> > positive and black is negative.
>
> That's where the bulk of my experience is too.
>
> > The main thing is to not think in terms of "reference" or "ground"
> > but positive and negative. You won't blow up things if you keep
> > polarity straight.
>
> If I put on blinders and look at just the positive / negative and what
> each piece of equipment wants, I agree.

I don't know what you mean by "blinders". You seem to think there is some greater understanding, but in reality it's all just a matter of polarity and the conventions are just that, conventions.

> I'm trying to learn more about how the multiple pieces of equipment work
> together as a system.

Do you have a question?

> > If the equipment is not presently connected (for you to measure and
> > copy), I recommend you get a manual for the equipment and find out
> > what polarity they are expecting. Getting that wrong can destroy
> > the equipment.
>
> Yep. I know that the equipment is -48 VDC. I know that the supply
> provides -48 VDC. I'm just not clear on which terminal needs to be
> connected to what. Yes the manuals will be involved.

Positive to positive and negative to negative. It's literally that simple. Since the vendors of the equipment seem to be fuzzy on labeling terminals, at least on the power supply, you should measure everything.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

[Rick C]

On Sunday, January 26, 2020 at 1:36:16 PM UTC-5, Grant Taylor wrote:
> On 1/25/20 3:54 PM, Rick C wrote:
> > Unless there is a connection within the power supply to earth ground
> > or some other reference point such as a ground for a control signal,
> > the power supply is just a 48 volt power supply. One terminal is
> > positive and the other negative.
>
> I naively agree with you. But the negative part of -48 VDC confuses me
> on what the positive and negative lead is. :-/

This seems to be the question you are asking I guess.

If you are working with a -48 volt system, the ground will be positive and the power lead will be negative. If your power supply is intended for such a system the lead labeled "return" will be positive and the other output will be negative.

It would be helpful to see some photos of the terminals and the power supply label.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

[George Herold]

OK, that makes sense. Good on you for trying to figure it out.
probably you can get one of the tech guys to show you the voltage on a
DMM (volt meter). (and even compare to ground on the ac plug.)

George H.

[Jeff Liebermann]

On Sun, 26 Jan 2020 10:16:41 -0800 (PST), mpm <mpmi...@aol.com>
wrote:

>On Sunday, January 26, 2020 at 2:10:41 AM UTC-5, Michael Terrell wrote:
>> A communications system that I worked on for the International Space Station ran on -48VDC.

Hmmm... I guess the ISS doesn't need to worry about ground leakage.

>I don't know if it is still the case, but that last (and probably only) time
>I had to install a two-way radio into a backhoe or bulldozer - that was
>a "positive ground" system.

In 1971, after graduating college directly into a recession, the only
job I could find was working for the local 2-way radio shop. I spend
2 months installing Motorola Motrac radios in concrete trucks. I
think they were either Mack or Peterbilt but I'm not sure. Most had
positive ground system. There were also some 24 volt systems (2
batteries in series) but we were able to tap off one battery.

Somewhat later, I found myself servicing and later selling marine
radios. On larger metal hull vessels, both the positive and negative
lines are floating. Therefore, all our early marine radios had
floating grounds. Eventually, a separate 12V power system was
introduced for powering radios and such, which had a negative ground.
Eventually, we supplied positive ground 12V radios on special order,
where all the electronics was grounded to the chassis though multiple
capacitors.

>I remember it because there was a circuit on the microphone hang-up
>clip that would automatically un-squelch the receiver (it used ground).

Ummm... if that were Motorola, it would be called a "hangup switch".
It did have anything to do with the noise squelch but did turn off the
PL (Private Line) tone squelch decoder. Usually, the button on the
back of the microphone was connected to ground when the PL was enabled
through the "microphone hanger". However, for positive ground system,
there was an isolated leaf switch inside the "hangup switch" and the
button on the back of the microphone was not used.

>But in this case, we had to isolate the chassis of the two-way
>radio from "ground", as to avoid a short. I forget what we did
>as a workaround.

Sounds like a later model radio that didn't have a positive ground
feature or option. I've seen radios installed on wooden platforms to
provide the necessary insulation. A plastic case microphone, isolated
hangup switch, and capacitor coupling the antenna coax ground were
also common.

>I think the antenna was also one of those Motorola NMO-type mounts
>(also "grounded"), so we had to do something to that too.

I've seen what happens when someone forgets about NOT ground the
antenna shield. Things mostly work ok, until someone blows the fuse
in the negative power line. That makes the only path to battery
negative through the coax cable ground. It usually works ok, until
someone keys the transmitter. The coax shield becomes hot enough to
melt the outer jacket and possibly set fire to everything nearby.

>Someone earlier mentioned that "positive ground" systems tend
>to slow down corrosion. I don't know if that's true with backhoes,
>but they do spend their lives outdoors in the elements? (But
>so do cars, mostly.)

The corrosion aspect was important for telco plant, but less so for
automotive. For cars, the manufacturers wanted to save money. Why
waste money on copper "ground" wire when they can run the current
though the body of the car. At high currents, that was also good for
re-heating all the Unibody spot welds. Usually about 10% of these
welds would fail, which was not enough to ruin the integrity of the
chassis, but was sufficient to create enough squeaks and rattles to
drive the owner nuts. With such an arrangement, it really doesn't
matter whether the chassis is positive or negative polarity. Road
salt is sufficient to guarantee that the body rots out at about the
same time as the other major components fail. I don't know why
negative ground was selected, but there are a variety of theories.
Here's one that suggests it was because the original cloth insulation
would leak current when wet and cause corrosion:
<http://www.cruisersforum.com/forums/f14/negative-ground-vs-positive-ground-history-question-184600.html>

Incidentally, Motorola decided to run two really heavy cables directly
between the trunk mounted radio and the battery under the hood.
However, they got cheap and lazy with their front and dash mounted
radios by supplying fairly short power cables with the radios.
Installers were tempted to just ground the negative to the car chassis
and were then blessed with alternator whine, generator whine, and
vibrator hash on transmit.

Not wishing to repeat all the mistakes of past attempts to color code
the power wiring, the solar power standard committees decided that it
would be better to label these in English and use the colors in their
original manner (red=danger, green=working, yellow=warning,
black=all_else). So, it is now mandatory to attach stickers on
everything including the DC power cables:
<https://www.google.com/search?tbm=isch&q=solar+power+warning+labels>
However, the DC power labels do not mention polarity. Instead the are
yellow and say "Solar Circuit". Most (not all) of the panels I've
seen use red and black color coded wires. NEC 2014 wasn't bad for a
first attempt at labeling, but did require a rewrite in 2017 to make
the English intelligible.
<https://www.solarpowerworldonline.com/2016/03/new-nec-2017-brings-clarity-solar-pv-labeling/>
I expect the next generation of labels might add multiple languages,
hieroglyphics, and icons.


--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

[Grant Taylor]

On 1/26/20 1:37 PM, Rick C wrote:
> Unfortunately that question is confusing to me. lol

Sorry. I'll try restating.

I naively agree with you that one terminal is positive with respect to
the other terminal.

However, what this terminal is called, is confusing, particularly when
dealing with negative voltage.

Aside: Yes, this equipment is powered by /negative/ 48 VDC.
"Neg(ative) 48 (V(DC))" or some close variant (including the "negative
polarity) and "48" volts) is quite common phrasing as an alternate power
source in computer (particularly servers) and networking equipment.

Further Aside: I can't actually remember the last time I heard
reference to (positive) 48 VDC in computers & networking equipment.

I believe that if I hook the positive / red lead of a voltmeter to the
positive / red lead of a power supply, and the negative / black lead of
the volt meter to the negative / black lead of a power supply, I expect
the following voltages:

Standard bench top 12 VDC power supply: + 12 VDC
Negative 48 VDC telephone power supply: - 48 VDC

So what is called the positive or red lead actually is negative with
respect to what is called the negative or black lead.

I /think/ this is accurate. But I'm not sure. Nor do I actually
understand /why/ this is the way that it is. This thread is my attempt
to learn and understand. …how can a positive power wire have a
negative voltage on it?

> One terminal is positive and the other negative. Unless there is an
> internal connection to ground (like the power line safety ground -
> which there shouldn't be) it doesn't make any real sense to call it
> a -48 volt supply.

See above.

> That's the part I'm not getting.

I understand the confusion. Hence my trying to ask questions and learn.

> Does the power supply actually say it is a -48 volt supply

Simplistically, yes, the power supply does say that it's -48 VDC.

Less simplistically, the labeling may not say it in those words. It may
simply say the output is (nominally) -48 VDC. Some actually are labeled
as -48 VDC supplies.

> or just 48 volts? Or is the -48 volts just what you see in references
> to the supply elsewhere?

Nope. To the best of my knowledge, the "negative" is an important part
of the description. I don't think it's simply how it's connected in
relation to the 48 VDC.

> Bottom line is there's nothing unexpected going on. If it is wired
> for a -48 volt supply it will have the positive terminal wired to
> ground and the other terminal will be -48 volts. I can't tell you
> anything about how the terminals are labeled and I would not assume
> anything unless the labels on the supply are a bit more clear.
>

> The supply could very well be intended for -48 volt use with a positive
> ground and so the label "return" means positive. Or it could also
> be a typical supply with a positive output and a negative return.
> Is there a label with model number, maker's name, other identification?
> Find that and look up a data sheet.

That is my plan.

> When you say a better "understanding" you mean of the color code
> conventions? Technically it's all just wires and polarity, not much
> to understand.

No. It's more than just color code. As you say, colors are immaterial
and simply chosen based on convention.

I want to understand how the volt meter reading described above.

I want to understand how the following AC-to-DC power supplies work:

-⏚) AC-to-DC with a connection between neutral / ground and the - output.
+⏚) AC-to-DC with a connection between neutral / ground and the + output.

If I don't know which, +⏚ or -⏚, the AC-to-DC supply is and I bond the -
output to ⏚, I'm either going to be safe (-⏚) or quite unhappy (+⏚).

> That's what I'm asking, the wiring colors. Are they consistent?

The equipment all uses red and black wires. I don't know what the
potential is between each of them to ⏚ is, much less how they are labeled.

I will need to look when I get an opportunity to, probably on Tuesday.

> Yes, you keep saying that, but you don't really say what is not clear.

I hope this message has cleared some of this up.

