Volt Appearing Between White Neutral And Gnd Wire ?

[Robert11]

Hello:

Have been trying to get some smoke detectors interconnected, and
during the trouble shooting of the problem, I measured (with an analog
voltmeter) the
voltage between the white neutral, and the bare copper ground wire in the
box.

Was very surprised to see that it was about 2 V AC.

Other than the fairly obvious reasons, such as bad ground connections in the
service box for the neutral or gnd, or within the wiring chain itself, was
wondering if anyone might have any other thoughts or opinions on this.

Might as well add this: The smoke detectors were on line, and functioning,
when I measured.
The interconnect for the smoke detectors (the third, red, wire ) uses the
white neutral (also)
as it's return. And, measuring a few outlets around the house showed 0
voltage between the neutral and gnd as one would expect.

But, even if the smokes were dumping something on the white neutral, it
being at gnd potential, would "sink" these voltages immediately, I would
think, if the neutral was grounded well.
So, what might be happening ?

BTW: How "common" is it to see voltages of this magnitude between the white
neutral and ground ?

Thanks,
B.

 

[Roger Hamlett]

"Robert11" <rgsrose@notme.com> wrote in message
news:HsudnXDa-MRpMfLfRVn-vA@comcast.com...

Hello:

Have been trying to get some smoke detectors interconnected, and
during the trouble shooting of the problem, I measured (with an analog
voltmeter) the
voltage between the white neutral, and the bare copper ground wire in
the box.

Was very surprised to see that it was about 2 V AC.

Other than the fairly obvious reasons, such as bad ground connections in
the service box for the neutral or gnd, or within the wiring chain
itself, was wondering if anyone might have any other thoughts or
opinions on this.

Might as well add this: The smoke detectors were on line, and
functioning, when I measured.
The interconnect for the smoke detectors (the third, red, wire ) uses
the white neutral (also)
as it's return. And, measuring a few outlets around the house showed 0
voltage between the neutral and gnd as one would expect.

But, even if the smokes were dumping something on the white neutral, it
being at gnd potential, would "sink" these voltages immediately, I would
think, if the neutral was grounded well.
So, what might be happening ?

BTW: How "common" is it to see voltages of this magnitude between the
white neutral and ground ?

Thanks,
B.
Very normal.

The earth wire, and neutral, are joined nominally at one point. When power
is drawn between live and neutral in the system, the resistance between
the point where the power is drawn, and the connection, will result
voltage being present, between the neutral and the ground, if measured
anywhere but at the connection point.

Best Wishes

 

[John Woodgate]

I read in sci.electronics.design that Robert11 <rgsrose@notme.com> wrote
(in <HsudnXDa-MRpMfLfRVn-vA@comcast.com&gt about 'Volt Appearing Between
White Neutral And Gnd Wire ?', on Wed, 27 Apr 2005:

But, even if the smokes were dumping something on the white neutral, it
being at gnd potential, would "sink" these voltages immediately, I
would
think, if the neutral was grounded well.

No. The neutral wire is not a superconductor, and it carries currents.

Even 'ground potential' can mean different things in different places.
There OUGHT not to be any current in the ground conductor, unlike the
neutral, so its potential SHOULD be the same everywhere, but there
always are leakage currents, so even the 'ground' ground isn't perfect.

So, what might be happening ?

ANY piece of wire has resistance. This applies to neutral wires and
ground wires. What you are seeing, from your description, is the voltage
dropped across the resistance of the neutral wire due to the current
flowing in it. Where that current is coming from is not determinable by
what you have told us

BTW: How "common" is it to see voltages of this magnitude between the
white
neutral and ground ?

It is a bit high, but....
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[SioL]

"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message news:i8Obe.582$iQ1.466@newsfe4-gui.ntli.net...

BTW: How "common" is it to see voltages of this magnitude between the white neutral and ground ?

Thanks,
B.
Very normal.
The earth wire, and neutral, are joined nominally at one point. When power is drawn between live and neutral in the system, the
resistance between the point where the power is drawn, and the connection, will result voltage being present, between the neutral
and the ground, if measured anywhere but at the connection point.

Best Wishes

With other words, if you disconnect all the mains powered devices in your
house (especially the heavy loads, such as a stowe) this voltage falls down to 0V.

--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."

 

[Mike Monett]

Ken Smith wrote:

[...]

I saw about 10mV in the one case where I measured. That was on a house
built before the "bonded" grounding was required. The "green" wire was
actually a bare wire that ran back to the water pipe.

kensmith@rahul.net forging knowledge

The house I stayed in Ottawa also connected the "green" wire to the water
pipe.

The house was supplied by a well. Two inches from the ground connection,
the copper pipe connected to a plastic pipe that ran though the concrete
to the outside well.

So all the grounds were connected together, but they didn't connect to
anything!

It passed inspection by the building inspector. Rules said the ground had
to connect to the water pipe. It did.

Mike Monett

 

[Ken Smith]

In article <X%Obe.11779$F6.2362214@news.siol.net>,
SioL <Sio_spam_L@same.net> wrote:
[...]

