Re: 'Earth' levels of TV cables.
Bazzer Smith
"Bazzer Smith" <m...@invalid.net> wrote in message
news:ARvDg.16760$vl5....@newsfe4-win.ntli.net...
>I sort of covered this in a earlier post but it might get 'buried'. If you
>connect two different TV RF cables togeather (via a coupler or whatever
>just directly) should
> there be a potential difference (voltage) between the two 'earths'? I ask
> because there seemed to be a 4-5 volt difference when I tried this, at
> least that's what I measured on my multi-meter, maybe I did it wrong?, I
> had it on AC but it 'felt' AC when it went through my fingers :O)
>
> By the way I have not done any DIY work on my houses electrical circuits,
> well not yet anyway ;O) I doubt I could make it any worse even if I did, I
> think the builders who built it wore spurs!!
>
> Maybe its a 'false' reading anyway because 5 volts through a path of
> minimal resistance would draw a big current which would probably burn the
> wiring out, or atleast
> explain my huge electricty bills!!
Forwarded to uk.d-i-y
>
>
Agamemnon
>
> "Bazzer Smith" <m...@invalid.net> wrote in message
> news:ARvDg.16760$vl5....@newsfe4-win.ntli.net...
>>I sort of covered this in a earlier post but it might get 'buried'. If you
>>connect two different TV RF cables togeather (via a coupler or whatever
>>just directly) should
>> there be a potential difference (voltage) between the two 'earths'? I ask
Are they both connected to the same earth terminal ?
Even if they are the earth screen will act as short wave antenna so will
pick up electromagnetic radiation and that's probably what your meter is
measuring if you set it on AC. Even if you hold the metal part of meters
prods one in each hand without anything else connected it will still give
you a reading.
>> because there seemed to be a 4-5 volt difference when I tried this, at
>> least that's what I measured on my multi-meter, maybe I did it wrong?, I
>> had it on AC but it 'felt' AC when it went through my fingers :O)
How can you feel 4 or 5 volts through your fingers. Were they wet ?
>>
>> By the way I have not done any DIY work on my houses electrical circuits,
>> well not yet anyway ;O) I doubt I could make it any worse even if I did,
>> I think the builders who built it wore spurs!!
>>
>> Maybe its a 'false' reading anyway because 5 volts through a path of
>> minimal resistance would draw a big current which would probably burn the
>> wiring out, or atleast
>> explain my huge electricty bills!!
Have you tried measuring the current ?
A volt meter has a very high internal resistance which is why it is able to
measure even very low voltages between two unconnected wires. Since the
resistance between them is huge very little current is flowing. If you use
an ammeter to measure the current it I doubt you would get any current
flowing at all.
>
>
> Forwarded to uk.d-i-y
>
>>
>>
>
>
gort
>>> because there seemed to be a 4-5 volt difference when I tried this, at
>>> least that's what I measured on my multi-meter, maybe I did it wrong?, I
>>> had it on AC but it 'felt' AC when it went through my fingers :O)
>
> How can you feel 4 or 5 volts through your fingers. Were they wet ?
This is ' Bazzer Smith ' don't forget !!!. Words, salt and pinch of,
spring to mind.
Dave
Prometheus
<agam...@hello.to.NO_SPAM> writes
>How can you feel 4 or 5 volts through your fingers. Were they wet ?
I can think of a mechanism. But its validity depends on the properties
of the multimeter the OP used to measure it.
--
Ian G8ILZ
Stephen
>
> "Bazzer Smith" <m...@invalid.net> wrote in message
> news:ARvDg.16760$vl5....@newsfe4-win.ntli.net...
> >I sort of covered this in a earlier post but it might get 'buried'. If
you
> >connect two different TV RF cables togeather (via a coupler or whatever
> >just directly) should
> > there be a potential difference (voltage) between the two 'earths'? I
ask
> > because there seemed to be a 4-5 volt difference when I tried this, at
> > least that's what I measured on my multi-meter, maybe I did it wrong?, I
> > had it on AC but it 'felt' AC when it went through my fingers :O)
If it registers 4 or 5 volts but you can feel it, it's probably mains
voltage, or half mains voltage connected to your fingers via the supression
capacitors across the mains inlet of one of the bits of equipment you are
using. There's a small capacitor between Live and Earth, and another equal
capacitor between Neutral and Earth. If one of your mains Earth connections
has been disconnected somewhere then the equipment's Earth cable, it's case
and any aerial sockets plugged into it, will be at half mains voltage but at
a very high impedance due to the capacitors.
