Neutral/ground issue


T

Tuyen

I have a problem outlet that reads 30V (digital voltmeter) between
neutral and ground, 88V between hot and neutral and 120V between hot
and ground. The outlet is on a branch circuit; it appears to be the
only outlet on the branch. Other branches of the circuit show the
normal 120V between hot and neutral. I shut off all the breakers at the
panel except the breaker for the problem outlet. The voltage readings
do not change. I then shut off the breaker for the problem outlet (all
breakers now off) and the outlet now shows zero voltage between all
wires. The voltages at the panel appear normal. Also: there is no
continuity between ground and neutral at the problem outlet. This would
suggest an open neutral, but what would cause the voltage differentials
on the neutral wire if it was open? There isn't an obvious back load
soure such as an appliance.

I'm going to attempt to find out where the branch ties in, but it's a
1950's split level with pretty inaccessible wiring. I hate older
houses... help!

-T
 
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S

Sev

This actually sounds strange, since if there is a leak from hot to
neutral, it ought to feed back to other neutral wires which are tied in
to it. But perhaps not, if they are not really making good contact,
just close enough to leak a little current. Did you replace receptacle
itself/ retest? After that, I'd say you have to trace branch. Can you
see the most logical route for it to join rest of circuit? If not, you
may just have to identify all devices on circuit, then by trial and
error disconnect wires at one at a time, recap wires and turn power
back on till you find where branch is fed from. Look for poor
insulation, broken or defective devices. If still no luck, may be
wiring itself- as you say, it's from 50's.
Anyway, keep reading here- others may tell you how to find this more
easily with meter- not my forte.
 
L

lee houston

Tuyen said:
I have a problem outlet that reads 30V (digital voltmeter) between
neutral and ground, 88V between hot and neutral and 120V between hot
and ground.
have you opened the outlet and made sure it's wired correctly? i.e., the
ground and neutral are not swapped? ground on outlet is green or
bare?


The outlet is on a branch circuit; it appears to be the
 
M

Mark Lloyd

I have a problem outlet that reads 30V (digital voltmeter) between
neutral and ground, 88V between hot and neutral and 120V between hot
and ground. The outlet is on a branch circuit; it appears to be the
only outlet on the branch. Other branches of the circuit show the
normal 120V between hot and neutral. I shut off all the breakers at the
panel except the breaker for the problem outlet. The voltage readings
do not change. I then shut off the breaker for the problem outlet (all
breakers now off) and the outlet now shows zero voltage between all
wires. The voltages at the panel appear normal. Also: there is no
continuity between ground and neutral at the problem outlet. This would
suggest an open neutral, but what would cause the voltage differentials
on the neutral wire if it was open? There isn't an obvious back load
soure such as an appliance.
Open neutral. Induced voltage.
I'm going to attempt to find out where the branch ties in, but it's a
1950's split level with pretty inaccessible wiring. I hate older
houses... help!

-T
--
Mark Lloyd
http://notstupid.laughingsquid.com

"Democracy is two wolves and a lamb voting on what
to have for lunch. Liberty is a well armed lamb
contesting the vote." - Benjamin Franklin
 
T

ToMh

Tuyen said:
I have a problem outlet that reads 30V (digital voltmeter) between
neutral and ground, 88V between hot and neutral and 120V between hot
and ground. The outlet is on a branch circuit; it appears to be the
only outlet on the branch. Other branches of the circuit show the
normal 120V between hot and neutral. I shut off all the breakers at the
panel except the breaker for the problem outlet. The voltage readings
do not change. I then shut off the breaker for the problem outlet (all
breakers now off) and the outlet now shows zero voltage between all
wires. The voltages at the panel appear normal. Also: there is no
continuity between ground and neutral at the problem outlet. This would
suggest an open neutral, but what would cause the voltage differentials
on the neutral wire if it was open? There isn't an obvious back load
soure such as an appliance.

I'm going to attempt to find out where the branch ties in, but it's a
1950's split level with pretty inaccessible wiring. I hate older
houses... help!

-T
Buy one of those test plugs that will show what is miswired or most likey
open then replace the outlet.
 
C

CJT

ToMh said:
Buy one of those test plugs that will show what is miswired or most likey
open then replace the outlet.
I don't see how that will tell anything not already known.
 
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T

Tuyen

Mark said:
Open neutral. Induced voltage.
That would definitely explain zero voltages when breaker is off. And if
I short neutral and ground there's only 0.06 mA flowing.

So: given the induced voltages and wire guage is it possible to figure
out approximately how far back is the break in the neutral wire?

I removed the receptacle and am making all readings with the bare
wires.

Thanks for all the fast responses!

-T
 
B

Bud--

Digital meter are very high input resistance and can easily indicate
phantom voltages. Neon lights are not as bad but also can indicate. Plug
in receptacle testers also operate at very low current. If they indicate
an outlet is bad it probably is. If they indicate an outlet is good it
isn't necessarily. They particularly can't be relied on to test for a
good ground.
That would definitely explain zero voltages when breaker is off. And if
I short neutral and ground there's only 0.06 mA flowing.