> Maybe rote memory is good enough for now and a light bulb will come
> on later. That has happened for me in many areas.

Maybe. I dislike doing such.

> I don't know what you mean by "blinders".

I'm referring to the 48 VDC supply (negative omitted on purpose) coming
in on two wires to connect to a piece of equipment. I can ignore the
color of the wires, use a volt meter to identify which is + and - and
wire it to the equipment the way that it wants. But that ignores, or is
blind to, the actual colors of the wires and how it integrates to the
rest of the system.

> You seem to think there is some greater understanding, but in reality
> it's all just a matter of polarity and the conventions are just that,
> conventions.

I /think/ that it is more than just polarity. See the +⏚ and -⏚
examples above.

> Do you have a question?

I think I've asked, or at least alluded to, many in this thread. It's
difficult to word smith a question about a concept that is still unclear
to me. :-( I think this email has some better ""questions in the form
of "I want to understand". They aren't worded as questions per say.
But I hope they convey what I want to learn.

> Positive to positive and negative to negative. It's literally
> that simple. Since the vendors of the equipment seem to be fuzzy on
> labeling terminals, at least on the power supply, you should measure
> everything.


--

[Grant Taylor]

On 1/26/20 1:41 PM, Rick C wrote:
> This seems to be the question you are asking I guess.
>
> If you are working with a -48 volt system, the ground will be positive
> and the power lead will be negative.

Okay.

So what colors would you expect / assume the ground and power leads to
be? Black and red, respectively? Or red and black, respectively?

> If your power supply is intended for such a system the lead labeled
> "return" will be positive and the other output will be negative.

Okay.

Do you think it would be acceptable for the negative power lead to be
referred to as "hot"?

This does seem to answer part of what I'm wanting to know. I say "part"
because I think your answer likely does provide the wrote memory type of
information. And in a round about way makes it easier for me to point
to the other part that I'm trying to learn.

How did you come to saying that -48 the ground will be positive and the
power lead will be negative? What other information / knowledge did you
rely on to make that statement? That other information / knowledge is
the other part of what I'm wanting to learn and understand. The
intention being for me to learn the foundational knowledge to deduce
statements like you did without needing to rely on wrote memory. Does
that make sense?

> It would be helpful to see some photos of the terminals and the power
> supply label.

Agreed. I'm at home, and the equipment in question is at work. I doubt
that I'll be able to get any pictures before Tuesday.

[Rick C]

On Sunday, January 26, 2020 at 4:42:38 PM UTC-5, Grant Taylor wrote:
> On 1/26/20 1:37 PM, Rick C wrote:
> > Unfortunately that question is confusing to me. lol
>
> Sorry. I'll try restating.
>
> I naively agree with you that one terminal is positive with respect to
> the other terminal.
>
> However, what this terminal is called, is confusing, particularly when
> dealing with negative voltage.

That's why I would look at the documentation for the equipment/supply. If it is a -48 volt system it certainly would be ok to call the positive terminal "return" or "common". It would be ok to call the negative terminal "hot".

> Aside: Yes, this equipment is powered by /negative/ 48 VDC.
> "Neg(ative) 48 (V(DC))" or some close variant (including the "negative
> polarity) and "48" volts) is quite common phrasing as an alternate power
> source in computer (particularly servers) and networking equipment.
>
> Further Aside: I can't actually remember the last time I heard
> reference to (positive) 48 VDC in computers & networking equipment.

I have seen some systems use a negative ground with a 48 volt power source.

> I believe that if I hook the positive / red lead of a voltmeter to the
> positive / red lead of a power supply, and the negative / black lead of
> the volt meter to the negative / black lead of a power supply, I expect
> the following voltages:
>
> Standard bench top 12 VDC power supply: + 12 VDC
> Negative 48 VDC telephone power supply: - 48 VDC

Now you are talking color codes. I can't tell you what the color code is for a -48 volt system.

> So what is called the positive or red lead actually is negative with
> respect to what is called the negative or black lead.

"Called" vs. "looks" I can't say. I never talk about the "red" lead when dealing with power circuits. I use the other terms listed above.

> I /think/ this is accurate. But I'm not sure. Nor do I actually
> understand /why/ this is the way that it is. This thread is my attempt
> to learn and understand. …how can a positive power wire have a
> negative voltage on it?

Now you have me confused again. Who talked about a positive wire with a negative voltage??? Positive/negative are electric polarities and don't change when your definition of the common or ground changes.

> > One terminal is positive and the other negative. Unless there is an
> > internal connection to ground (like the power line safety ground -
> > which there shouldn't be) it doesn't make any real sense to call it
> > a -48 volt supply.
>
> See above.
>
> > That's the part I'm not getting.
>
> I understand the confusion. Hence my trying to ask questions and learn.
>
> > Does the power supply actually say it is a -48 volt supply
>
> Simplistically, yes, the power supply does say that it's -48 VDC.
>
> Less simplistically, the labeling may not say it in those words. It may
> simply say the output is (nominally) -48 VDC. Some actually are labeled
> as -48 VDC supplies.

Ok, if they say it's a -48 volt supply with a minus sign in front of the voltage, then it is safe to believe the hot wire will be the negative the return/common wire will be the positive.

> > or just 48 volts? Or is the -48 volts just what you see in references
> > to the supply elsewhere?
>
> Nope. To the best of my knowledge, the "negative" is an important part
> of the description. I don't think it's simply how it's connected in
> relation to the 48 VDC.

Ok, because I'm willing to bet the supply is not grounded, but it may be. If not grounded they are only calling it a -48 volt supply because that is how most people use it. There is nothing inherent that makes it minus vs. positive.

> > Bottom line is there's nothing unexpected going on. If it is wired
> > for a -48 volt supply it will have the positive terminal wired to
> > ground and the other terminal will be -48 volts. I can't tell you
> > anything about how the terminals are labeled and I would not assume
> > anything unless the labels on the supply are a bit more clear.
> >
> > The supply could very well be intended for -48 volt use with a positive
> > ground and so the label "return" means positive. Or it could also
> > be a typical supply with a positive output and a negative return.
> > Is there a label with model number, maker's name, other identification?
> > Find that and look up a data sheet.
>
> That is my plan.
>
> > When you say a better "understanding" you mean of the color code
> > conventions? Technically it's all just wires and polarity, not much
> > to understand.
>
> No. It's more than just color code. As you say, colors are immaterial
> and simply chosen based on convention.
>
> I want to understand how the volt meter reading described above.

The volt meter will always tell you the voltage between the two probes assuming the red will be positive and the black negative. If that is correct the meter will show a positive voltage. I the red lead is negative it will show a negative voltage.

> I want to understand how the following AC-to-DC power supplies work:
>
> -⏚) AC-to-DC with a connection between neutral / ground and the - output.

That will give you a positive voltage on the positive lead with respect to (wrt) ground.

> +⏚) AC-to-DC with a connection between neutral / ground and the + output.

That will give you a negative voltage on the negative lead wrt ground.

BTW, none of these supplies should have any connection to power line neutral. That is dangerous situation and can kill. Neutral is not ground (protective earth).

> If I don't know which, +⏚ or -⏚, the AC-to-DC supply is and I bond the -
> output to ⏚, I'm either going to be safe (-⏚) or quite unhappy (+⏚).

Why would you bond any voltage line to earth? Do your equipment systems use actual grounds anywhere? It's easy enough to measure the voltages and see if the power is connected to ground.

> > That's what I'm asking, the wiring colors. Are they consistent?
>
> The equipment all uses red and black wires. I don't know what the
> potential is between each of them to ⏚ is, much less how they are labeled.

I'd say a measurement is in order... with the resistor I mentioned.

> I will need to look when I get an opportunity to, probably on Tuesday.
>
> > Yes, you keep saying that, but you don't really say what is not clear.
>
> I hope this message has cleared some of this up.
>
> > Maybe rote memory is good enough for now and a light bulb will come
> > on later. That has happened for me in many areas.
>
> Maybe. I dislike doing such.
>
> > I don't know what you mean by "blinders".
>
> I'm referring to the 48 VDC supply (negative omitted on purpose) coming
> in on two wires to connect to a piece of equipment. I can ignore the
> color of the wires, use a volt meter to identify which is + and - and
> wire it to the equipment the way that it wants. But that ignores, or is
> blind to, the actual colors of the wires and how it integrates to the
> rest of the system.

That's the part I don't get. Once you measure the voltages on the wires and know what the terminals of your equipment need, what else is there to know about the "system"??? The only problem that could happen is if one of the power leads is grounded to the chassis and a piece of equipment connects power to the chassis, but they are different connections. That's why you read the documentation.

> > You seem to think there is some greater understanding, but in reality
> > it's all just a matter of polarity and the conventions are just that,
> > conventions.
>
> I /think/ that it is more than just polarity. See the +⏚ and -⏚
> examples above.

That is all polarity, no? I'm not getting it.

> > Do you have a question?
>
> I think I've asked, or at least alluded to, many in this thread. It's
> difficult to word smith a question about a concept that is still unclear
> to me. :-( I think this email has some better ""questions in the form
> of "I want to understand". They aren't worded as questions per say.
> But I hope they convey what I want to learn.
>
> > Positive to positive and negative to negative. It's literally
> > that simple. Since the vendors of the equipment seem to be fuzzy on
> > labeling terminals, at least on the power supply, you should measure
> > everything.

I hope that helps.

--

Rick C.

--- Get 1,000 miles of free Supercharging
--- Tesla referral code - https://ts.la/richard11209

[Rick C]

On Sunday, January 26, 2020 at 4:50:41 PM UTC-5, Grant Taylor wrote:
> On 1/26/20 1:41 PM, Rick C wrote:
> > This seems to be the question you are asking I guess.
> >
> > If you are working with a -48 volt system, the ground will be positive
> > and the power lead will be negative.
>
> Okay.
>
> So what colors would you expect / assume the ground and power leads to
> be? Black and red, respectively? Or red and black, respectively?

I don't assume something I don't know about. You'll have to measure.

> > If your power supply is intended for such a system the lead labeled
> > "return" will be positive and the other output will be negative.
>
> Okay.
>
> Do you think it would be acceptable for the negative power lead to be
> referred to as "hot"?

Hot or power. Ground/common is typically used for the "reference" of the power. So the other lead will be positive in this system and so, hot.

> This does seem to answer part of what I'm wanting to know. I say "part"
> because I think your answer likely does provide the wrote memory type of
> information. And in a round about way makes it easier for me to point
> to the other part that I'm trying to learn.
>
> How did you come to saying that -48 the ground will be positive and the
> power lead will be negative? What other information / knowledge did you
> rely on to make that statement?

Just that the definition of -48 volt power is that the negative is the power or hot lead and the positive is common.

I really shouldn't use "ground" for the common lead since ground is often used for "protective earth" which is a different concept. They may be connected, but are not the same thing, just as neutral and protective earth are connected (if all is well) but not the same thing.

If I mean protective earth I will say protective earth, otherwise ground will mean common.

> That other information / knowledge is
> the other part of what I'm wanting to learn and understand. The
> intention being for me to learn the foundational knowledge to deduce
> statements like you did without needing to rely on wrote memory. Does
> that make sense?

Not really. I think you are making this a bit too complicated than it is. I'm not complaining, just stating an observation.

> > It would be helpful to see some photos of the terminals and the power
> > supply label.
>
> Agreed. I'm at home, and the equipment in question is at work. I doubt
> that I'll be able to get any pictures before Tuesday.

I expect that by the time you get to the equipment this will all be much more clear to you.

--

Rick C.

--+ Get 1,000 miles of free Supercharging
--+ Tesla referral code - https://ts.la/richard11209

[mpm]

On Sunday, January 26, 2020 at 4:42:38 PM UTC-5, Grant Taylor wrote:

Grant, let me just offer this as consolation:

A few months back, we got a job to wire-up a Verizon rack.
The rectifier was an Emerson NetSure 502. (Pretty generic, in that industry).

Well.... You need a Ph.D. to understand the Installation Manual.
That manual covers so many different options and configurations it will make your head spin. The manuals (plural)are at least 3-inches thick, loaded with schematics and wiring diagrams to cover any situation and options packages known to mankind.

We sat there for about an hour with the manuals just trying to figure out where to connect the two leads from the battery. (A "-48 VDC" system.)

Getting nowhere - we finally called Emerson Tech Support.
I was mortified - how embarrassing to have to call in for this kind of stuff?!
You may as well wear a hat on your head that reads "I eat paint chips."

AN HOUR LATER - the rep was FINALLY able to tell us where to hook up!
Because even though Verizon probably buys these rectifiers by the 1000's, it's some special bus arrangement requiring the aforementioned Ph.D. to decipher the fucking manual.

Great product. Horrible manuals!
Unless all you do in life is focus on authoring manuals like that, and then of course, it's terrific.

But who has the time for that?

I guess I'm saying, don't feel bad about being confused.
Even the big guys fuck it up.

[whit3rd]

On Sunday, January 26, 2020 at 10:23:27 AM UTC-8, Grant Taylor wrote:
> On 1/25/20 2:34 PM, George Herold wrote:
> > Voltages are about differences. You have to set 'zero' somewhere...
> > or we can't really talk about it. Ground is a common point (NPI)
> > you can float everything above ground... but it gets dangerous to touch
> > above ~60V (depends on source impedance)
> > GH.
> > Are you an EE?
>
> No. I'm a systems / network administrator by trade. I'm just trying to
> understand (more than wrote memory) how some of the equipment I
> administer works.

For digital and analog signals, the 'ground' concept relates to signal return
currents, and completion of the electrical circuit. For digital outputs,
the logic 'zero' refers to voltages at/near ground
(negative ground for 5V or 3.3V logic), and 'one' to voltages far from ground. The
5V logic and 3.3V logic can share a ground connection, and interconnect,
thus that negative ground is the common connection (so 'common' often means 'ground').

For analog outputs (such as gigabit Ethernet levels) a good solution is to have
differential driven wires, with NO ground dependence, so that a voltage drop
in ground wires due to power fluctuations does not interfere with the signal
definition. For long wires, that is important.

Alternately, a metal chassis that has to be bonded (for safety) so as not to be
electrically active and cause a shock, has to be 'ground', and will connect
at various points to (for instance) the shielding on a video cable. Some signal
improvement results from such safety ground being either unconnected, or
simply (in only ONE PLACE) connected to the signal ground/analog ground/digital ground.

But, positive and negative power supply voltages are just... voltages that deliver power,
and don't have shielding requirements, nor (in general) do they have well-defined
immunity to noise and interference. That's why some logic (traditional ECL) uses
negative 5.2V, the noise on a power rail would contaminate the signal if that signal
were examined as a difference-from-positive-power-terminal, but not if that
signal was difference-from-negative-power-terminal.

Being confused is OK, but do NOT assume 'ground' is always the negative terminal of
a power supply, that is NOT OK.

[Rick C]

On Sunday, January 26, 2020 at 7:43:42 PM UTC-5, whit3rd wrote:
> On Sunday, January 26, 2020 at 10:23:27 AM UTC-8, Grant Taylor wrote:
> > On 1/25/20 2:34 PM, George Herold wrote:
> > > Voltages are about differences. You have to set 'zero' somewhere...
> > > or we can't really talk about it. Ground is a common point (NPI)
> > > you can float everything above ground... but it gets dangerous to touch
> > > above ~60V (depends on source impedance)
> > > GH.
> > > Are you an EE?
> >
> > No. I'm a systems / network administrator by trade. I'm just trying to
> > understand (more than wrote memory) how some of the equipment I
> > administer works.
>
> For digital and analog signals, the 'ground' concept relates to signal return
> currents, and completion of the electrical circuit. For digital outputs,
> the logic 'zero' refers to voltages at/near ground
> (negative ground for 5V or 3.3V logic), and 'one' to voltages far from ground. The
> 5V logic and 3.3V logic can share a ground connection, and interconnect,
> thus that negative ground is the common connection (so 'common' often means 'ground').

You seem to be saying there is a difference in the concept of ground for analog and digital circuits. Digital circuits are still analog electrically. They just have a much higher noise tolerance. But noise is still a significant issue and should not be ignored.

> For analog outputs (such as gigabit Ethernet levels) a good solution is to have
> differential driven wires, with NO ground dependence, so that a voltage drop
> in ground wires due to power fluctuations does not interfere with the signal
> definition. For long wires, that is important.

Exactly the same as digital. Differential pairs are commonly used to convey signals between boards or boxes.

> Alternately, a metal chassis that has to be bonded (for safety) so as not to be
> electrically active and cause a shock, has to be 'ground', and will connect
> at various points to (for instance) the shielding on a video cable. Some signal
> improvement results from such safety ground being either unconnected, or
> simply (in only ONE PLACE) connected to the signal ground/analog ground/digital ground.

Don't confuse the concepts of protective earth and signal ground. They are not always connected directly. When passing signals between boxes, even in the same rack, the "commonality" or protective ground is at question. Directly connecting grounds can cause large currents to flow in the ground conductor creating voltages that interfere with the signal.

Most of this has little or nothing to do with getting the polarity right on negative voltage power supplies. No need to overload the guy.

--

Rick C.

-+- Get 1,000 miles of free Supercharging
-+- Tesla referral code - https://ts.la/richard11209

[gray_wolf]

Years ago the Seeburg jukebox used a ferrite core memory to keep track of the
selections of records to be played. It replaced a lot of electro-mechanical
crap. It was all tube circuitry and the sense lead was was connected to a pulse
pulse amplifier in it's own little plugin metal box with a 12AX7, IIRC, and a
small ferrite looking pulse transformer contained therein. The module plugged
into the main control chassis. It's the only +V grounded circuit I've ever seen
except for some PNP germanium audio amplifiers and PNP computer stuff. I never
found the reason for this. I suspect it was done to increase the noise immunity.
I will say that the -V wire had quite a layer of dust attached to it. The
later NPN solid state versions used a -V ground with the sense lead went to the
base of a SCS, silicon controlled switch. Once it fired it stayed on until the
current flow was interrupted. Other than convention, I never cared which end of
the power supply was connected to ground. I never touch bare terminals to check
their potential to ground. I don't care what color they are.

[gray_wolf]

I think you have a poor understanding of basic current flow theory and likely
very little practical experience. This may be a good place to start. So your job
is connecting equipment to other equipment and you have no idea how to do this?

[Whoey Louie]

On Sunday, January 26, 2020 at 3:37:40 PM UTC-5, Rick C wrote:
> On Sunday, January 26, 2020 at 1:36:16 PM UTC-5, Grant Taylor wrote:
> > On 1/25/20 3:54 PM, Rick C wrote:
> > > Unless there is a connection within the power supply to earth ground
> > > or some other reference point such as a ground for a control signal,
> > > the power supply is just a 48 volt power supply. One terminal is
> > > positive and the other negative.
> >
> > I naively agree with you. But the negative part of -48 VDC confuses me
> > on what the positive and negative lead is. :-/
>
> Unfortunately that question is confusing to me. lol One terminal is positive and the other negative. Unless there is an internal connection to ground (like the power line safety ground - which there shouldn't be) it doesn't make any real sense to call it a -48 volt supply.

Sure it does. It's intended for use in a SYSTEM that uses -48V as
the power source.

>
> That's the part I'm not getting. Does the power supply actually say it is a -48 volt supply or just 48 volts? Or is the -48 volts just what you see in references to the supply elsewhere?

He clearly stated that one terminal is marked -48V, the other return.

[Whoey Louie]

On Sunday, January 26, 2020 at 4:42:38 PM UTC-5, Grant Taylor wrote:
> On 1/26/20 1:37 PM, Rick C wrote:
> > Unfortunately that question is confusing to me. lol
>
> Sorry. I'll try restating.
>
> I naively agree with you that one terminal is positive with respect to
> the other terminal.
>
> However, what this terminal is called, is confusing, particularly when
> dealing with negative voltage.

Why is it confusing? One terminal is the negative polarity, the other
the positive. On your supply, one terminal is marked -48V, the other
return. I would also make the -48V black, the return one red. but
even with just -48V on one and return on the other, it's clear which
is negative, which is positive. If you had a 9V battery and one terminal
was marked -9V, or 'neg", would you be confused about the polarity?

>
> Aside: Yes, this equipment is powered by /negative/ 48 VDC.
> "Neg(ative) 48 (V(DC))" or some close variant (including the "negative
> polarity) and "48" volts) is quite common phrasing as an alternate power
> source in computer (particularly servers) and networking equipment.
>
> Further Aside: I can't actually remember the last time I heard
> reference to (positive) 48 VDC in computers & networking equipment.
>
> I believe that if I hook the positive / red lead of a voltmeter to the
> positive / red lead of a power supply, and the negative / black lead of
> the volt meter to the negative / black lead of a power supply, I expect
> the following voltages:
>
> Standard bench top 12 VDC power supply: + 12 VDC
> Negative 48 VDC telephone power supply: - 48 VDC

Woah there Pilgrim! Are you saying on that -48V supply has a
RED terminal or wire for the -48V and BLACK for return? Now that I would
agree would be confusing. I would expect black to be on the -48V,
red on the return.

>
> So what is called the positive or red lead actually is negative with
> respect to what is called the negative or black lead.

It's either one polarity or the other, positive is never called negative.
What is called the "hot", the "source" or the "return" could be either
depending on the system polarity.

>
> I /think/ this is accurate. But I'm not sure. Nor do I actually
> understand /why/ this is the way that it is. This thread is my attempt
> to learn and understand. …how can a positive power wire have a
> negative voltage on it?

With one voltage, two wires like you have, it can't.

>
> > One terminal is positive and the other negative. Unless there is an
> > internal connection to ground (like the power line safety ground -
> > which there shouldn't be) it doesn't make any real sense to call it
> > a -48 volt supply.
>
> See above.
>
> > That's the part I'm not getting.
>
> I understand the confusion. Hence my trying to ask questions and learn.

But it does make sense. That power supply is designed to be used in a
positive ground system. So the supply terminal is labeled -48V.

So what color is the -48V terminal? Is there a color? I would expect it
to be either black or no color identification and the return to be either
red or no color.

>
> I want to understand how the volt meter reading described above.
>
> I want to understand how the following AC-to-DC power supplies work:
>
> -⏚) AC-to-DC with a connection between neutral / ground and the - output.
> +⏚) AC-to-DC with a connection between neutral / ground and the + output.

Why are you now adding neutral to this? Neutral is on the AC side.

[Whoey Louie]

On Sunday, January 26, 2020 at 4:50:41 PM UTC-5, Grant Taylor wrote:
> On 1/26/20 1:41 PM, Rick C wrote:
> > This seems to be the question you are asking I guess.
> >
> > If you are working with a -48 volt system, the ground will be positive
> > and the power lead will be negative.
>
> Okay.
>
> So what colors would you expect / assume the ground and power leads to
> be? Black and red, respectively? Or red and black, respectively?
>
> > If your power supply is intended for such a system the lead labeled
> > "return" will be positive and the other output will be negative.
>
> Okay.
>
> Do you think it would be acceptable for the negative power lead to be
> referred to as "hot"?

Sure, if it's a positive ground system, that would be correct. The
negative side of the supply is viewed as the source, the hot.

Imagine you are designing a new car with a 12V battery. Since the car
is made of metal, instead of using two wires to every light bulb, fan,
solenoid, you can use one "hot" wire to each and ground the other side
of the load to the metal chassis, using that as the return path to the
battery. So, one side of the battery gets connected to "ground"/chassis.
If it's the negative, like in all cars today, then it's a negative
ground system. Measuring between the hot side anywhere in the system
to ground you'd have +12V. Put the battery in the other way and you'd
have a positive ground system and you'd measure -12V.

>
> This does seem to answer part of what I'm wanting to know. I say "part"
> because I think your answer likely does provide the wrote memory type of
> information. And in a round about way makes it easier for me to point
> to the other part that I'm trying to learn.
>
> How did you come to saying that -48 the ground will be positive and the
> power lead will be negative? What other information / knowledge did you
> rely on to make that statement?

Did he say that? I hope not.


With your -48V supply, the -48V terminal would be called the "hot"
the "supply", but not the positive.

[Rick C]

As usual, you are wrong again, always wrong.

--

Rick C.

-++ Get 1,000 miles of free Supercharging
-++ Tesla referral code - https://ts.la/richard11209

[Rick C]

Please don't confuse the guy by not reading what he writes.

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

[Grant Taylor]

On 1/26/20 3:28 PM, Rick C wrote:
> That's why I would look at the documentation for the equipment/supply.

That is the plan. I've not had the opportunity to do so yet.

> If it is a -48 volt system it certainly would be ok to call the
> positive terminal "return" or "common". It would be ok to call the
> negative terminal "hot".

Okay.

> I have seen some systems use a negative ground with a 48 volt power
> source.

Fair enough. I've not had the exposure to (positive) 48 volt power.

> Now you are talking color codes. I can't tell you what the color
> code is for a -48 volt system.

I wasn't meaning to focus on the color code. Allow me to modify my
statement slightly by removing the colors from it.

I believe that if I hook the positive lead of a voltmeter to the
positive lead of a power supply, and the negative lead of the volt meter
to the negative lead of a power supply, I expect the following voltages:

Standard bench top 12 VDC power supply: + 12 VDC
Negative 48 VDC telephone power supply: - 48 VDC

> "Called" vs. "looks" I can't say. I never talk about the "red" lead
> when dealing with power circuits. I use the other terms listed above.

Okay.

> Now you have me confused again. Who talked about a positive wire with
> a negative voltage??? Positive/negative are electric polarities and
> don't change when your definition of the common or ground changes.

I believe it was a permutation of "hot" -> "red" -> "positive" in a
system that has negative voltage.

> Ok, if they say it's a -48 volt supply with a minus sign in front
> of the voltage, then it is safe to believe the hot wire will be the
> negative the return/common wire will be the positive.

Okay.

> Ok, because I'm willing to bet the supply is not grounded, but it
> may be. If not grounded they are only calling it a -48 volt supply
> because that is how most people use it. There is nothing inherent
> that makes it minus vs. positive.

I had a few minutes to look at the -48 VDC power supply today.

· The negative terminal was connected to the red wires.
· The positive terminal was connected to the black wires.
· The positive terminal was connected to the chassis.
· The chassis will make electrical contact with a rack that is
connected to earth ground.

> The volt meter will always tell you the voltage between the two
> probes assuming the red will be positive and the black negative.

The implication of polarity with volt meter leads doesn't help this
thread. But I generally agree with your statement.

> If that is correct the meter will show a positive voltage. I the
> red lead is negative it will show a negative voltage.

I believe the red lead does show a negative voltage.

> That will give you a positive voltage on the positive lead with
> respect to (wrt) ground.

I still need to measure, but I believe the positive lead has 0 volts to
ground.

> That will give you a negative voltage on the negative lead wrt ground.

Agreed.

> BTW, none of these supplies should have any connection to power line
> neutral. That is dangerous situation and can kill. Neutral is not
> ground (protective earth).

I agree that ground and neutral (in typical 120/240 VAC 1ɸ wiring) are
separate conductors and should not be used interchangeably. However,
ground and neutral are bonded together in the main electrical panel.
(At least every main panel that I've ever looked in. Sub-panels are
decidedly different with ground and neutral isolated from each other.)
So, there is a conductive path between ground and neutral.

> Why would you bond any voltage line to earth? Do your equipment
> systems use actual grounds anywhere? It's easy enough to measure
> the voltages and see if the power is connected to ground.

Ground is quite prevalent in networking equipment and servers. Some
vendors refuse to honor warranty if the equipment is not properly
grounded. Static is a (big) concern. So ground is used to dissipate
static before it builds up and causes problems.

> I'd say a measurement is in order... with the resistor I mentioned.

After looking at the -48 VDC power supply earlier today, I am quite
convinced that the positive terminal has electrical conductivity with
the building's earth ground. (Positive terminal strapped to chassis
which is bare metal connecting to the rack it mounts in (also bare
metal) which is earth grounded.)

> That's the part I don't get. Once you measure the voltages on the
> wires and know what the terminals of your equipment need, what else
> is there to know about the "system"??? The only problem that could
> happen is if one of the power leads is grounded to the chassis and
> a piece of equipment connects power to the chassis, but they are
> different connections. That's why you read the documentation.
>

> That is all polarity, no? I'm not getting it.
>

> I hope that helps.


--

[Grant Taylor]

On 1/26/20 4:02 PM, mpm wrote:
> Grant, let me just offer this as consolation:

…

> I guess I'm saying, don't feel bad about being confused.

~chuckle~

Thank you. I needed that. It's been a rough day.

> Even the big guys fuck it up.

Yep.

[Grant Taylor]

On 1/26/20 8:22 PM, gray_wolf wrote:
> I think you have a poor understanding of basic current flow theory and
> likely very little practical experience.

I /thought/ I had an acceptable understanding, particularly for a server
/ network administrator.

> This may be a good place to start.

> So your job is connecting equipment to other equipment and you have
> no idea how to do this?

That is a bit ambiguous.

My job is working with server and network equipment, including racking /
stacking / cabling (data and power). AC power is quite simple and to be
honest, hard to mess up. DC power is much more rare and requires being
more careful. Hence this thread.

Copper data connections can be tricky, particularly if equipment is
powered from different legs / phases and something about the power is
not correct. That's a great way to burn out ports. Sneak current's are
a bitch. Ground loops can be a problem if you're not careful. Optical
cables are safer to work with.

So, "connecting" is a bit ambiguous and can involve a number of
different things.

[Grant Taylor]

On 1/27/20 9:46 AM, Whoey Louie wrote:
> Why is it confusing? One terminal is the negative polarity, the other
> the positive. On your supply, one terminal is marked -48V, the other
> return. I would also make the -48V black, the return one red.

Having looked at the equipment earlier today, you'd be wrong.

Negative had the red wires.
Positive / ground had the black wires.

The confusion is understanding why things are wired the way that they are.

> but even with just -48V on one and return on the other, it's clear
> which is negative, which is positive. If you had a 9V battery and
> one terminal was marked -9V, or 'neg", would you be confused about
> the polarity?

In a negative ground system, no, I would not be confused.

In a positive ground system, I apparently am.

> Woah there Pilgrim! Are you saying on that -48V supply has a
> RED terminal or wire for the -48V and BLACK for return?

Yes!!!

That is EXACTLY what I'm saying. (See above.)

> Now that I would agree would be confusing.

Hence this thread.

> I would expect black to be on the -48V, red on the return.

Nope.

I don't know what I would have expected / guessed this time last week.
I'm loath to guess, lest I confuse myself more this week.