If you put your voltmeter on a higher range you will probably see a higher
reading as the impedance of the meter will be higher. If you connect an
oscilloscope in the same place you will probably see over 100 volts at 50
Hz.
meow...@care2.com
If 2 cables are connected there isnt 4-5 volts between them. If the
cables are 4-5v from earth you wont feel anything. If theyre 4-5v from
each other and live you would. I've not come across multimeters reading
hf rf before; it would need to be very high freq not to be shorted out
by a short metallic connection. If you can sort out the facts maybe we
can help. Maybe crosspost to sci.electronics.basics.
NT
Prometheus
meow...@care2.com writes
>Bazzer Smith wrote:
>> "Bazzer Smith" <m...@invalid.net> wrote in message
>> news:ARvDg.16760$vl5....@newsfe4-win.ntli.net...
>
>> >I sort of covered this in a earlier post but it might get 'buried'. If you
>> >connect two different TV RF cables togeather (via a coupler or whatever
>> >just directly) should
>> > there be a potential difference (voltage) between the two 'earths'? I ask
>> > because there seemed to be a 4-5 volt difference when I tried this, at
>> > least that's what I measured on my multi-meter, maybe I did it wrong?, I
>> > had it on AC but it 'felt' AC when it went through my fingers :O)
>> >
>> > By the way I have not done any DIY work on my houses electrical circuits,
>> > well not yet anyway ;O) I doubt I could make it any worse even if I did, I
>> > think the builders who built it wore spurs!!
>> >
>> > Maybe its a 'false' reading anyway because 5 volts through a path of
>> > minimal resistance would draw a big current which would probably burn the
>> > wiring out, or atleast
>> > explain my huge electricty bills!!
>>
>>
>> Forwarded to uk.d-i-y
>
>
>If 2 cables are connected there isnt 4-5 volts between them.
Correct.
>If the
>cables are 4-5v from earth you wont feel anything.
Incorrect!
>If theyre 4-5v from
>each other and live you would. I've not come across multimeters reading
>hf rf before;
Who said it was RF?
Besides, have you any idea how much RF (how close and how powerful a TX)
you would need to measure 5V?
>it would need to be very high freq not to be shorted out
>by a short metallic connection.
It might be an inductive coupler with no galvanic coupling.
--
Ian G8ILZ
Bazzer Smith
"Agamemnon" <agam...@hello.to.NO_SPAM> wrote in message
news:asqdnYmIa93...@pipex.net...
>
> "Bazzer Smith" <m...@invalid.net> wrote in message
> news:tSvDg.16761$vl5....@newsfe4-win.ntli.net...
>>
>> "Bazzer Smith" <m...@invalid.net> wrote in message
>> news:ARvDg.16760$vl5....@newsfe4-win.ntli.net...
>>>I sort of covered this in a earlier post but it might get 'buried'. If
>>>you connect two different TV RF cables togeather (via a coupler or
>>>whatever just directly) should
>>> there be a potential difference (voltage) between the two 'earths'? I
>>> ask
>
> Are they both connected to the same earth terminal ?
To different power points in the same room. The Freeview dongle is connected
to
my PC via the USB, I don't know what that means about its earth.
>
> Even if they are the earth screen will act as short wave antenna so will
> pick up electromagnetic radiation and that's probably what your meter is
> measuring if you set it on AC. Even if you hold the metal part of meters
> prods one in each hand without anything else connected it will still give
> you a reading.
>
>>> because there seemed to be a 4-5 volt difference when I tried this, at
>>> least that's what I measured on my multi-meter, maybe I did it wrong?, I
>>> had it on AC but it 'felt' AC when it went through my fingers :O)
>
> How can you feel 4 or 5 volts through your fingers. Were they wet ?
They may have been after I washed my hands from being in the attic.
Andy Burns
> To different power points in the same room. The Freeview dongle is connected
> to
> my PC via the USB, I don't know what that means about its earth.
That means they are probably just connected to the PC's signal ground,
not to actual earth, especially if a laptop, also equipment could be
double insulated and have no earth ...
John Rumm
Yet another possibility is that the whole house has a high earth
impedance (e.g. as is quite common with a TT earthing system (local
earth rod) and an overhead cable power supply to the house).
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
The Natural Philosopher
> Andy Burns wrote:
>
>> Bazzer Smith wrote:
>>
>>> To different power points in the same room. The Freeview dongle is
>>> connected to
>>> my PC via the USB, I don't know what that means about its earth.
>>
>>
>> That means they are probably just connected to the PC's signal ground,
>> not to actual earth, especially if a laptop, also equipment could be
>> double insulated and have no earth ...
>
> Yet another possibility is that the whole house has a high earth
> impedance (e.g. as is quite common with a TT earthing system (local
> earth rod) and an overhead cable power supply to the house).
>
>
once that may be relevant.
One laptop. One PC, one serial cable being used (before the days of USB
etc) to transfer data between them.
One teeny spark, and blown serial ports on both..
One voltmeter of high impedance variety conncted between the PC earth
and the laptop ground shows 115v AC..
The cause? The laptop was powered via an RFI filter with a capacitor
from live and neutral to the laptop ground, with the SUPPLIED 2 WIRE
MAINS PLUG.
i.e. there was NO mains earth on the laptop whatsoever..and the RFI
filter bled enough current through the capacitors to cause enough of a
surge to blow some components.
meow...@care2.com
What scenario are you proposing? Leaning on a live appliance? Sticking
2 pins through the heart and applying 4-5v? Either is possible but I'd
say quite unlikely.
> >If theyre 4-5v from
> >each other and live you would. I've not come across multimeters reading
> >hf rf before;
>
> Who said it was RF?
I dont remember who, someone said it may be. Read up if you really want
to know
> Besides, have you any idea how much RF (how close and how powerful a TX)
> you would need to measure 5V?
this seems to answer it:
> >it would need to be very high freq not to be shorted out
> >by a short metallic connection.
> It might be an inductive coupler with no galvanic coupling.
Normally screens are connected in domestic aerial installs, but sure it
might be just about anything. You never know.
NT
John Rumm
> i.e. there was NO mains earth on the laptop whatsoever..and the RFI
> filter bled enough current through the capacitors to cause enough of a
> surge to blow some components.
Yup, had exactly that happen in an office once. We were using two PCs
eitehr side of the room, hooked up via a serial cable, and got a slight
kick from the shield of the cable on plugging it in - nett result dead
port on one PC.
The place was wired with singles in metal conduit, and used the conduit
as a CPC. It turned out that the gland on one of the the sockets
providing connection to the conduit had worked loose over the years.
Bazzer Smith
"John Rumm" <see.my.s...@nowhere.null> wrote in message
news:44df899c$0$18504$ed2e...@ptn-nntp-reader04.plus.net...
> Andy Burns wrote:
>
>> Bazzer Smith wrote:
>>
>>> To different power points in the same room. The Freeview dongle is
>>> connected to
>>> my PC via the USB, I don't know what that means about its earth.
>>
>>
>> That means they are probably just connected to the PC's signal ground,
>> not to actual earth, especially if a laptop, also equipment could be
>> double insulated and have no earth ...
>
> Yet another possibility is that the whole house has a high earth impedance
> (e.g. as is quite common with a TT earthing system (local earth rod) and
> an overhead cable power supply to the house).
>
should share the same earth, however, one unit is a set top box
with its own power supply, so it only has two cables going to it,
live and 'earth', dunno which of the two earths it uses (earth or neutral)
same would go for the freeview dongle.
Anyway I tried measuring amps and it read nothing, volts gave 87V on
AC!! So I aint to sure what is going on, all I know is that my signal
booster
is dead.
I would also add that I detected a spark when plugging the aerial in to the
TV directly on one occasion!! TV is OK but it was rather disconcerting!!
It was audible and visable, the sort of thing which would easilly blow a
transistor
designed for small signals as in TV signals.
John Rumm
> "John Rumm" <see.my.s...@nowhere.null> wrote in message
>>Yet another possibility is that the whole house has a high earth impedance
> anyway both units are in the same room so they
> should share the same earth,
That could be the same *bad* earth.