So: given the induced voltages and wire guage is it possible to figure
out approximately how far back is the break in the neutral wire?
I don't thinks so.

Look in other boxes with devices on the same breaker. It will probably
be toward the panel. Likely possibilities are back-stabbed receptacle
through connections (good idea to convert them all to connection under
screw) or loose wire in a wire nut.

bud--
 
K

Kevin Ricks

Tuyen said:
I have a problem outlet that reads 30V (digital voltmeter) between
neutral and ground, 88V between hot and neutral and 120V between hot
and ground. The outlet is on a branch circuit; it appears to be the
only outlet on the branch. Other branches of the circuit show the
normal 120V between hot and neutral. I shut off all the breakers at the
panel except the breaker for the problem outlet. The voltage readings
do not change. I then shut off the breaker for the problem outlet (all
breakers now off) and the outlet now shows zero voltage between all
wires. The voltages at the panel appear normal. Also: there is no
continuity between ground and neutral at the problem outlet. This would
suggest an open neutral, but what would cause the voltage differentials
on the neutral wire if it was open? There isn't an obvious back load
soure such as an appliance.

I'm going to attempt to find out where the branch ties in, but it's a
1950's split level with pretty inaccessible wiring. I hate older
houses... help!

-T
When you have an open neutral then the voltage readings are unpredictable
depending on what is connected down stream. For example a light bulb will
connect hot to the open neutral. Even though the bulb will not be lit
(switch on), you will get voltage in the open neutral via the bulb filament
.. An outlet tester as someone suggested will not give correct readings
unless you remove or turn off all loads on that circuit. Sometimes this is
hard to do if you have direct wired or hidden stuff on the circuit such as
smoke alarms, or a doorbell transformer etc.

It is also possible that your neutral connection somewhere has a high
resistance connection. Where the wires are loose and overheated, a carbon
bridge may let some current through giving the strange reading.

Kevin
 
S

Sev

2nd thought, think it'sgot to be open neutral, as Mark says. Think I
was off the beam with that first post. So your looking for loose
wires(white) as you trace that branch back, or back stabbed receptacles
as said above.
 
T

Tom The Great

I have a problem outlet that reads 30V (digital voltmeter) between
neutral and ground, 88V between hot and neutral and 120V between hot
and ground. The outlet is on a branch circuit; it appears to be the
only outlet on the branch. Other branches of the circuit show the
normal 120V between hot and neutral. I shut off all the breakers at the
panel except the breaker for the problem outlet. The voltage readings
do not change. I then shut off the breaker for the problem outlet (all
breakers now off) and the outlet now shows zero voltage between all
wires. The voltages at the panel appear normal. Also: there is no
continuity between ground and neutral at the problem outlet. This would
suggest an open neutral, but what would cause the voltage differentials
on the neutral wire if it was open? There isn't an obvious back load
soure such as an appliance.

I'm going to attempt to find out where the branch ties in, but it's a
1950's split level with pretty inaccessible wiring. I hate older
houses... help!

-T

If this was me, I would go to the panel and check for all the neutrals
being secured.

It sounds like a floating neutral somewhere.

IMHO,

tom @ www.NoCostAds.com
 
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T

ToMh

CJT said:
I don't see how that will tell anything not already known.
These are a cheap, and a easy way to verify that the outlet is wired
correctly, and changing the outlet will more than likely solve the problem.
 
T

ToMh

ToMh said:
These are a cheap, and a easy way to verify that the outlet is wired
correctly, and changing the outlet will more than likely solve the
problem.
Oh sorry, I didn't catch that you had already removed the receptacle. You
say it's a branch circuit, are you sure about this, and that it's not just
the last receptacle on the line? If it is a branch, do you know were the
branch is. If it's wired to another receptacle, then that probably were the
problem is, else it's in the branch. Hopefully it's not some hack job buried
in the wall. If you can't find the branch, you may want to just open up each
receptacle on the bus and look for a an extra set of wires branching off of
that receptacle.
 
C

CJT

ToMh said:
These are a cheap, and a easy way to verify that the outlet is wired
correctly, and changing the outlet will more than likely solve the problem.
I doubt it, given the situation described.
 
C

CJT

ToMh said:
Oh sorry, I didn't catch that you had already removed the receptacle. You
say it's a branch circuit, are you sure about this, and that it's not just
the last receptacle on the line? If it is a branch, do you know were the
branch is. If it's wired to another receptacle, then that probably were the
problem is, else it's in the branch. Hopefully it's not some hack job buried
in the wall. If you can't find the branch, you may want to just open up each
receptacle on the bus and look for a an extra set of wires branching off of
that receptacle.
Oops, I responded too quickly to your previous post.
 
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M

mm

I have a problem outlet that reads 30V (digital voltmeter) between
neutral and ground,
Try with an analog meter, although not an FETVOM.

88V between hot and neutral and 120V between hot
 
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