> It's either one polarity or the other, positive is never called negative.
> What is called the "hot", the "source" or the "return" could be either
> depending on the system polarity.

I'm slowly coming to the conclusion that I have naively assumed that red
≈ positive. Which is obviously wrong for positive ground systems.

I think I need to retrain myself that red = hot and that what is hot is
dependent on the type of system it is; negative ground or positive ground.

> With one voltage, two wires like you have, it can't.

I think that I need to reword my statement to be "a hot wire has a
negative voltage … in a positive ground system".

> But it does make sense. That power supply is designed to be used in a
> positive ground system. So the supply terminal is labeled -48V.

I checked, and one terminal is labeled "negative" and the other terminal
is labeled "positive".

> So what color is the -48V terminal? Is there a color? I would expect it
> to be either black or no color identification and the return to be either
> red or no color.

There is no color (save for polished / chrome steal).

The red wire was connected to negative. The black wire was connected to
positive.

I've not had the opportunity to measure the voltage yet. I'm planing on
doing that tomorrow.

> Why are you now adding neutral to this? Neutral is on the AC side.

I'm fairly certain that neutral and ground are bonded together somewhere
upstream. Thus I typed "neutral / ground" as "neutral or ground".
Because, from an electrical conductivity standpoint, they are at the
same potential and in some ways the same.

[Grant Taylor]

On 1/26/20 3:36 PM, Rick C wrote:
> I don't assume something I don't know about. You'll have to measure.

I'll try to make a point to do so tomorrow.

> Hot or power.

Okay.

Unless anyone objects, and provides an explanation of why they object,
I'm going to try to make a point to use the term "hot".

> Ground/common is typically used for the "reference" of the power.

I'm learning that.

Previously, I had assumed that ground / common also made reference to
the negative side. I'm having to unlearn that assumption as I go
through my Negative 48 Volt DC journey.

> So the other lead will be positive in this system and so, hot.

I want to agree, but I'm reticent because of the word "positive" in there.

I agree that hot will be positive in a negative ground system.

I'm learning that hot will be negative in a positive ground system.

> Just that the definition of -48 volt power is that the negative is
> the power or hot lead and the positive is common.

Thank you.

> I really shouldn't use "ground" for the common lead since ground
> is often used for "protective earth" which is a different concept.

Agreed.

I think chassis is another similar thing that can be used as a
reference, which may also be distinct from ground (protective earth).

> They may be connected, but are not the same thing, just as neutral and
> protective earth are connected (if all is well) but not the same thing.

Agreed.

> If I mean protective earth I will say protective earth, otherwise
> ground will mean common.

Okay.

> Not really. I think you are making this a bit too complicated than
> it is. I'm not complaining, just stating an observation.

Fair.

> I expect that by the time you get to the equipment this will all be
> much more clear to you.

It's starting to.

[Rick C]

On Monday, January 27, 2020 at 9:09:27 PM UTC-5, Grant Taylor wrote:
> On 1/26/20 3:28 PM, Rick C wrote:
> > That's why I would look at the documentation for the equipment/supply.
>
> That is the plan. I've not had the opportunity to do so yet.
>
> > If it is a -48 volt system it certainly would be ok to call the
> > positive terminal "return" or "common". It would be ok to call the
> > negative terminal "hot".
>
> Okay.
>
> > I have seen some systems use a negative ground with a 48 volt power
> > source.
>
> Fair enough. I've not had the exposure to (positive) 48 volt power.
>
> > Now you are talking color codes. I can't tell you what the color
> > code is for a -48 volt system.
>
> I wasn't meaning to focus on the color code. Allow me to modify my
> statement slightly by removing the colors from it.
>
> I believe that if I hook the positive lead of a voltmeter to the
> positive lead of a power supply, and the negative lead of the volt meter
> to the negative lead of a power supply, I expect the following voltages:
>
> Standard bench top 12 VDC power supply: + 12 VDC
> Negative 48 VDC telephone power supply: - 48 VDC

Positive and negative are electrical terms of physics. It has nothing to do with convention of colors or which polarity of common you use. Connect the positive meter probe to the positive power line and you will always measure a positive voltage no matter what.

> > "Called" vs. "looks" I can't say. I never talk about the "red" lead
> > when dealing with power circuits. I use the other terms listed above.
>
> Okay.
>
> > Now you have me confused again. Who talked about a positive wire with
> > a negative voltage??? Positive/negative are electric polarities and
> > don't change when your definition of the common or ground changes.
>
> I believe it was a permutation of "hot" -> "red" -> "positive" in a
> system that has negative voltage.

Let's forget color. If it is a -48 volt system the positive wire will be the common, but it will still be positive.

> > Ok, if they say it's a -48 volt supply with a minus sign in front
> > of the voltage, then it is safe to believe the hot wire will be the
> > negative the return/common wire will be the positive.
>
> Okay.
>
> > Ok, because I'm willing to bet the supply is not grounded, but it
> > may be. If not grounded they are only calling it a -48 volt supply
> > because that is how most people use it. There is nothing inherent
> > that makes it minus vs. positive.
>
> I had a few minutes to look at the -48 VDC power supply today.
>
> · The negative terminal was connected to the red wires.
> · The positive terminal was connected to the black wires.
> · The positive terminal was connected to the chassis.
> · The chassis will make electrical contact with a rack that is
> connected to earth ground.

Ok, so they are using the convention that red is "hot" and black is "common". They are also grounding their common to earth ground which is likely connected to a protective earth wire.

> > The volt meter will always tell you the voltage between the two
> > probes assuming the red will be positive and the black negative.
>
> The implication of polarity with volt meter leads doesn't help this
> thread. But I generally agree with your statement.
>
> > If that is correct the meter will show a positive voltage. I the
> > red lead is negative it will show a negative voltage.
>
> I believe the red lead does show a negative voltage.

I was talking about the voltmeter leads. But whatever.

> > That will give you a positive voltage on the positive lead with
> > respect to (wrt) ground.
>
> I still need to measure, but I believe the positive lead has 0 volts to
> ground.

You just said above the positive power lead is common and connected to a grounded chassis. You can't get any more zero than that. Of course you have to use common or ground as your reference (e.g. connect the black meter lead to common).

> > That will give you a negative voltage on the negative lead wrt ground.
>
> Agreed.
>
> > BTW, none of these supplies should have any connection to power line
> > neutral. That is dangerous situation and can kill. Neutral is not
> > ground (protective earth).
>
> I agree that ground and neutral (in typical 120/240 VAC 1ɸ wiring) are
> separate conductors and should not be used interchangeably. However,
> ground and neutral are bonded together in the main electrical panel.
> (At least every main panel that I've ever looked in. Sub-panels are
> decidedly different with ground and neutral isolated from each other.)
> So, there is a conductive path between ground and neutral.

And that is the hazard. If the neutral connection to the panel is lost, there is no return path for the power circuit and anything touching neutral will be hot. The bond between protective earth and neutral must be connected in a way that no failure can cause the protective earth to be hot.

> > Why would you bond any voltage line to earth? Do your equipment
> > systems use actual grounds anywhere? It's easy enough to measure
> > the voltages and see if the power is connected to ground.
>
> Ground is quite prevalent in networking equipment and servers. Some
> vendors refuse to honor warranty if the equipment is not properly
> grounded. Static is a (big) concern. So ground is used to dissipate
> static before it builds up and causes problems.

That would imply the equipment cabinet be grounded and the equipment connected to that. The power source can be floating and the equipment should not care. Do the equipment vendors define "properly grounded", that is, any specific instructions?

> > I'd say a measurement is in order... with the resistor I mentioned.
>
> After looking at the -48 VDC power supply earlier today, I am quite
> convinced that the positive terminal has electrical conductivity with
> the building's earth ground. (Positive terminal strapped to chassis
> which is bare metal connecting to the rack it mounts in (also bare
> metal) which is earth grounded.)

Is this strap at the power supply or the equipment being powered? Braided copper strap or just a regular wire? Just curious. As I've said, I've not worked with this sort of equipment.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

[Rick C]

On Monday, January 27, 2020 at 9:37:34 PM UTC-5, Grant Taylor wrote:
> On 1/26/20 3:36 PM, Rick C wrote:
> > I don't assume something I don't know about. You'll have to measure.
>
> I'll try to make a point to do so tomorrow.
>
> > Hot or power.
>
> Okay.
>
> Unless anyone objects, and provides an explanation of why they object,
> I'm going to try to make a point to use the term "hot".
>
> > Ground/common is typically used for the "reference" of the power.
>
> I'm learning that.
>
> Previously, I had assumed that ground / common also made reference to
> the negative side. I'm having to unlearn that assumption as I go
> through my Negative 48 Volt DC journey.

Yes, that is the only real difference.

> > So the other lead will be positive in this system and so, hot.
>
> I want to agree, but I'm reticent because of the word "positive" in there.

I'm talking about negative ground systems which I consider "typical".

> I agree that hot will be positive in a negative ground system.

Yes.

> I'm learning that hot will be negative in a positive ground system.

Yes.

> > Just that the definition of -48 volt power is that the negative is
> > the power or hot lead and the positive is common.
>
> Thank you.
>
> > I really shouldn't use "ground" for the common lead since ground
> > is often used for "protective earth" which is a different concept.
>
> Agreed.
>
> I think chassis is another similar thing that can be used as a
> reference, which may also be distinct from ground (protective earth).

No, any exposed metal is always connected to protective earth. That way no matter what happens with the power circuit (AC or DC) the exposed metal parts won't become "hot". Either a fuse will blow or the power source will blow up. lol

That may also be connected to the common power rail, but the point is it MUST be protective earth.

> > They may be connected, but are not the same thing, just as neutral and
> > protective earth are connected (if all is well) but not the same thing.
>
> Agreed.
>
> > If I mean protective earth I will say protective earth, otherwise
> > ground will mean common.
>
> Okay.
>
> > Not really. I think you are making this a bit too complicated than
> > it is. I'm not complaining, just stating an observation.
>
> Fair.
>
> > I expect that by the time you get to the equipment this will all be
> > much more clear to you.
>
> It's starting to.

Yeah, it's not hard, but takes a bit of work to get the mental connections correct.

--

Rick C.

++- Get 1,000 miles of free Supercharging
++- Tesla referral code - https://ts.la/richard11209

[Grant Taylor]

On 1/27/20 8:17 PM, Rick C wrote:
> Positive and negative are electrical terms of physics. It has nothing
> to do with convention of colors or which polarity of common you use.
> Connect the positive meter probe to the positive power line and you
> will always measure a positive voltage no matter what.

Presuming the negative meter probe is connected to negative power line,
and I agree.

The thing that I've learned is that there is no correlation between
"hot" / "common" / "return" / "ground" with positive or negative like I
have naively thought for the last 30 years.

> That would imply the equipment cabinet be grounded and the equipment
> connected to that. The power source can be floating and the equipment
> should not care. Do the equipment vendors define "properly grounded",
> that is, any specific instructions?

Yes. The better documentation calls out very specific directions on how
to bond ground to the equipment. They are quite specific about earth /
safety ground.

> Is this strap at the power supply or the equipment being powered?

It is part of part of the power supply.

> Braided copper strap or just a regular wire? Just curious. As I've
> said, I've not worked with this sort of equipment.

It is a piece of solid (what looks to be) steal that fits over the bolts
of the positive terminal where wires get bolted on top, thus sandwiching
the steal between the terminals and the restraining bolts. The other
end is bolted to the metal chassis.

[Grant Taylor]

On 1/27/20 8:39 PM, Rick C wrote:
> Yes, that is the only real difference.

*nod*

> I'm talking about negative ground systems which I consider "typical".

Fair enough.

I agree, negative ground has been about 99% of what I've seen and worked
around.

> No, any exposed metal is always connected to protective earth.
> That way no matter what happens with the power circuit (AC or DC)
> the exposed metal parts won't become "hot". Either a fuse will blow
> or the power source will blow up. lol

Sorry I mistyped, I was thinking where common and hot were floating
inside of and insulated from the chassis and the chassis itself is
grounded to earth. Thus chassis and and common can be at two different
potentials.

> That may also be connected to the common power rail, but the point
> is it MUST be protective earth.

*nod*

> Yeah, it's not hard, but takes a bit of work to get the mental
> connections correct.

Yep. Now that I've bifurcated ground / common from the negative
polarity, along with some better understanding of terms, I think I'm
starting to understand.

[Rick C]

On Monday, January 27, 2020 at 11:20:11 PM UTC-5, Grant Taylor wrote:
> On 1/27/20 8:17 PM, Rick C wrote:
> > Positive and negative are electrical terms of physics. It has nothing
> > to do with convention of colors or which polarity of common you use.
> > Connect the positive meter probe to the positive power line and you
> > will always measure a positive voltage no matter what.
>
> Presuming the negative meter probe is connected to negative power line,
> and I agree.
>
> The thing that I've learned is that there is no correlation between
> "hot" / "common" / "return" / "ground" with positive or negative like I
> have naively thought for the last 30 years.

That's because positive ground systems are the exception rather than the norm. Telephony related gear is an exception... when powered from 48 volts, but not always even then. I have seen gear that didn't have an internal connection to common and so could be used as positive ground or negative ground.

> > That would imply the equipment cabinet be grounded and the equipment
> > connected to that. The power source can be floating and the equipment
> > should not care. Do the equipment vendors define "properly grounded",
> > that is, any specific instructions?
>
> Yes. The better documentation calls out very specific directions on how
> to bond ground to the equipment. They are quite specific about earth /
> safety ground.
>
> > Is this strap at the power supply or the equipment being powered?
>
> It is part of part of the power supply.

That surprises me a bit. A AC/DC power supply output is typically isolated from the input power line, so common is whichever terminal you connect to... common. Having a connection internally to the AC protective earth limits the applications with no added advantage.

> > Braided copper strap or just a regular wire? Just curious. As I've
> > said, I've not worked with this sort of equipment.
>
> It is a piece of solid (what looks to be) steal that fits over the bolts
> of the positive terminal where wires get bolted on top, thus sandwiching
> the steal between the terminals and the restraining bolts. The other
> end is bolted to the metal chassis.

That sounds very external then. That makes sense. That's not really part of the power supply. They just provide the strap and you likely can use it on either output. But since the positive terminal is labeled "common", maybe not.

--

Rick C.

+++ Get 1,000 miles of free Supercharging
+++ Tesla referral code - https://ts.la/richard11209

[Michael Terrell]

On Sunday, January 26, 2020 at 4:30:12 PM UTC-5, Jeff Liebermann wrote:
> On Sun, 26 Jan 2020 10:16:41 -0800 (PST), mpm <mpmi...@aol.com>
> wrote:
>
> >On Sunday, January 26, 2020 at 2:10:41 AM UTC-5, Michael Terrell wrote:
> >> A communications system that I worked on for the International Space Station ran on -48VDC.
>
> Hmmm... I guess the ISS doesn't need to worry about ground leakage.
>
> >I don't know if it is still the case, but that last (and probably only) time
> >I had to install a two-way radio into a backhoe or bulldozer - that was
> >a "positive ground" system.
>
> In 1971, after graduating college directly into a recession, the only
> job I could find was working for the local 2-way radio shop. I spend
> 2 months installing Motorola Motrac radios in concrete trucks. I
> think they were either Mack or Peterbilt but I'm not sure. Most had
> positive ground system. There were also some 24 volt systems (2
> batteries in series) but we were able to tap off one battery.

There were plastic cases with Mobile CB radios mounded inside for Truckers, back in the '70s. They had a 6A or 25A full wave bridge on the DC input, and a mag mount antenna with a thicker than normal insulating pad on the mag mount, or a 1:! RF transformer to isolate the output for Mirror mount antennas. They were popular with Fleet truckers who never knew if the truck would have positive or negative ground. They were a pain in the ass on either grounding system, but truckers bought them.

[Michael Terrell]

On Sunday, January 26, 2020 at 4:30:12 PM UTC-5, Jeff Liebermann wrote:
>
> >On Sunday, January 26, 2020 at 2:10:41 AM UTC-5, Michael Terrell wrote:
> >
> >A communications system that I worked on for the International Space Station ran on -48VDC.
>
> Hmmm... I guess the ISS doesn't need to worry about ground leakage.

They used some COTS -48VDC items, so the entire station was designed to operate off the batteries and solar cells at that voltage.

The equipment that we supplied used a pair of Vicor 120/240 input supplies. One +5VDC and one +12/-12V dual output supply. It was a simple modification to replace them with a single, triple output,-48VDC input power supply. The biggest problem was that we only had one power supply at the factory that could power it, so it had to be moved from station to station through final test with the electronics.

[Michael Kellett]

On 25/01/2020 19:21, Grant Taylor wrote:
> Is anyone willing to explain Negative 48 Volts DC?
>
> I'm trying to learn about it because we're using it for a few things at
> work (servers and switch equipment) and I'd like to better understand
> what we're working with than simply going through the motions that
> someone else dictates.  Read:  I want to understand and not simply rely
> on wrote memory.
>
> I've learned that -48 VDC uses what is called "Positive Ground" and that
> what I'm used to is called "Negative Ground".
>
> I'm trying to correlate and understand the typical red and black wires
> with them being ground / return / common / hot / etc.
>
> I suspect that there is more to it than simply reversing the + and -
> lead from a battery or meter.  But I can't wrap my head around it.
>
> Can ~> will someone offer any comments that might help me understand
> better?
>
>
>

It's a very long time since I had anything to do with +ve earth British
Post Office stuff but as I recall we used to talk about battery and
earth. (Except the Irish guy I worked with, who used battery and ert.)
I have one or two examples of things I designed then (approx 1980, as
they (PO Telephones) were morphing into British Telecom) but no diagrams.
Here's a link to what looks like a fairly typical diagram:

http://finalselector.blogspot.com/2008/02/mystery-no-longer.html

You can see the use of earth and battery symbols.


This link is to a picture of a prototype relay tester (uses an Intel
8048 and designed to look as much like traditional relay based stuff as
possible). I don't have a schematic but you can see the names we used
and the on the front panle. The ETH wires are red.


https://www.dropbox.com/s/to75xfo3ujdjraz/LF1470.JPG?dl=0

MK

[DecadentLinux...@decadence.org]

Michael Kellett <m...@mkesc.co.uk> wrote in
news:e6SdnVob_YZ3m63D...@giganews.com:

>> Is anyone willing to explain Negative 48 Volts DC?
>>

Lead acid batteries used in system UPS's are 12V. Series 4 together
and get 48 Volts. Batteries are isolated sources, so either node can
be 'fashioned' as 'ground'. The power supplies used to charge such
battery back up systems had to make more than 48 Volts to make a
charge condition occur on the bank.

Whether they had individual battery watchdog circuits I do not
know, but having a bad cell in a 4 battery 48 Volt system causes less
of a droop than having a bad cell in a single battery 12 Volt system.
So the supply could be a bit down in voltage yet still do the needed
job.
Whereas a single battery or parallel bank may not be as happy with a
burned cell in play.

So my guess is that the voltage was chosen to match the current
storage cell technology of the times, and it simply stuck even though
electrical demands to perform the same jobs reduced as solid state
matured.

[Whoey Louie]

On Monday, January 27, 2020 at 9:09:27 PM UTC-5, Grant Taylor wrote:
> On 1/26/20 3:28 PM, Rick C wrote:
> > That's why I would look at the documentation for the equipment/supply.
>
> That is the plan. I've not had the opportunity to do so yet.
>
> > If it is a -48 volt system it certainly would be ok to call the
> > positive terminal "return" or "common". It would be ok to call the
> > negative terminal "hot".
>
> Okay.
>
> > I have seen some systems use a negative ground with a 48 volt power
> > source.
>
> Fair enough. I've not had the exposure to (positive) 48 volt power.
>
> > Now you are talking color codes. I can't tell you what the color
> > code is for a -48 volt system.
>
> I wasn't meaning to focus on the color code. Allow me to modify my
> statement slightly by removing the colors from it.
>
> I believe that if I hook the positive lead of a voltmeter to the
> positive lead of a power supply, and the negative lead of the volt meter
> to the negative lead of a power supply, I expect the following voltages:
>
> Standard bench top 12 VDC power supply: + 12 VDC
> Negative 48 VDC telephone power supply: - 48 VDC
>
> > "Called" vs. "looks" I can't say. I never talk about the "red" lead
> > when dealing with power circuits. I use the other terms listed above.
>
> Okay.

Not okay. If you hook the red positive lead of a meter to the positive and
the black negative lead to the neg of either power supply you will see +12V

>
> > Now you have me confused again. Who talked about a positive wire with
> > a negative voltage??? Positive/negative are electric polarities and
> > don't change when your definition of the common or ground changes.
>
> I believe it was a permutation of "hot" -> "red" -> "positive" in a
> system that has negative voltage.
>
> > Ok, if they say it's a -48 volt supply with a minus sign in front
> > of the voltage, then it is safe to believe the hot wire will be the
> > negative the return/common wire will be the positive.
>
> Okay.
>
> > Ok, because I'm willing to bet the supply is not grounded, but it
> > may be. If not grounded they are only calling it a -48 volt supply
> > because that is how most people use it. There is nothing inherent
> > that makes it minus vs. positive.
>
> I had a few minutes to look at the -48 VDC power supply today.
>
> · The negative terminal was connected to the red wires.
> · The positive terminal was connected to the black wires.
> · The positive terminal was connected to the chassis.
> · The chassis will make electrical contact with a rack that is
> connected to earth ground.

Weird and confusing to use red for the negative.

>
> > The volt meter will always tell you the voltage between the two
> > probes assuming the red will be positive and the black negative.
>
> The implication of polarity with volt meter leads doesn't help this
> thread. But I generally agree with your statement.
>
> > If that is correct the meter will show a positive voltage. I the
> > red lead is negative it will show a negative voltage.
>
> I believe the red lead does show a negative voltage.

Yes, because it's connected to -48V.

[Whoey Louie]

There is no such way. If the ground wire becomes disconnected at the panel,
or the wire is cut on it's way to the grounding electrode system and you
also have your disconnected neutral, the eqpt grounding system will become
energized through any loads.

[Whoey Louie]

On Tuesday, January 28, 2020 at 2:22:16 AM UTC-5, Rick C wrote:
> On Monday, January 27, 2020 at 11:20:11 PM UTC-5, Grant Taylor wrote:
> > On 1/27/20 8:17 PM, Rick C wrote:
> > > Positive and negative are electrical terms of physics. It has nothing
> > > to do with convention of colors or which polarity of common you use.
> > > Connect the positive meter probe to the positive power line and you
> > > will always measure a positive voltage no matter what.
> >
> > Presuming the negative meter probe is connected to negative power line,
> > and I agree.
> >
> > The thing that I've learned is that there is no correlation between
> > "hot" / "common" / "return" / "ground" with positive or negative like I
> > have naively thought for the last 30 years.
>
> That's because positive ground systems are the exception rather than the norm. Telephony related gear is an exception... when powered from 48 volts, but not always even then. I have seen gear that didn't have an internal connection to common and so could be used as positive ground or negative ground.
>
>
> > > That would imply the equipment cabinet be grounded and the equipment
> > > connected to that. The power source can be floating and the equipment
> > > should not care. Do the equipment vendors define "properly grounded",
> > > that is, any specific instructions?
> >
> > Yes. The better documentation calls out very specific directions on how
> > to bond ground to the equipment. They are quite specific about earth /
> > safety ground.
> >
> > > Is this strap at the power supply or the equipment being powered?
> >
> > It is part of part of the power supply.
>
> That surprises me a bit. A AC/DC power supply output is typically isolated from the input power line, so common is whichever terminal you connect to... common. Having a connection internally to the AC protective earth limits the applications with no added advantage.

Of course it has an advantage, lightning protection for one. Telco
offices, the DC side is connected to earth, for example. Or if an AC
conductor somewhere shorts to the DC side, it's likely to trip a
breaker, instead of energizing the DC side and going undetected.

[Whoey Louie]

On Monday, January 27, 2020 at 9:28:39 PM UTC-5, Grant Taylor wrote:
> On 1/27/20 9:46 AM, Whoey Louie wrote:
> > Why is it confusing? One terminal is the negative polarity, the other
> > the positive. On your supply, one terminal is marked -48V, the other
> > return. I would also make the -48V black, the return one red.
>
> Having looked at the equipment earlier today, you'd be wrong.
>
> Negative had the red wires.
> Positive / ground had the black wires.
>
> The confusion is understanding why things are wired the way that they are.

Yes, I see you said that in another post now too. And I agree, it is
confusing. I would not expect red to be the negative supply side and
black to be positive. That is confusing and asking for trouble.

>
> > but even with just -48V on one and return on the other, it's clear
> > which is negative, which is positive. If you had a 9V battery and
> > one terminal was marked -9V, or 'neg", would you be confused about
> > the polarity?
>
> In a negative ground system, no, I would not be confused.
>
> In a positive ground system, I apparently am.

Which end is designated the ground/return doesn't change the polarity
of the terminals at the power source.

>
> > Woah there Pilgrim! Are you saying on that -48V supply has a
> > RED terminal or wire for the -48V and BLACK for return?
>
> Yes!!!
>
> That is EXACTLY what I'm saying. (See above.)
>
> > Now that I would agree would be confusing.
>
> Hence this thread.

Yes, so then it's just a color choice thing. Which raises an interesting
question. In the small minority of cars that decades ago used a positive
ground, I wonder what color the supply wires were? Possible they were
red too. I've never seen one, IDK.

>
> > I would expect black to be on the -48V, red on the return.
>
> Nope.
>
> I don't know what I would have expected / guessed this time last week.
> I'm loath to guess, lest I confuse myself more this week.

Well, knowing that, just consider the red to be the supply side,
black to be the return. In the case of your -48V system, the red
then is the negative polarity.

>
> > It's either one polarity or the other, positive is never called negative.
> > What is called the "hot", the "source" or the "return" could be either
> > depending on the system polarity.
>
> I'm slowly coming to the conclusion that I have naively assumed that red
> ≈ positive. Which is obviously wrong for positive ground systems.

Red is positive in everything I've seen, but then all of that has been
negative ground, so I share your confusion. But some of it might become
obvious, even without looking at the power supply. If there are breakers
or fuses for example, they would be on the supply/hot side, so if those
wires were red and I knew it was a -48V system, I'd start wondering.

>
> I think I need to retrain myself that red = hot and that what is hot is
> dependent on the type of system it is; negative ground or positive ground.

Yes, at least for that particular system. The question is that what
all positive ground systems do?

>
> > With one voltage, two wires like you have, it can't.
>
> I think that I need to reword my statement to be "a hot wire has a
> negative voltage … in a positive ground system".

Yes, you've got it now.

>
> > But it does make sense. That power supply is designed to be used in a
> > positive ground system. So the supply terminal is labeled -48V.
>
> I checked, and one terminal is labeled "negative" and the other terminal
> is labeled "positive".
>
> > So what color is the -48V terminal? Is there a color? I would expect it
> > to be either black or no color identification and the return to be either
> > red or no color.
>
> There is no color (save for polished / chrome steal).
>
> The red wire was connected to negative. The black wire was connected to
> positive.
>
> I've not had the opportunity to measure the voltage yet. I'm planing on
> doing that tomorrow.
>
> > Why are you now adding neutral to this? Neutral is on the AC side.
>
> I'm fairly certain that neutral and ground are bonded together somewhere
> upstream. Thus I typed "neutral / ground" as "neutral or ground".
> Because, from an electrical conductivity standpoint, they are at the
> same potential and in some ways the same.
>

Yes, you have that correct too. Very normal for the return side of
eqpt to be connected to earth ground, for lightning, in case an AC
line side conductor somewhere gets shorted to the DC/low voltage side, etc.

[jrwal...@gmail.com]

On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote:

A couple of years ago I helped choose colours for the input connectors
of a networking product that had 12V (automotive range) and 48V
versions. The 12V choice was easy. We were using Anderson Powerpole
connectors, so we followed the amateur radio convention for these
connectors with red for positive and black for negative in a specific
configuration.
For 48V, I looked at every standard I could find and found a mass of
conflicting recommendations. An additional constraint was that we wanted
to use the "finger safe" version of the connectors and could only use
colours available from Anderson. Most customers would use positive
ground, but some had negative ground systems.
The final outcome was that the input was isolated with no connection
between either power terminal and chassis and the positive terminal
was red and the negative terminal was blue. This seemed to be in keeping
with the spirit of most of the standards and less likely to cause
confusion than any other combination.
Pictures at the bottom of the page:
https://www.firebrick.co.uk/fb2900/

John

[whit3rd]

On Tuesday, January 28, 2020 at 10:56:17 AM UTC-8, Whoey Louie wrote:

> ... I agree, it is

> confusing. I would not expect red to be the negative supply side and
> black to be positive. That is confusing and asking for trouble.

Alas, the innards of an automobile won't teach you anything bur red = positive.
There are LOTS of color conventions, many with legal enforcement, and
one must learn not to generalize.

In US house wiring, red would be AC high voltage. In a computer, red is +5V,
and yellow is +12V. In European AC cables, black is neutral, but in US
the white is neutral. Ground is sometimes black, sometimes green, and
green/yellow stripe is almost always ground.

I say 'almost always' because I've never seen (or used) it other than on ground wires, but
it's worth checking every time.

[Whoey Louie]

That's what I would have done too. I sure would not use red for negative
and black for positive. I was thinking about saying in the other reply
that if I decided to use black for the return in a positive ground system,
then I sure would not use red for the supply. I would use some other
color that would at least give someone looking at it reason to further
look into what's going on. When one sees just red and black in low
voltage DC system, one naturally assumes red is positive.

[Don Kuenz]

Whoey Louie <tra...@optonline.net> wrote:
> On Tuesday, January 28, 2020 at 2:33:22 PM UTC-5, jrwal...@gmail.com wrote:
>> On Tuesday, 28 January 2020 18:56:17 UTC, Whoey Louie wrote:
>>
>> A couple of years ago I helped choose colours for the input connectors
>> of a networking product that had 12V (automotive range) and 48V
>> versions. The 12V choice was easy. We were using Anderson Powerpole
>> connectors, so we followed the amateur radio convention for these
>> connectors with red for positive and black for negative in a specific
>> configuration.
>> For 48V, I looked at every standard I could find and found a mass of
>> conflicting recommendations. An additional constraint was that we wanted
>> to use the "finger safe" version of the connectors and could only use
>> colours available from Anderson. Most customers would use positive
>> ground, but some had negative ground systems.
>> The final outcome was that the input was isolated with no connection
>> between either power terminal and chassis and the positive terminal
>> was red and the negative terminal was blue. This seemed to be in keeping
>> with the spirit of most of the standards and less likely to cause
>> confusion than any other combination.
>> Pictures at the bottom of the page:
>> https://www.firebrick.co.uk/fb2900/
>

> That's what I would have done too. I sure would not use red for negative
> and black for positive. I was thinking about saying in the other reply
> that if I decided to use black for the return in a positive ground system,
> then I sure would not use red for the supply. I would use some other
> color that would at least give someone looking at it reason to further
> look into what's going on. When one sees just red and black in low
> voltage DC system, one naturally assumes red is positive.

This schematic shows red assigned to the higher potential and black
assigned to the lower, more negative, potential:

https://resources.secamerica.com/hs-fs/hubfs/Blog_Images/48vdc_for_telecom.jpg

Red is assigned to the relatively positive power rail, at least in this
schematic. What installers choose to do in the field's a whole nother
story.

That schematic originates with communications vendor:

https://www.secamerica.com/applications/communications/

Presumably the vendor knows more than most about color code usage in
the industry.

In regards to ground:

"Ground is a fantasy invented by engineers to simply
their work." - Bill Whitlock

The ground fantasy as applied to this thread seems to complicate instead
of simplify. It's probably best to leave it out.

Thank you,

--
Don Kuenz KB7RPU
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.

[Whoey Louie]

On Tuesday, January 28, 2020 at 2:50:00 PM UTC-5, whit3rd wrote:
> On Tuesday, January 28, 2020 at 10:56:17 AM UTC-8, Whoey Louie wrote:
>
> > ... I agree, it is
> > confusing. I would not expect red to be the negative supply side and
> > black to be positive. That is confusing and asking for trouble.
>
> Alas, the innards of an automobile won't teach you anything bur red = positive.
> There are LOTS of color conventions, many with legal enforcement, and
> one must learn not to generalize.
>
> In US house wiring, red would be AC high voltage.

If you mean by high voltage 240/120 AC then yes that's true, red
could be used. But Grant's example is DC and 48V. You could also have
red and black in house wiring in other applications, eg HVAC,thermostats,
alarm wiring. But red for positive and black for negative in DC was
the issue and this is the first application where I've heard of red
being used for neg, black for positive.

In a computer, red is +5V,
> and yellow is +12V.

In every low voltage DC anything where there is just one voltage, I've
never seen red and black be anything other than positive and negative.
Apparently it exists, but it's not common and the convention is not
limited to cars. Buy a DC, low voltage, one speed motor, I've
never seen one where red and black did not mean pos and neg, have you?

[Whoey Louie]

I'm wondering what color was used on the negative/supply side of the
wiring in early cars that used a positive ground? I took a quick
google, couldn't find anything.

>
> In regards to ground:
>
> "Ground is a fantasy invented by engineers to simply
> their work." - Bill Whitlock
>
> The ground fantasy as applied to this thread seems to complicate instead
> of simplify. It's probably best to leave it out.

Earth ground, I would agree is just a further complication here.
But ground in general is just a system reference point and typically
the return. So if someone was working on Grant's system and hooked
a meter between -48V wiring and the return wiring, it would be common
to say that he's measuring between supply and ground.

[DecadentLinux...@decadence.org]

whit3rd <whi...@gmail.com> wrote in
news:d571a9c6-95b9-4c45...@googlegroups.com:

We designed a negative HV supply. While we would typically all
agree that black is ground, we all know that ground is not always
negative. It is most commonly always BLACK, however (AC fault return
wires do not count).

So our negative supply had a RED "HOT" wire and black was ground.
Being an isolated supply it should not matter. The signal to the
user is that red is HOT, not neccessarily positive.

[DecadentLinux...@decadence.org]

Whoey Louie <tra...@optonline.net> wrote in news:499044a5-a46d-45a0-
afbb-698...@googlegroups.com:

> I'm wondering what color was used on the negative/supply side of the
> wiring in early cars that used a positive ground? I took a quick
> google, couldn't find anything.
>
>

6 Volt automotive systems used black cables throughout.
Many used terminated bare braided tinned copper cable for the grounded
side.

[DecadentLinux...@decadence.org]

DecadentLinux...@decadence.org wrote in
news:r0q8qe$1ivm$1...@gioia.aioe.org:

Aftermarket replacements, however, are colored red for positive
side connections.

Lots of stuff about converting old Willys jeeps to negative ground.

Some folks are simply confused when things do not match their pre-
conceived ideas.

[Whoey Louie]

On Tuesday, January 28, 2020 at 2:22:16 AM UTC-5, Rick C wrote:

> On Monday, January 27, 2020 at 11:20:11 PM UTC-5, Grant Taylor wrote:
> > On 1/27/20 8:17 PM, Rick C wrote:
> > > Positive and negative are electrical terms of physics. It has nothing
> > > to do with convention of colors or which polarity of common you use.
> > > Connect the positive meter probe to the positive power line and you
> > > will always measure a positive voltage no matter what.
> >
> > Presuming the negative meter probe is connected to negative power line,
> > and I agree.
> >
> > The thing that I've learned is that there is no correlation between
> > "hot" / "common" / "return" / "ground" with positive or negative like I
> > have naively thought for the last 30 years.
>
> That's because positive ground systems are the exception rather than the norm. Telephony related gear is an exception... when powered from 48 volts, but not always even then. I have seen gear that didn't have an internal connection to common and so could be used as positive ground or negative ground.
>
>
> > > That would imply the equipment cabinet be grounded and the equipment
> > > connected to that. The power source can be floating and the equipment
> > > should not care. Do the equipment vendors define "properly grounded",
> > > that is, any specific instructions?
> >
> > Yes. The better documentation calls out very specific directions on how
> > to bond ground to the equipment. They are quite specific about earth /
> > safety ground.
> >
> > > Is this strap at the power supply or the equipment being powered?
> >
> > It is part of part of the power supply.
>
> That surprises me a bit. A AC/DC power supply output is typically isolated from the input power line, so common is whichever terminal you connect to... common. Having a connection internally to the AC protective earth limits the applications with no added advantage.

It it's a power supply supplied by the same company that makes the
gear it's connected to, or intended specifically for the application
it's being used in, they don't give a rat's ass about how it might
be used for something else. It's not a bench power supply.

[upsid...@downunder.com]

On Tue, 28 Jan 2020 11:49:56 -0800 (PST), whit3rd <whi...@gmail.com>
wrote:

>In US house wiring, red would be AC high voltage. In a computer, red is +5V,
>and yellow is +12V. In European AC cables, black is neutral, but in US
>the white is neutral. Ground is sometimes black, sometimes green, and
>green/yellow stripe is almost always ground.

In AC wiring in Europe, light blue is neutral, green/yellow stripe is
the protective earth (PE). It is forbidden to use the green/yellow
stripe for anything else than ground/earh. If you are forced to use
some other colord conductor for PE, the ends must be marked with
green/yellow stripe tape.

[jrwal...@gmail.com]

Just to confuse things even more, the live wires in 3 phase systems
in Europe (including UK) are brown, black and grey. The old UK colours
were black for neutral and red, yellow and blue for the phases. There
are many installations where both sets of colours are mixed!
John

[sea moss]

> I suspect that there is more to it than simply reversing the + and -
> lead from a battery or meter. But I can't wrap my head around it.

I think it may become crystal clear for you if you can visualize what a negative voltage is, and how the currents flow.

For me, the water analogy helped me visualize it. Think of a voltage source (power supply output) as a water pump, which brings water uphill to a reservoir. So a +10V supply is like pumping water up a 10 foot wall. Then when you connect to a load, that is like dropping the water (kinetic energy); it returns to ground and has no energy left so you continue to pump it uphill. Currents only flow downhill.

Now for the -10V supply, dig a 10 foot hole and put the pump from the bottom of the hole to ground level. Now you connect to a load the same way as before, you drop the water down into the hole (kinetic energy) and then you pump it back up. Currents continue to only flow downhill.

If you have a power supply with +10V and ground outputs, you can measure the current, it will always flow out the +10V and back on the ground terminal. If your power supply has -10V and ground output, the current will flow out the ground output and return on the -10V.

It sounds like your systems use black=ground and red=hot, whether red is negative or positive. "Hot" is a good term, since current will flow through your body if you touch the red wire and you are grounded. Only difference for a negative voltage is the direction the current takes as it flows through you.

[Grant Taylor]

On 1/28/20 2:37 PM, DecadentLinux...@decadence.org wrote:
> Some folks are simply confused when things do not match their

> preconceived ideas.

I think it's fair to say that I was. Hence why I started this thread.

I feel like I've gained a better understanding of what's going on.

[Grant Taylor]

On 1/28/20 4:18 PM, jrwal...@gmail.com wrote:
> Just to confuse things even more, the live wires in 3 phase systems in
> Europe (including UK) are brown, black and grey. The old UK colours
> were black for neutral and red, yellow and blue for the phases.
> There are many installations where both sets of colours are mixed!

Oy vey!

And I thought old four pair phone wire color codes and new four pair
phone wiring color codes were confusing / annoying, in that they take a
few minutes to stop, think about, and figure out. But that is nominally
low voltage and decidedly low current. Much less room for catastrophic
failure than the old & new color codes for three phase.

[Grant Taylor]

I'd like to take a moment to thank everybody that has helped me along my
journey to learn about Negative 48 Volts DC. I believe that I have
learned, and unlearned, enough to have a acceptable decent understanding.

I have learned that the terms "hot" / "common" / "return" / "ground" do
not correlate with the polarity without indication of "negative ground"
(what I'm used to) or "positive ground".

In a negative ground system, the "hot" wire will be positive compared to
"ground" / "return".

In a positive ground system, the "hot" wire will be negative compared to
"ground" / "return".

[John Larkin]

If you want to measure the height of something, you need to stand
somewhere and call that "zero." There is such a thing as absolute sea
level, H=0, and electrical earth ground, V=0, but they may not always
be available.

So we clip the "negative" (better called the "reference") wire of a
voltmeter to something conductive and declare that to be "ground",
namely zero volts. Chassis, car body, metal ladder that we're standing
on, most anything. Then we measure positive or negative voltages
relative to that.

We have one Tek oscilloscope with fully isolated channels. We can clip
a scope probe ground to the hot side of the AC line and then probe
relative to that.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com