With other words, if you disconnect all the mains powered devices in your
house (especially the heavy loads, such as a stowe) this voltage falls
down to 0V.

(USA location specific)

Depending of the house etc, you may also have to shut off the power next
door to get it really down to zero. In some places there are two
connections to earth the ground, one for the white and one for the green.
This is done so that ground return current in the white can't raise the
voltage on the green. A small AC voltage can still be seen even with the
main breaker to the house pulled.

I saw about 10mV in the one case where I measured. That was on a house
built before the "bonded" grounding was required. The "green" wire was
actually a bare wire that ran back to the water pipe.






--
--
kensmith@rahul.net forging knowledge

 

[John Crighton]

On Wed, 27 Apr 2005 17:05:46 +0100, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Robert11 <rgsrose@notme.com> wrote
(in <HsudnXDa-MRpMfLfRVn-vA@comcast.com&gt about 'Volt Appearing Between
White Neutral And Gnd Wire ?', on Wed, 27 Apr 2005:

But, even if the smokes were dumping something on the white neutral, it
being at gnd potential, would "sink" these voltages immediately, I
would
think, if the neutral was grounded well.

No. The neutral wire is not a superconductor, and it carries currents.

Even 'ground potential' can mean different things in different places.
There OUGHT not to be any current in the ground conductor, unlike the
neutral, so its potential SHOULD be the same everywhere, but there
always are leakage currents, so even the 'ground' ground isn't perfect.

So, what might be happening ?

ANY piece of wire has resistance. This applies to neutral wires and
ground wires. What you are seeing, from your description, is the voltage
dropped across the resistance of the neutral wire due to the current
flowing in it. Where that current is coming from is not determinable by
what you have told us

BTW: How "common" is it to see voltages of this magnitude between the
white
neutral and ground ?

It is a bit high, but....
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Hello Gents,
reading this thread brought back memories of a bad
experience when I was an apprentice in the late 1960s.

I was doing a few months experience in a cal lab and
was working on an old chart recorder. The 240 volt
input connector was a Bulgin type. Old fashioned now.

I was fascinated by this 3 or 4 volts appearing between
earth and neutral as it seemed like a source of free
power. I had heard stories of one fellow running low
voltage globes permanently in his outside brick toilet.
Energy for free!

Here was the Active Neutral and Earth exposed in front
of me inside this chart recorder so I thought I would
make a few measurements.

I was using a couple of AVO model 8 multimeters to
poke around the rear of this small mains input connector
of the chart recorder. The old AVO meter test prods were
massive by to-days standards. One meter was measuring
the volts between Neutral and Earth, about 3 or 4.

I used resistors as loads and the second AVO meter
to measure current. The voltage dropped readily.
I reduced the load resistor to near zero ohms by shorting
out the the neutral to earth via the second AVO meter.
I noted that the meter reading was roughly 2 amps.
The voltage between Neutral and Earth dropped
to zero as expected.
Then Flash Bang! The work shop was in darkness!
The large meter prods slipped off the back of the
Bulgin mains connector. One meter prod was melted.

"No problem," said the boss. "just reset the circuit
beaker on the power box outside." I had never
seen a circuit breaker before but I saw that one of
lever switches was not in the same position as the
rest so I tried moving it. I tried several times to
move it in to position and it just kept buzzing and
returning to the off position.

I returned to the workshop to tell my fellow
workers that the circuit breaker will not stay
in position only to find them staring at a very
blackened chart recorder then glaring at me.
The chart recorder had been emitting smoke
and sparks each time I was attempting to reset
the circuit breaker.
I hadn't unplugged the chart recorder when I was
told to reset the circuit breaker outside the building.
Boy did I cop it from the boss!
I didn't tell the boss what I was really doing,
"just measuring the mains supply according to
procedures in the book and my meter prod slipped."
I don't think he believed me.

I worked my arse off cleaning up the insides
of that chart recorder. Some of the black shit
would not come off resistors and capacitors so
I ran around trying to find replacements.

I learned about "carbon tracking" that was
caused between the pins of the Bulgin mains
connector when the multimeter prod fell across
the pins and shorted the 240V supply.
I learned what a circuit breaker was.
I learned not to mess with customers gear.
I learned a lot that day!
Never to be forgotten!

Regards
John Crighton
Sydney

 

[SioL]

"Mike Monett" <no@spam.com> wrote in message news:42705EA9.3140@spam.com...

The house I stayed in Ottawa also connected the "green" wire to the water
pipe.

The house was supplied by a well. Two inches from the ground connection,
the copper pipe connected to a plastic pipe that ran though the concrete
to the outside well.

So all the grounds were connected together, but they didn't connect to
anything!

It passed inspection by the building inspector. Rules said the ground had
to connect to the water pipe. It did.

Mike Monett

Taking a shower could be fun in such a house


--
Siol
------------------------------------------------
Rather than a heartless beep
Or a rude error message,
See these simple words: "File not found."

 

[Pat Ford]

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:d4qph1$2n5$1@blue.rahul.net...

In article <42705EA9.3140@spam.com>, Mike Monett <no@spam.com> wrote:
Ken Smith wrote:

[...]

