Variac question

[Ivan Vegvary]

Purchased used Variac. Good action, very smooth from 0 to 140V AC.
Question: Input and output are both 2 prong, no ground. Should I modify it to three prong with ground?
BTW, I do also own a functioning isolation transformer.
Should the IXformer be placed between the mains and the Variac? Please advise as to best procedure. Thanks. Main use of Variac will be to power up ancient tube equipment.
Thank you!

[John Robertson]

As long as the variac passes basic eletrical leakage test fine and the
powre cord and internal wiring are in good condition there is little
sense in trying to upgrade it to three conductor wiring.

In fact I recall reading somewhere (can't find the link) that it is
against the electrical safety regulations to convert two conductor
products to three conductor. This could be incorrect, until I can find
the reference take it with a grain of salt. However many items wired for
two conductor would need to be modified for three conductor beyond just
adding a ground - in pinball and jukeboxes the older two conductor items
correctly had the power switch on one side of the line and the line fuse
on the other - this is totally wrong on three wire setups!

So use the isolation Xformer to be safe.

Also, I trust you are aware of the series lamp (25 to 100W bulb
depending on the load) test for powering up gear that you aren't sure
hasn't a problem (shorted winding, cap, rectifier, etc.)...

John :-#)#
--
(Please post followups or tech inquiries to the USENET newsgroup)
John's Jukes Ltd.
MOVED to #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3
(604)872-5757 (Pinballs, Jukes, Video Games)
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"Old pinballers never die, they just flip out."

[Phil Allison]

John Robertson wrote:

>
>
> As long as the variac passes basic eletrical leakage test fine and the
> powre cord and internal wiring are in good condition there is little
> sense in trying to upgrade it to three conductor wiring.
>

** To maintain the safety of equipment that normally uses a ground conductor with a 3 pin plug - earth continuity must remain intact.

> In fact I recall reading somewhere (can't find the link) that it is
> against the electrical safety regulations to convert two conductor
> products to three conductor.
>

** If the product as originally sold was of Double Insulated (aka class2) design, this may be true. Earthing a Class 2 shaver is silly.

But I would not hesitate to add a 3 conductor cable to any guitar amp, powered desk or similar I found that did not have it.

> This could be incorrect, until I can find
> the reference take it with a grain of salt. However many items wired for
> two conductor would need to be modified for three conductor beyond just
> adding a ground - in pinball and jukeboxes the older two conductor items
> correctly had the power switch on one side of the line and the line fuse
> on the other - this is totally wrong on three wire setups!
>

** Sounds easy enough to correct, as it is to remove the infamous "death cap" fitted to many 2 wire guitar amps not so long ago.



.... Phil

[Phil Allison]

Ivan Vegvary wrote:
>
>
> Purchased used Variac. Good action, very smooth from 0 to 140V AC.
>
> Question: Input and output are both 2 prong, no ground.
> Should I modify it to three prong with ground?
>

** Yes - all modern ones are made like that. It is not safe to de-earth an appliance just because you need to use a Variac with it.

> BTW, I do also own a functioning isolation transformer.
> Should the IXformer be placed between the mains and the Variac?
> Please advise as to best procedure.
>

** Either way works, feeding 140VAC to the Iso may get it a bit hot though.

> Main use of Variac will be to power up ancient tube equipment.

** I use mine for almost everything.

Cos I hate blowing fuses at switch-on.


.... Phil

[tabb...@gmail.com]

On Saturday, 3 November 2018 04:43:21 UTC, Ivan Vegvary wrote:

> Purchased used Variac. Good action, very smooth from 0 to 140V AC.
> Question: Input and output are both 2 prong, no ground. Should I modify it to three prong with ground?

it's safer to

> BTW, I do also own a functioning isolation transformer.
> Should the IXformer be placed between the mains and the Variac? Please advise as to best procedure. Thanks. Main use of Variac will be to power up ancient tube equipment.
> Thank you!

that works, but don't assume you won't then get a shock from a live wire. Safer & easier now to use an RCD/GFCI.


NT

[Cursitor Doom]

On Fri, 02 Nov 2018 21:43:18 -0700, Ivan Vegvary wrote:

> Purchased used Variac. Good action, very smooth from 0 to 140V AC.
> Question: Input and output are both 2 prong, no ground. Should I modify
> it to three prong with ground?

I certainly would.

> BTW, I do also own a functioning isolation transformer.
> Should the IXformer be placed between the mains and the Variac? Please
> advise as to best procedure. Thanks. Main use of Variac will be to
> power up ancient tube equipment.
> Thank you!

The isolation transformer should always power the *device under test* to
remove the Earth reference from it.




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protocols constitutes acceptance of this condition.

[Ralph Mowery]

In article <X-WdneIGd9CSrUDG...@giganews.com>,
sp...@flippers.com says...

>
> In fact I recall reading somewhere (can't find the link) that it is
> against the electrical safety regulations to convert two conductor
> products to three conductor. This could be incorrect, until I can find
> the reference take it with a grain of salt. However many items wired for
> two conductor would need to be modified for three conductor beyond just
> adding a ground - in pinball and jukeboxes the older two conductor items
> correctly had the power switch on one side of the line and the line fuse
> on the other - this is totally wrong on three wire setups!
>
>

In just the last few years I have been looking at the older equipment (
some in the mid 1960s) and they were 2 wire devices. They had the
switch on one side of the transformer and the fuse on the other side. I
don't know about the code or why it was done that way. I would have
thought the fuse would come first on the hot wire and then the switch.
Much of the equipment is ham radio related and most users would have a
good connection of the chassis to the earth ground.

[Fox's Mercantile]

On 11/3/18 9:37 AM, Ralph Mowery wrote:
> In just the last few years I have been looking at the older equipment

> (some in the mid 1960s) and they were 2 wire devices. They had the

> switch on one side of the transformer and the fuse on the other side.
> I don't know about the code or why it was done that way. I would have
> thought the fuse would come first on the hot wire and then the switch.
> Much of the equipment is ham radio related and most users would have a
> good connection of the chassis to the earth ground.

Because in the end, it's a series circuit. It doesn't make a damn bit of
difference.

Primarily, it was done from a "Is this the cheapest and easyist (also
cheapest) way to do it this way?"




--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

[Ivan Vegvary]

Thank you everybody. Great help! Will always use the isolation xformer

[Cursitor Doom]

On Sat, 03 Nov 2018 10:38:54 -0700, Ivan Vegvary wrote:

> Thank you everybody. Great help! Will always use the isolation xformer

One last thing: don't ever get into the habit of using that variac of
yours as a convenient substitute for an extension lead.
Enjoy!

[tabb...@gmail.com]

It makes a huge difference.
Fuse in live blown: faulty equipment is now dead.
Fuse in neutral blown: faulty equipment looks dead but is live.
One can electrocute you after a live to case fault, the other won't.
This is why UK banned dual pole mains fusing in 1955.


NT

[Phil Allison]

Ivan Vegvary wrote:
>
>
> Thank you everybody.
> Great help! Will always use the isolation xformer
>
>

** Who here said to do that ???

Good safety practice is to use an isolation ONLY when you need to - as with old live chassis radios or off-line SMPUs.

Never disconnect your scope from safety earth and if equipment on test has the safety ground connected to the chassis - leave it that way.



.... Phil

[Ralph Mowery]

In article <839ff2eb-6ef5-4f76...@googlegroups.com>,
tabb...@gmail.com says...

>
> It makes a huge difference.
> Fuse in live blown: faulty equipment is now dead.
> Fuse in neutral blown: faulty equipment looks dead but is live.
> One can electrocute you after a live to case fault, the other won't.
> This is why UK banned dual pole mains fusing in 1955.
>
>
>

Ideas and codes change from one country to the next and sometimes even
in the same country.

In my opinion one of the worst things was some equipment where aI
worked. The standard in the US was that on electrical equipment boxes
red was off and green was on. We got in some equipment from Europe and
they used Green for off and Red for on. The reason being that Green was
safe to open the door and red ment power was on and danger.


I know that in a series circuit that electrically it does not matter in
which order things are for them to work. I was just courious that much
of the older two wire 120 volt stuff that has a transformer , the power
comes in, then a switch, transformer primary , fuse and back out to the
power. I would have thought it would be the power, fuse, switch,
transformer and back out to power.

[tabb...@gmail.com]

On Sunday, 4 November 2018 03:58:17 UTC, Ralph Mowery wrote:
> In article <839ff2eb-6ef5-4f76...@googlegroups.com>,
> tabbypurr says...

The only justification I can think of for the old practice of putting the switch & fuse in different leads for unpolarised kit is the idea that the switch is a relative weakpoint, so would likely act as a higher current fuse if there were a short from live to some good earth - not good but better than nothing. I suppose it's also marginally easier for production to have 2 things to solder the mains wires to.


NT

[Cursitor Doom]

On Sat, 03 Nov 2018 23:58:08 -0400, Ralph Mowery wrote:

> In my opinion one of the worst things was some equipment where aI
> worked. The standard in the US was that on electrical equipment boxes
> red was off and green was on. We got in some equipment from Europe and
> they used Green for off and Red for on. The reason being that Green was
> safe to open the door and red ment power was on and danger.

And just to further complicate matters, in domestic consumer units
nowadays, the spur is live when the switch is in the 'up' position and
'off' is down. This is arse-about-face to what I - at least - was brought
up with in the UK. :(

[Ralph Mowery]

In article <prmice$bk8$3...@dont-email.me>, cu...@notformail.com says...

>
> And just to further complicate matters, in domestic consumer units
> nowadays, the spur is live when the switch is in the 'up' position and
> 'off' is down. This is arse-about-face to what I - at least - was brought
> up with in the UK. :(
>
>
>

I live in the US. I don't know if it the code or not, but just about
all the light switches and many other types that work up and down, the
up is on and the down is off.

From what I have heard in the UK up is off and down is on for house
light switches.

I only have a couple of things around the house that have vertical
switches. The ones from China are up for on, but one from Japan is down
for on. Most everything else is push button and that is push in for on
if the switch stays in. On some the pushbutton just returns to the out
position.

[Mike Coon]

In article <MPG.3648dff86...@news.east.earthlink.net>,
rmower...@earthlink.net says...

>
> From what I have heard in the UK up is off and down is on for house
> light switches.

Yes, power outlets too; pretty general default. But I was aware (having
visited several times) that USA was opposite. Maybe something to do with
driving on left or right?

Mike.

[Roger Blake]

On 2018-11-04, Ralph Mowery <rmower...@earthlink.net> wrote:
> From what I have heard in the UK up is off and down is on for house
> light switches.

What else would you expect from people who inist upon driving on the
wrong side of the road? (At least the Swedes wised up in the 1960s.)

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[gregz]

I would place ISO XFMR after variac. The transformer is not 1:1 and
designed to be 1:1 under full load. Depends on current either way you can
end up say 160 volts no load.

Greg

[gregz]

There are different types of isolation transformers. The ones many sell in
US with outlets and all, have three prong grounded outlets, and that groung
is tied to one leg of output forming new neutral. These are specific for
reducing noise. No ground isolation.

Greg

[three_jeeps]

On Wednesday, November 7, 2018 at 3:39:07 AM UTC-5, GS wrote:

I can't advise on the modification to connect the variac to earth ground. One would have to know the design of the variac to accomplish this safely, if indeed it is a good idea at all. IMHO, I would not modify the autotransformer. One need to be aware of the 'upstream' power distribution network. In the states, residential customers are fed by three wire split phase distribution transformer that sits on a power pole or power utility box. The 120 VAC power is between ground and one half of the phase winding.

I would also place the isolation xfmr after the variac. Variac (short for variable autotransformer) is an interesting device in that there is no isolated secondary winding. A portion of the primary winding serves as a secondary. There are taps along the primary winding that allow for stepping up or down the output voltage.
One can use a variac for: reforming power supply capacitors in equipment that has been sitting idle for a number of years, testing the tolerance of electronic equipment/designs to under/over voltage conditions, gradually increasing the voltage to equipment to avoid 'shock' of the components, dimming incandescent light bulbs, and testing dropout of electronic devices under low voltage conditions. We used variacs to lower the supply voltage to computers to prove that the machines we designed would function down to at least 80% of line voltage, and when a threshold was hit, the machine would gracefully shutdown in x milliseconds. It was a requirement of the system.

Isolation transformer are used a lot in servicing certain type of electronic equipment (e.g. tube TVs, amplifier, radio transmitters, etc.). It removes the direct path to ground of the electrical power, significantly reducing the chance of death. Ask any service tech or engineer who has seen their scope probe or DMM probe almost vaporize when the accidentally probe a circuit that effectively causes a path to ground through the probe.

good luck
J

[peterw...@gmail.com]

RANT WARNING:

Isolation transformers are critical for any workbench, and after good
hand-tools the first thing any radio person should get... perhaps even
before said tools.

Variacs, on the other hand, are either very handy diagnostic tools or
worse-than-useless anchors fit only to let the magic smoke out of an
otherwise salvageable radio. I am not really sure if there is an in-between
other than their original function as light dimmers.

Without both current and voltage metering, they are worse-than-
useless. With the proper metering, they can be very handy tools.

Myths: A variac will help reform caps (with specific reference to tube/
valve radios).

Fact: Only on those vanishingly few radios with solid-state rectifiers
that pass B+ current at any voltage, and only if done over more time than
one cares to consider. Bench DC supplies are best for this typically futile
purpose in any case.

In the case of a tube rectifier, most of them do not start to pass DC
until the filament voltage reaches between 65% and 75% of nameplate rating. If the B+ on the particular radio is say.... 350V, that means that the first voltage the caps-to-be-reformed would see would be something between 227V and 263V... not exactly a soft-start.

Myth: A variac will allow one to apply voltage gently to a radio, so
as to discover problems before they become fatal.

Fact: No, not at all. True, a variac does allow a radio to see the
minimum amount of current to trigger its functions... an AA5 with bad filter
caps may begin to hum at 80V rather than 120V, similarly with a transformer
radio. But if the caps are not so bad as to show audible hum, the variac ceases to be useful. And a variac will *not* tell you whether a repaired radio is OK or not.

However, if the proper meters are put on the Isovariac, then some
real diagnosis can happen: An AA5 which should, by calculation draw say...
35 watts or so (0.3A), and draws 42 watts is dissipating 7 watts of heat
somewhere... perhaps the output transformer. And, unless one has calibrated
eyeballs, the difference of 7 watts will not show up on a dim-bulb tester.

Comes down to a current meter with fine enough increments to give
meaningful information. Such a tool is useful right down the line from initial diagnosis to testing the completed results.

End Rant. And it could have been much longer.

As to order-of-parts:
I keep the Heathkit IP 5220 (this one: http://www.byan-roper.org/steve/steve-at-play/antique-electronics-and-2/heathkit-ip-5220-variable.html )

From what you are seeing, it is pretty clear that the Iso goes after the Variable in this design.

Peter Wieck
Melrose Park, PA

[tabb...@gmail.com]

On Wednesday, 7 November 2018 18:20:10 UTC, pf...@aol.com wrote:

> RANT WARNING:

> Myths: A variac will help reform caps (with specific reference to tube/
> valve radios).
>
> Fact: Only on those vanishingly few radios with solid-state rectifiers
> that pass B+ current at any voltage, and only if done over more time than
> one cares to consider. Bench DC supplies are best for this typically futile
> purpose in any case.
>
> In the case of a tube rectifier, most of them do not start to pass DC
> until the filament voltage reaches between 65% and 75% of nameplate rating. If the B+ on the particular radio is say.... 350V, that means that the first voltage the caps-to-be-reformed would see would be something between 227V and 263V... not exactly a soft-start.

Not so. The trick is to meter the B+ and wind the variac up uberslowly around the point when the rectifier begins to conduct. That way the rectifier passes only tiny current and you can indeed wind the B+ up from close to nothing. BTDT. Of course there may be easier ways now.

It's true that their uses are very few nowadays. But marginally more than zero.


NT

[peterw...@gmail.com]

On Wednesday, November 7, 2018 at 2:02:27 PM UTC-5, tabb...@gmail.com wrote:

> Not so. The trick is to meter the B+ and wind the variac up uberslowly around the point when the rectifier begins to conduct. That way the rectifier passes only tiny current and you can indeed wind the B+ up from close to nothing. BTDT. Of course there may be easier ways now.
>
> It's true that their uses are very few nowadays. But marginally more than zero.

Rectifiers are go/no-go devices.
Variacs are not current-limiting devices.
The voltage a (tube) rectifier passes will be a function of the minimum trigger voltage on the filament as a percentage of the "correct" filament voltage x the "correct" B+ voltage. So, if the rectifier filament trigger voltage is 4 V vs. the nominal 5 V (80%), then the passed voltage will be nominal B+ x 0.80. There is no 'winding' up.

This is the same argument as "just a little bit pregnant". The logic is just as faulty.

[Ralph Mowery]

In article <34d141f2-f78f-4309...@googlegroups.com>,
peterw...@gmail.com says...

>
> Myths: A variac will help reform caps (with specific reference to tube/
> valve radios).
>
> Fact: Only on those vanishingly few radios with solid-state rectifiers
> that pass B+ current at any voltage, and only if done over more time than
> one cares to consider. Bench DC supplies are best for this typically futile
> purpose in any case.
>
> In the case of a tube rectifier, most of them do not start to pass DC
> until the filament voltage reaches between 65% and 75% of nameplate rating. If the B+ on the particular radio is say.... 350V, that means that the first voltage the caps-to-be-reformed would see would be something between 227V and 263V... not exactly a soft-start.
>
>
>

There is a 'more correct way" to do the reforming if one wants to try.
If a tube rectifier you pull that tube or tubes and install solid state
rectifiers. Then pull the other tubes to prevent cathode stripping.

Most electrolytic capacitors are formed at the factory at about 10 % or
so over the rated voltage. As they sit on the shelf they will degrade
somewhat. It sometimes makes sense to reform even new ones if they have
been on the shelf for many years. That is where a bench supply comes in
handy.

I wish I could find the magazine I had around 1965 give or take a few
years. In it was an automatic restorer. I think it used a bunch of
neon lights, but could be wrong. It may have been Electronics
Illistrated. Don't think it was Popular Electronics. Maybe Radio
Electronics.

[tabb...@gmail.com]

On Wednesday, 7 November 2018 19:13:17 UTC, pf...@aol.com wrote:

> On Wednesday, November 7, 2018 at 2:02:27 PM UTC-5, tabby wrote:
>
> > Not so. The trick is to meter the B+ and wind the variac up uberslowly around the point when the rectifier begins to conduct. That way the rectifier passes only tiny current and you can indeed wind the B+ up from close to nothing. BTDT. Of course there may be easier ways now.
> >
> > It's true that their uses are very few nowadays. But marginally more than zero.
>
> Rectifiers are go/no-go devices.

valve rectifiers are not. The current they pass depends on filament temperature/voltage.

> Variacs are not current-limiting devices.

they are voltage controllers. The rectifier is a current controller when run undervolted.

> The voltage a (tube) rectifier passes will be a function of the minimum trigger voltage on the filament as a percentage of the "correct" filament voltage x the "correct" B+ voltage. So, if the rectifier filament trigger voltage is 4 V vs. the nominal 5 V (80%), then the passed voltage will be nominal B+ x 0.80. There is no 'winding' up.

I'm not at all clear about your argument, but they certainly do wind up on a variac. I've done it.

> This is the same argument as "just a little bit pregnant". The logic is just as faulty.
>
> Peter Wieck
> Melrose Park, PA

Try it some time. You'll find out what you got wrong.


NT

[Fox's Mercantile]

I have a large (20 amp) Sola harmonically balanced constant
voltage transformer. I cut the neutral common and use a SPDT
center off switch, so I can select Utility Neutral, floating
(i.e. isolation) and Local Neutral (tied to the ground at
the transformer.)

Following that I have a 20 amp Variac, that I can wind up
from 0-132 VAC. With a 2-5-10 selectable amp meter.

Finally, a custom 4-terminal dynamic watt meter. 0-1500 watts.

What do I use it for? Very rarely.
The time I used it was to test the applied voltages on some
1947 to 1959 boat anchors to see "just how much over voltage"
they were at 125 vac line vs 110 vac line voltages.

Solution? Using a 5-10 amp filament transformer in the buck
mode to drop the line voltage back down to 115 vac.

Do I waste my time reforming capacitors? No. And certainly
NOT in customer equipment. Saving $5-20 on a repair is NOT
worth a warranty repair.

Sure, I'll fix it for free, but my reputation takes a hit.
"Why didn't you fix it right to begin with?"
Apparently, "because I was lazy" is not an appropriate answer.

[Phil Allison]

three_jeeps wrote:

>
>
> Isolation transformer are used a lot in servicing certain type of
> electronic equipment (e.g. tube TVs, amplifier, radio transmitters, etc.).
>

** But only those examples where the items have no AC supply isolation transformers - IOW they are *HOT CHASSIS* designs. All of them very old and very obsolete.

Contemporary use of 1:1 isolation transformers would be for servicing devices like SMPSs.

> It removes the direct path to ground of the electrical power,
> significantly reducing the chance of death.

** That is wrong.

Using an isolation transformer allows one to connect the common rail ( or any other point) of an off-line SMPS to safety ground. After which you can use a scope in the normal way to investigate various waveforms, maybe small ones like MOSFET drive signals.



.... Phil

[tabb...@gmail.com]

On Thursday, 8 November 2018 02:20:42 UTC, Phil Allison wrote:
> three_jeeps wrote:
>
> >
> >
> > Isolation transformer are used a lot in servicing certain type of
> > electronic equipment (e.g. tube TVs, amplifier, radio transmitters, etc.).
> >
>
> ** But only those examples where the items have no AC supply isolation transformers - IOW they are *HOT CHASSIS* designs. All of them very old and very obsolete.

Well, they were standard & widespread in the 1990s.

> Contemporary use of 1:1 isolation transformers would be for servicing devices like SMPSs.
>
>
> > It removes the direct path to ground of the electrical power,
> > significantly reducing the chance of death.
>
> ** That is wrong.
>
> Using an isolation transformer allows one to connect the common rail ( or any other point) of an off-line SMPS to safety ground. After which you can use a scope in the normal way to investigate various waveforms, maybe small ones like MOSFET drive signals.

One can, but they are also used to reduce shock risk.


NT

[Phil Allison]

tabb...@gmail.com wrote:

>
> Phil Allison wrote:
>
> >
> > >
> > >
> > > Isolation transformer are used a lot in servicing certain type of
> > > electronic equipment (e.g. tube TVs, amplifier, radio transmitters,
> > >
> >

> > ** But only those examples where the items have no AC supply isolation
> > transformers - IOW they are *HOT CHASSIS* designs. All of them very old
< and very obsolete.
>
> Well, they were standard & widespread in the 1990s.
>

** Live chassis tube TVs and radios " standard & widespread " in the 1990s ????

FYI:

The OP did NIT even mention "live chassis" so his post was wrong and so is yours.

> > Contemporary use of 1:1 isolation transformers would be for
> > servicing devices like SMPSs.
> >
> >
> > > It removes the direct path to ground of the electrical power,
> > > significantly reducing the chance of death.
> >
> > ** That is wrong.
> >
> > Using an isolation transformer allows one to connect the common
> > rail ( or any other point) of an off-line SMPS to safety ground.
> > After which you can use a scope in the normal way to investigate
> > various waveforms, maybe small ones like MOSFET drive signals.
>
>
> One can, but they are also used to reduce shock risk.
>

** Biggest safety myth out.

Using an isolation transformer unnecessarily INCREASES electric shock risk.



.... Phil

[tabb...@gmail.com]

On Thursday, 8 November 2018 06:37:49 UTC, Phil Allison wrote:

> tabby wrote:
> > Phil Allison wrote:

> > > > Isolation transformer are used a lot in servicing certain type of
> > > > electronic equipment (e.g. tube TVs, amplifier, radio transmitters,
> > > >
> > >
> > > ** But only those examples where the items have no AC supply isolation
> > > transformers - IOW they are *HOT CHASSIS* designs. All of them very old
> < and very obsolete.
> >
> > Well, they were standard & widespread in the 1990s.
>
> ** Live chassis tube TVs and radios " standard & widespread " in the 1990s ????

Live chassis TVs were very common in the 90s. Live chassis radios disappeared in the 60s.

> FYI:
>
> The OP did NIT even mention "live chassis" so his post was wrong and so is yours.

I was responding to your mention of 'hot chassis' not the OP's. What the OP mentioned is irrelevant.

> > > Contemporary use of 1:1 isolation transformers would be for
> > > servicing devices like SMPSs.
> > >
> > >
> > > > It removes the direct path to ground of the electrical power,
> > > > significantly reducing the chance of death.
> > >
> > > ** That is wrong.
> > >
> > > Using an isolation transformer allows one to connect the common
> > > rail ( or any other point) of an off-line SMPS to safety ground.
> > > After which you can use a scope in the normal way to investigate
> > > various waveforms, maybe small ones like MOSFET drive signals.
> >
> >
> > One can, but they are also used to reduce shock risk.
> >
>
> ** Biggest safety myth out.
>
> Using an isolation transformer unnecessarily INCREASES electric shock risk.

The UK government certainly disagrees with you. We have used isolation transformers for decades in bathrooms to reduce shock risk. Of course you're free to explain your pov.


NT

[peterw...@gmail.com]

One of the things you will learn about Phil is that he suffers from a congenital fixation with the fallacy of illicit transference - meaning that what is true of the parts is true of the whole. My cat is grey, therefore all cats are grey (apologies to Ben Franklin).

There are unique conditions in which an isolation transformer does not prevent the risk of electric shock. Therefore they increase the risk of electric shock.

Idiots will find a way to solve for the most idiot-proof safety measures as conceived, because they were not conceived by idiots. And if one inserts one's self into an electrical circuit, one will be shocked.

If you want to twist the dragon's tail, just get Phil started on newly-made multi-section can-caps.

[tabb...@gmail.com]

I know he's a character. Some things he understands well, but no-one gets everything right.

I've put myself into an electrical circuit numerous times without getting shocked.


NT

[peterw...@gmail.com]

I've put myself into an electrical circuit numerous times without getting shocked.... that I remember.

[Jeff Liebermann]

On Thu, 8 Nov 2018 09:50:30 -0800 (PST), tabb...@gmail.com wrote:

>I've put myself into an electrical circuit numerous times without getting shocked.
>NT

Were you wearing a Faraday cage or chain mail armor suit?
<https://esfstream.com/faraday-cage-suit/>
<https://www.flickr.com/photos/stevencaton/sets/72157631825725155/>

I haven't been zapped since tubes and hi-v were displaced by lower
voltage transistors. I've gotten my share of RF burns, but those
don't count as getting shocked.

--
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

[John-Del]

On Thursday, November 8, 2018 at 3:38:08 PM UTC-5, Jeff Liebermann wrote:


....I've gotten my share of RF burns, but those

> don't count as getting shocked.
>

Sure they do. It's different in that you get a shock that can burn right to the bone and cauterize itself so it doesn't bleed. Got lots of those. Yep, good times.

Still get whacked mostly by power supplies that hold 400V across the PFC cap for a couple of days. Those will get your attention.

[tabb...@gmail.com]

On Thursday, 8 November 2018 20:38:08 UTC, Jeff Liebermann wrote:

> On Thu, 8 Nov 2018 09:50:30 -0800 (PST), tabbypurr wrote:

> >I've put myself into an electrical circuit numerous times without getting shocked.

> Were you wearing a Faraday cage or chain mail armor suit?
> <https://esfstream.com/faraday-cage-suit/>
> <https://www.flickr.com/photos/stevencaton/sets/72157631825725155/>

No. I might go & connect myself to 10,000v tonight :)

[Phil Allison]

tabb...@gmail.com wrote:
>
> Phil Allison wrote:
> >

> > >

> > > Well, they were standard & widespread in the 1990s.
> >
> > ** Live chassis tube TVs and radios " standard & widespread " in the 1990s ????
>
> Live chassis TVs were very common in the 90s.

** But not TUBE sets as the above requires.

I have a 1990s 12 inch GE color portable where the whole chassis is live and only isolated by the antenna balun.

> > FYI:
> >
> > The OP did NIT even mention "live chassis" so his post was wrong and so is yours.
>
> I was responding to your mention of 'hot chassis' not the OP's.
> What the OP mentioned is irrelevant.
>

** Bullshit. I was responding to the OP post - so what he wrote is totally relevant.

> > > > Contemporary use of 1:1 isolation transformers would be for
> > > > servicing devices like SMPSs.
> > > >
> > > >
> > > > > It removes the direct path to ground of the electrical power,
> > > > > significantly reducing the chance of death.
> > > >
> > > > ** That is wrong.
> > > >
> > > > Using an isolation transformer allows one to connect the common
> > > > rail ( or any other point) of an off-line SMPS to safety ground.
> > > > After which you can use a scope in the normal way to investigate
> > > > various waveforms, maybe small ones like MOSFET drive signals.
> > >
> > >
> > > One can, but they are also used to reduce shock risk.
> > >
> >
> > ** Biggest safety myth out.
> >
> > Using an isolation transformer unnecessarily INCREASES electric shock risk.
>
> The UK government certainly disagrees with you.
>

** More arrogant bullshit.



We have used isolation transformers for decades in bathrooms ....


** FFS you congenital context shifimg **bullshitter **

- the TOPIC here is electronics servicing with an Iso in the AC supply!!!!!!


Go away, stay there.


.... Phil

[John-Del]

> .... Phil



Jeebus Phil you were doing so well recently.

[Phil Allison]

tabb...@gmail.com wrote:


> >
> > There are unique conditions in which an isolation transformer
> > does not prevent the risk of electric shock.
> > Therefore they increase the risk of electric shock.
> >

** What I wrote was that if the use of an iso tranny is not essential, you are better off not using one and taking all the usual precautions instead.

This detailed article by Rod Elliot explains why using an iso is hazardous - not that reading it will have the slightest impact on wooden heads like you or NT.

http://sound.whsites.net/articles/iso-xfmr.htm

FYI:

The use of an RCD, ELCB or other earth leakage detector ( aka safety switch) on a workbench is a safety essential.


.... Phil

[tabb...@gmail.com]

On Thursday, 8 November 2018 23:51:21 UTC, Phil Allison wrote:

> tabby wrote:
> > Phil Allison wrote:
> > >
>
> > > >
> > > > Well, they were standard & widespread in the 1990s.
> > >
> > > ** Live chassis tube TVs and radios " standard & widespread " in the 1990s ????
> >
> > Live chassis TVs were very common in the 90s.
>
>
> ** But not TUBE sets as the above requires.

Pretty much ALL TVs were CRT in the 90s.

> I have a 1990s 12 inch GE color portable where the whole chassis is live and only isolated by the antenna balun.
>
>
> > > FYI:
> > >
> > > The OP did NIT even mention "live chassis" so his post was wrong and so is yours.
> >
> > I was responding to your mention of 'hot chassis' not the OP's.
> > What the OP mentioned is irrelevant.
> >
>
> ** Bullshit. I was responding to the OP post - so what he wrote is totally relevant.

get a grip

> > > > > Contemporary use of 1:1 isolation transformers would be for
> > > > > servicing devices like SMPSs.
> > > > >
> > > > >
> > > > > > It removes the direct path to ground of the electrical power,
> > > > > > significantly reducing the chance of death.
> > > > >
> > > > > ** That is wrong.
> > > > >
> > > > > Using an isolation transformer allows one to connect the common
> > > > > rail ( or any other point) of an off-line SMPS to safety ground.
> > > > > After which you can use a scope in the normal way to investigate
> > > > > various waveforms, maybe small ones like MOSFET drive signals.
> > > >
> > > >
> > > > One can, but they are also used to reduce shock risk.
> > > >
> > >
> > > ** Biggest safety myth out.
> > >
> > > Using an isolation transformer unnecessarily INCREASES electric shock risk.
> >
> > The UK government certainly disagrees with you.
>
> ** More arrogant bullshit.

it's why they're mandated in bathrooms

> We have used isolation transformers for decades in bathrooms ....
>
> ** FFS you congenital context shifimg **bullshitter **
>
> - the TOPIC here is electronics servicing with an Iso in the AC supply!!!!!!

the principle is the exact same, namely that after an iso one would need to touch 2 parts of a circuit to get a shock not just 1.


NT

[tabb...@gmail.com]

On Friday, 9 November 2018 00:08:03 UTC, Phil Allison wrote:

> tabby wrote:
>
>
> > >
> > > There are unique conditions in which an isolation transformer
> > > does not prevent the risk of electric shock.
> > > Therefore they increase the risk of electric shock.
>
> ** What I wrote was that if the use of an iso tranny is not essential, you are better off not using one and taking all the usual precautions instead.
>
> This detailed article by Rod Elliot explains why using an iso is hazardous - not that reading it will have the slightest impact on wooden heads like you or NT.
>
> http://sound.whsites.net/articles/iso-xfmr.htm

an article with a lot of errors & dubious assumptions, as a result of which he comes to wrong conclusions. If I get the time I'll go through it.

> FYI:
>
> The use of an RCD, ELCB or other earth leakage detector ( aka safety switch) on a workbench is a safety essential.

I fixed lots of TVs with no such 'essential'. Most were live chassis. Any sensible person would advise using one now, but essential? We just used what was available & affordable at the time.


NT

[Phil Allison]

tabb...@gmail.com wrote:

> Phil Allison wrote:
> > tabby wrote:
> >
> >
> > > >
> > > > There are unique conditions in which an isolation transformer
> > > > does not prevent the risk of electric shock.
> > > > Therefore they increase the risk of electric shock.
> >
> > ** What I wrote was that if the use of an iso tranny is not essential,
> > you are better off not using one and taking all the usual precautions
> > instead.
> >
> > This detailed article by Rod Elliot explains why using an iso is
> > hazardous - not that reading it will have the slightest impact
> > on wooden heads like you or NT.
> >
> > http://sound.whsites.net/articles/iso-xfmr.htm
>
>
> an article with a lot of errors & dubious assumptions,

** All your posts are like that - but not the above.

> If I get the time I'll go through it.

** The context shifting bullshitter has not even read it.

Yawwwnnnn.......

>
> > FYI:
> >
> > The use of an RCD, ELCB or other earth leakage detector ( aka safety
> > switch) on a workbench is a safety essential.
>
>
>I fixed lots of TVs with no such 'essential'. Most were live chassis.
> Any sensible person would advise using one now, but essential?
>

** Try learning to read sometime - the phrase was "safety essential."

Obviously your life is not worth much.


..... Phil

[tabb...@gmail.com]

On Friday, 9 November 2018 06:10:01 UTC, Phil Allison wrote:
> tabby wrote:

> > Phil Allison wrote:

> > > This detailed article by Rod Elliot explains why using an iso is
> > > hazardous - not that reading it will have the slightest impact
> > > on wooden heads like you or NT.
> > >
> > > http://sound.whsites.net/articles/iso-xfmr.htm
> >
> >
> > an article with a lot of errors & dubious assumptions,
>
>
> ** All your posts are like that - but not the above.
>
>
> > If I get the time I'll go through it.
>
>
>
> ** The context shifting bullshitter has not even read it.
>
> Yawwwnnnn.......

ok, I won't waste my time on you.

[three_jeeps]

I think the point in this thread is that one has to know what they are dealing with before employing an isolation transformer. I read the article. IMO, the article title is an attention getting and his point is that the isolation transformer presents a 'false sense of safety'. The assumption that most ppl will make is that one blindly needs to install an isolation xformer in all applications and it will keep you safe. There are limitations based on the circuits one is dealing with.
The assertion to be safe one must "use of an RCD, ELCB or other earth leakage detector" is a general statement but also a bit misleading. RCDs are NOT recommended and ELCBs are essential. This article explains things quite well..
https://www.linkedin.com/pulse/what-difference-between-mcb-mccb-elcb-rccb-elcab-engineers

The statement about live chassis 'only in TV of the 90's' is grossly incorrect.
My father owned/operated a TV/Radio sales and service shop from early 50 through 2000. I grew up in the shop and serviced TVs and other electronic gear from the 60, 70, and 80s. I can attest that the live chassis was not only in the 90's. I've seen it in the 70s and 80's TVs. I've also seen it in electronic gear in the 2010s - e.g. soldering stations/hot air rework stations from China, as well as three voltage power supplies from China.
Point is, one needs to be aware of the realities of the circuitry they are working on and dont blindly apply 'safety measures'...that doesn't mean to ignore them. It means to apply them but know what areas of 'safety' they are meant to protect.

[tabb...@gmail.com]

On Friday, 9 November 2018 17:43:53 UTC, three_jeeps wrote:


> I think the point in this thread is that one has to know what they are dealing with before employing an isolation transformer. I read the article. IMO, the article title is an attention getting and his point is that the isolation transformer presents a 'false sense of safety'. The assumption that most ppl will make is that one blindly needs to install an isolation xformer in all applications and it will keep you safe. There are limitations based on the circuits one is dealing with.

To remain safe when working on live equipment one needs to understand what one is dealing with whatever safety systems are in use. Isos have their limitations of course, so do all safety methods.

> The assertion to be safe one must "use of an RCD, ELCB or other earth leakage detector" is a general statement but also a bit misleading. RCDs are NOT recommended and ELCBs are essential.

Woah. Voltage operated ELCBs are obsolete, a known hazard and offer no protection whatever against shock when working on a live chassis appliance. They only protect against the earth system becoming live as a result of a high current fault (not via a human) that would otherwise raise the earth system above 50v. That's all they do. They were obsolete in the 1980s. Current operated ELCBs _are_ RCDs.

> This article explains things quite well..
> https://www.linkedin.com/pulse/what-difference-between-mcb-mccb-elcb-rccb-elcab-engineers

It's yet another article with both correct points and some confusion.

> The statement about live chassis 'only in TV of the 90's' is grossly incorrect.
> My father owned/operated a TV/Radio sales and service shop from early 50 through 2000. I grew up in the shop and serviced TVs and other electronic gear from the 60, 70, and 80s. I can attest that the live chassis was not only in the 90's. I've seen it in the 70s and 80's TVs. I've also seen it in electronic gear in the 2010s - e.g. soldering stations/hot air rework stations from China, as well as three voltage power supplies from China.

Unless I'm mistaken I don't think anyone said live chassis kit only existed from the 90s. I have had live chassis stuff from post-2000, 90s, 80s, 70s, 60s, 50s, 40s, 30s, 20s and one item that might have been from the 10s or 20s. By the time you go that far back 'live chassis' becomes somewhat meaningless in that it was normal to have live bits all hanging out.

> Point is, one needs to be aware of the realities of the circuitry they are working on and dont blindly apply 'safety measures'...that doesn't mean to ignore them. It means to apply them but know what areas of 'safety' they are meant to protect.

that of course is vital when working on live equipment. Anyone that does so without understanding what they're doing or gets careless is in trouble. In about of 99.2% of those cases a shock awakes them to the need to be sensible. Mortality is somewhere roughly in the region of 1 per 600 shocks.

There is NO safety system that can protect people against that. RCDs offer zero protection against shock from transformer derived B+, don't protect against L-N shocks and don't always work on L-E shocks. ELCBs offer no shock protection at all from live working hazards. Isos offer limited protection. Never touching the equipment with both hands offers limited protection. An earth-free workzone offers limited protection, etc etc. Sometimes you just need to know what you're doing or not do it.


NT

[Phil Allison]

three_jeeps wrote:

>
> > ** What I wrote was that if the use of an iso tranny is not essential,
> > you are better off not using one and taking all the usual precautions
> > instead.
> >
> > This detailed article by Rod Elliot explains why using an iso is
> > hazardous - not that reading it will have the slightest impact on
> > wooden heads like you or NT.
> >
> > http://sound.whsites.net/articles/iso-xfmr.htm
> >
> > FYI:
> >
> > The use of an RCD, ELCB or other earth leakage detector
> ( aka safety switch) on a workbench is a safety essential.
> >
>
>

> I think the point in this thread is that one has to know what they are dealing with before employing an isolation transformer.

** Which practically counts out the servicing equipment with unknown faults.



> I read the article.


** Good for you.

IMO, the article title is an attention getting and his point is that the isolation transformer presents a 'false sense of safety'. The assumption that most ppl will make is that one blindly needs to install an isolation xformer in all applications and it will keep you safe. There are limitations based on the circuits one is dealing with.

> The assertion to be safe one must "use of an RCD, ELCB or other earth leakage detector" is a general statement but also a bit misleading. RCDs are NOT recommended and ELCBs are essential.

** The use of RCDs is highly recommended in the article *YOU* cited !!!!

QUOTE:

" RCDs are an extremely effective form of shock protection "
------------------------------------------------------------

> https://www.linkedin.com/pulse/what-difference-between-mcb-mccb-elcb-rccb-elcab-engineers

>
> The statement about live chassis 'only in TV of the 90's' is grossly
> incorrect.

** Good - cos no-one here actually said that.

Do you have a reading disability ??

Never mind, NG postings are notorious for being confusing & difficult to follow.



.... Phil

[Lucifer]

On Thu, 8 Nov 2018 19:09:09 -0800 (PST), tabb...@gmail.com wrote:

>On Friday, 9 November 2018 00:08:03 UTC, Phil Allison wrote:
>> tabby wrote:
>>
>>
>> > >
>> > > There are unique conditions in which an isolation transformer
>> > > does not prevent the risk of electric shock.
>> > > Therefore they increase the risk of electric shock.
>>
>> ** What I wrote was that if the use of an iso tranny is not essential,
>>you are better off not using one and taking all the usual precautions instead.
>>
>> This detailed article by Rod Elliot explains why using an iso is hazardous -
>> not that reading it will have the slightest impact on wooden heads like you
>> or NT.
>>
>> http://sound.whsites.net/articles/iso-xfmr.htm
>
>an article with a lot of errors & dubious assumptions, as a result of
>which he comes to wrong conclusions. If I get the time I'll go through
>it.

One error is where he writes,
"Without isolation, you know exactly what is dangerous at all times.
It's quite apparent that you can't touch anything that's at mains
potential,"

That's poor English. Obviously you can touch anything that's at
mains potential but you shouldn't.

[tabb...@gmail.com]

On Saturday, 24 November 2018 15:35:25 UTC, Lucifer wrote:

> On Thu, 8 Nov 2018 19:09:09 -0800 (PST), tabbypurr wrote:
> >On Friday, 9 November 2018 00:08:03 UTC, Phil Allison wrote:
> >> tabby wrote:

> >> This detailed article by Rod Elliot explains why using an iso is hazardous -
> >> not that reading it will have the slightest impact on wooden heads like you
> >> or NT.
> >>
> >> http://sound.whsites.net/articles/iso-xfmr.htm
> >
> >an article with a lot of errors & dubious assumptions, as a result of
> >which he comes to wrong conclusions. If I get the time I'll go through
> >it.
>
> One error is where he writes,
> "Without isolation, you know exactly what is dangerous at all times.
> It's quite apparent that you can't touch anything that's at mains
> potential,"
>
> That's poor English. Obviously you can touch anything that's at
> mains potential but you shouldn't.

one of too many errors in that article.


NT

[Phil Allison]

Lucifer wrote:

>
> >
> >> This detailed article by Rod Elliot explains why using an iso is hazardous

> >> not that reading it will have the slightest impact on wooden heads like you
> >> or NT.
> >>
> >> http://sound.whsites.net/articles/iso-xfmr.htm

>

> One error is where he writes,
>
> "Without isolation, you know exactly what is dangerous at all times.
> It's quite apparent that you can't touch anything that's at mains
> potential,"
>
> That's poor English.

** The English grammar is fine and there is no technical error.

> Obviously you can touch anything that's at mains potential but you shouldn't.

** Wot pedantic twaddle, the word "safely" in front of the word "touch" is understood from general context.


.... Phil

[peter wieck]

There are times when I am told: But, you know what I mean!

To which the only valid answer is: No, I know what you said (wrote). I am still trying to discern what you mean.

Be very, very careful about making assumptions in a technical discussion, and in using any of poor grammar, syntax, word-choice, punctuation or spelling. The consequences may be significant - and surprising.