> however, one unit is a set top box
> with its own power supply, so it only has two cables going to it,
> live and 'earth', dunno which of the two earths it uses (earth or neutral)
> same would go for the freeview dongle.
> Anyway I tried measuring amps and it read nothing, volts gave 87V on
> AC!! So I aint to sure what is going on, all I know is that my signal
Sounds like capacitive coupling caused by the input filter on the PSU.
You ought to be reading about half mains voltage if that were the case.
Graham
I was called out to investigate problems at one newly refurbished and
enlarged shop.
All the monitors displayed severe hum-bars and there was a defining hum on
the
PA system.
The satellite receiver and C-MAC decoder were located on a wallboard on one
side of the building and the monitors, text computer video distribution amp
and audio amplifier on the other.
The shop had been two separate units, (you guys are ahead of me now yes)?
The installation was using two different supply phases.
--
Graham.
%Profound_observation%
Christian McArdle
you
>> connect two different TV RF cables togeather (via a coupler or whatever
>> just directly) should there be a potential difference (voltage) between
>> the two 'earths'?
Basically yes. If you have two imperfectly earthed aerial cables, there is
likely to be considerable potential difference between the two earths.
Indeed, you often get quite a little belt by touching the two earths before
the cables are mated. Often the "earth" never gets earthed at all, because
the TV is double insulated and the aerial not earthed.
Christian.
Graham
>
>
> The satellite receiver and C-MAC decoder were located on a wallboard on
Just remembered that SIS used B-MAC not C-MAC.
Also intended that to follow-on a different part of this thread. Never mind.
--
Graham.
%Profound_observation%
Guy King
from "Graham" <m...@privacy.com> contains these words:
> c. 1990 I was involved with commissioning SIS systems in betting shops.
For Rediffusion/Ladbrokes? I did dozens of them all over the Home
Counties, but a few years before that - some time around mid 80s.
Getting those 26" tellies into the racks was a bastard.
--
Skipweasel
Pay no attention to that man behind the curtain.
Graham
>
>> c. 1990 I was involved with commissioning SIS systems in betting shops.
>
> For Rediffusion/Ladbrokes? I did dozens of them all over the Home
> Counties, but a few years before that - some time around mid 80s.
> Getting those 26" tellies into the racks was a bastard.
No, later than that, at the time when Extel gave way to SIS.
BT installed the satellite kit, someone else installed the cabling and we,
Granada,
did the rest.
GTVR (I think they were called UKRS then) installed the TV's and
I turned up in my Granada Microcare blazer and installed the computer,
connected the whole
thing up and commissioned it.
--
Graham.
%Profound_observation%
Bazzer Smith
"Guy King" <guy....@zetnet.co.uk> wrote in message
news:3130303034323...@zetnet.co.uk...
> The message <44e0596e$1...@x-privat.org>
> from "Graham" <m...@privacy.com> contains these words:
>
>> c. 1990 I was involved with commissioning SIS systems in betting shops.
>
> For Rediffusion/Ladbrokes? I did dozens of them all over the Home
> Counties, but a few years before that - some time around mid 80s.
> Getting those 26" tellies into the racks was a bastard.
I would imagine its a tad easier these days, they must be using flat panel
monitors in new shops.
Graham
>
> I would imagine its a tad easier these days, they must be using flat panel
> monitors in new shops.
Have you ever tried lifting a PDP?
--
Graham.
%Profound_observation%
meow...@care2.com
> > I would imagine its a tad easier these days, they must be using flat panel
> > monitors in new shops.
> Have you ever tried lifting a PDP?
reckon you'd put that down PDQ
NT
Graham
"Huge" <Hu...@nowhere.much.invalid> wrote in message
news:ecs95c$44p$1...@apophis.demon.co.uk...
> On 2006-08-27, Graham <m...@privacy.com> wrote:
>>
>>>
>>> I would imagine its a tad easier these days, they must be using flat
>>> panel
>>> monitors in new shops.
>>
>> Have you ever tried lifting a PDP?
>
> into the Bletchley Park Computer Museum the weekend before last. It
> was only a 2U 19" rackmount. No disks, mind.
Doesn't the floating point option make it lighter?
--
Graham.
%Profound_observation%
Dave Liquorice
> Doesn't the floating point option make it lighter?
Only up to a point.
--
Cheers new...@howhill.com
Dave. pam is missing e-mail