I saw about 10mV in the one case where I measured. That was on a house
built before the "bonded" grounding was required. The "green" wire was
actually a bare wire that ran back to the water pipe.

kensmith@rahul.net forging knowledge

The house I stayed in Ottawa also connected the "green" wire to the water
pipe.

The house was supplied by a well. Two inches from the ground connection,
the copper pipe connected to a plastic pipe that ran though the concrete
to the outside well.

So all the grounds were connected together, but they didn't connect to
anything!

It passed inspection by the building inspector. Rules said the ground had
to connect to the water pipe. It did.

It actually would be safe unless you watered the garden. The water pipes
would be the only return path you could touch inside the house.

Everything could be at 1000V so long as nothing you can touch is at zero.

The water in the garden hose could be at 120V and, on some hot day, you
decide to run through the sprinkler in bare feet.

--
--
kensmith@rahul.net forging knowledge

The inspector was wrong the NEC clearing states that in that case there HAS
to be a ground wire. I'm just going through some of that stuff now, in the
book it is recommended that the wire be the same gauge as the wires for L1
and L2 combined but it also says in most case the wire just has to have the
same current carrying cap as either L1 or L2.
Pat

 

[Ken Smith]

In article <42705EA9.3140@spam.com>, Mike Monett <no@spam.com> wrote:

Ken Smith wrote:

[...]

I saw about 10mV in the one case where I measured. That was on a house
built before the "bonded" grounding was required. The "green" wire was
actually a bare wire that ran back to the water pipe.

kensmith@rahul.net forging knowledge

The house I stayed in Ottawa also connected the "green" wire to the water
pipe.

The house was supplied by a well. Two inches from the ground connection,
the copper pipe connected to a plastic pipe that ran though the concrete
to the outside well.

So all the grounds were connected together, but they didn't connect to
anything!

It passed inspection by the building inspector. Rules said the ground had
to connect to the water pipe. It did.

It actually would be safe unless you watered the garden. The water pipes
would be the only return path you could touch inside the house.

Everything could be at 1000V so long as nothing you can touch is at zero.

The water in the garden hose could be at 120V and, on some hot day, you
decide to run through the sprinkler in bare feet.

--
--
kensmith@rahul.net forging knowledge

 

[Ken Smith]

In article <d4qpqn$fkp$1@nrc-news.nrc.ca>, Pat Ford <pat.ford@nrcdotca> wrote:
[...]

The inspector was wrong the NEC clearing states that in that case there HAS
to be a ground wire. I'm just going through some of that stuff now, in the
book it is recommended that the wire be the same gauge as the wires for L1
and L2 combined but it also says in most case the wire just has to have the
same current carrying cap as either L1 or L2.
Pat

I assume that is the current standard. It is not unreasonable to assume
that at an earlier date, it did not contain that text. Back when plastic
pipe had never been heard of, it would be natural for them to assume a
metal pipe. At one time, "knob and tube" wiring was the standard.

--
--
kensmith@rahul.net forging knowledge

 

[Pat Ford]

"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:d4qq3n$2n5$3@blue.rahul.net...

In article <d4qpqn$fkp$1@nrc-news.nrc.ca>, Pat Ford <pat.ford@nrcdotca
wrote:
[...]
The inspector was wrong the NEC clearing states that in that case there
HAS
to be a ground wire. I'm just going through some of that stuff now, in
the
book it is recommended that the wire be the same gauge as the wires for
L1
and L2 combined but it also says in most case the wire just has to have
the
same current carrying cap as either L1 or L2.
Pat

I assume that is the current standard. It is not unreasonable to assume
that at an earlier date, it did not contain that text. Back when plastic
pipe had never been heard of, it would be natural for them to assume a
metal pipe. At one time, "knob and tube" wiring was the standard.

--
--
kensmith@rahul.net forging knowledge

The house I'm moving into this weekend has some knob and tube wirring, that
stuff is scarey!
PAt

 

[Guy Macon]

Ken Smith wrote:

In article <d4qpqn$fkp$1@nrc-news.nrc.ca>, Pat Ford <pat.ford@nrcdotca
wrote: [...]

The inspector was wrong the NEC clearing states that in that case there HAS
to be a ground wire. I'm just going through some of that stuff now, in the
book it is recommended that the wire be the same gauge as the wires for L1
and L2 combined but it also says in most case the wire just has to have the
same current carrying cap as either L1 or L2.
Pat

I assume that is the current standard. It is not unreasonable to assume
that at an earlier date, it did not contain that text. Back when plastic
pipe had never been heard of, it would be natural for them to assume a
metal pipe. At one time, "knob and tube" wiring was the standard.

An electrical inspector is required to inspect to the current NEC,
not an obsolete one.

 

[John Woodgate]

I read in sci.electronics.design that Guy Macon
<_see.web.page_@_www.guymacon.com_> wrote (in
<1171uoptnhrede@corp.supernews.com&gt about 'Volt Appearing Between White
Neutral And Gnd Wire ?', on Thu, 28 Apr 2005:

An electrical inspector is required to inspect to the current NEC, not
an obsolete one.

But what if the inspector is of similar vintage to the obsolete
standard? (;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk