An entire 15amp circuit is shutting off at my house without blowing its fuse
and I'm going nuts trying to find the cause. My house is old, and the
ungrounded wiring, (consisting of just a hot and an neutral conductor
without a separate grounding conductor), is deteriorated to the point that
the insulation on the conductors will break and fall off if not handled very
carefully. The problem circuit turns off, and turns on for no apparent
reason. I noticed that when the circuit is on, a 50 volt potential exists
between the neutral conductor at a certain light fixture and its metal bx
conduit, measured with a multi meter. There's also 50 volts between the
metal conduit and the neutral wire from another, properly working circuit,
and no volts between the two neutrals, so it seems that the bx conduit is
what is charged and not the neutral. So it seems that voltage is "leaking"
from the hot lead into the conduit. But why just 50 volts and not the
entire line voltage of 120 volts? Is there any other explanation?

Another strange thing is that there is about 50 volts between the two leads
that bring power to a different overhead light fixture when the switch that
controls the light IS TURNED OFF. When the switch is on, the voltage
between the leads is 120 volts, just like you would expect, but it reverts
to 50 volts when the switch is off.

Any advice anyone can give me will be appreciated.

Tom
Durham, North Carolina

Your wiring is not ungrounded, it's grounded through the armor of the cable.
You are experiencing an open neutral situation, which is why the odd voltage
readings. You need to find all the outlets on the affected circuit then
locate the one where the neutral connection has deteriorated and correct it
"Tom Desmond" wrote in message
...
An entire 15amp circuit is shutting off at my house without blowing its
fuse and I'm going nuts trying to find the cause. My house is old, and
the ungrounded wiring, (consisting of just a hot and an neutral conductor
without a separate grounding conductor), is deteriorated to the point that
the insulation on the conductors will break and fall off if not handled
very carefully. The problem circuit turns off, and turns on for no
apparent reason. I noticed that when the circuit is on, a 50 volt
potential exists between the neutral conductor at a certain light fixture
and its metal bx conduit, measured with a multi meter. There's also 50
volts between the metal conduit and the neutral wire from another,
properly working circuit, and no volts between the two neutrals, so it
seems that the bx conduit is what is charged and not the neutral. So it
seems that voltage is "leaking" from the hot lead into the conduit. But
why just 50 volts and not the entire line voltage of 120 volts? Is there
any other explanation?

Another strange thing is that there is about 50 volts between the two
leads that bring power to a different overhead light fixture when the
switch that controls the light IS TURNED OFF. When the switch is on, the
voltage between the leads is 120 volts, just like you would expect, but it
reverts to 50 volts when the switch is off.

Any advice anyone can give me will be appreciated.

Tom
Durham, North Carolina

Tom Desmond wrote:

An entire 15amp circuit is shutting off at my house without blowing its fuse
and I'm going nuts trying to find the cause. My house is old, and the
ungrounded wiring, (consisting of just a hot and an neutral conductor
without a separate grounding conductor), is deteriorated to the point that
the insulation on the conductors will break and fall off if not handled very
carefully. The problem circuit turns off, and turns on for no apparent
reason. I noticed that when the circuit is on, a 50 volt potential exists
between the neutral conductor at a certain light fixture and its metal bx
conduit, measured with a multi meter. There's also 50 volts between the
metal conduit and the neutral wire from another, properly working circuit,
and no volts between the two neutrals, so it seems that the bx conduit is
what is charged and not the neutral. So it seems that voltage is "leaking"
from the hot lead into the conduit. But why just 50 volts and not the
entire line voltage of 120 volts? Is there any other explanation?

Another strange thing is that there is about 50 volts between the two leads
that bring power to a different overhead light fixture when the switch that
controls the light IS TURNED OFF. When the switch is on, the voltage
between the leads is 120 volts, just like you would expect, but it reverts
to 50 volts when the switch is off.

Any advice anyone can give me will be appreciated.

Tom
Durham, North Carolina




This may not answer all your questions.

But, if you are using a solid state digital voltmeter....

Hopefully, you understand why that kind of meter's extremely high input
impedance combined with capacitive coupling of ac signals between
powered and unpowered conductors can let the meter display voltage
readings which are accurate but exist only because there's just
microamps of current flow.

If you don't understand those principles, learn about them or you'll be
following false trails which will lead you to incorrect conclusions.

HTH,

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."

Either of the replies you got could be right. Or it could be something else
entirely.

You say there is no voltage between neutrals. Neutrals on different
circuits, or the same circuit?

What is the voltage between the hot and the conduit?
How about voltage between the hot, the neutral, and the conduit to a
grounded water pipe?

You must have a bad connection or a short or both. It is probably an easy
fix, but you have to find it first. If it was me, and I wasn't sure I knew
what I was doing, I would leave the breaker open until an electrician had a
look at it.

Tom Desmond wrote (in part):

My house is old, and the
ungrounded wiring, (consisting of just a hot and
an neutral conductor
without a separate grounding conductor), is
deteriorated to the point that
the insulation on the conductors will break and
fall off if not handled very
carefully.

Turn the circuit OFF and call a qualified electrician. Your problem is
not DIY! Old BX cable is known to rust and cause fire hazards because
the rusting causes the impedance of the armour to be so high that the
breakers or fuses won't trip. The symptoms that you describe may be an
indication of such. The problem may be something as simple as a bad
connection, but, IMHO, you need an electrician. I have a master
electrician's license in two states, both of which would condemn your
home if code enforcement caught wind of it. Not trying to be negative,
just safe.

On Wed, 15 Jun 2005 23:25:56 -0400, Jeff Wisnia
wrote:

Tom Desmond wrote:

An entire 15amp circuit is shutting off at my house without blowing its fuse
and I'm going nuts trying to find the cause. My house is old, and the
ungrounded wiring, (consisting of just a hot and an neutral conductor
without a separate grounding conductor), is deteriorated to the point that
the insulation on the conductors will break and fall off if not handled very
carefully. The problem circuit turns off, and turns on for no apparent
reason. I noticed that when the circuit is on, a 50 volt potential exists
between the neutral conductor at a certain light fixture and its metal bx
conduit, measured with a multi meter. There's also 50 volts between the
metal conduit and the neutral wire from another, properly working circuit,
and no volts between the two neutrals, so it seems that the bx conduit is
what is charged and not the neutral. So it seems that voltage is "leaking"
from the hot lead into the conduit. But why just 50 volts and not the
entire line voltage of 120 volts? Is there any other explanation?

Another strange thing is that there is about 50 volts between the two leads
that bring power to a different overhead light fixture when the switch that
controls the light IS TURNED OFF. When the switch is on, the voltage
between the leads is 120 volts, just like you would expect, but it reverts
to 50 volts when the switch is off.

Any advice anyone can give me will be appreciated.

Tom
Durham, North Carolina




This may not answer all your questions.

But, if you are using a solid state digital voltmeter....

Took the words right outta my mouth.

Use an analog meter, a cheapie, or better a Simpson 260 for this stuff
and not be taken in by vapor volts.


Hopefully, you understand why that kind of meter's extremely high input
impedance combined with capacitive coupling of ac signals between
powered and unpowered conductors can let the meter display voltage
readings which are accurate but exist only because there's just
microamps of current flow.

If you don't understand those principles, learn about them or you'll be
following false trails which will lead you to incorrect conclusions.

HTH,

Jeff

According to volts500 :
Tom Desmond wrote (in part):

My house is old, and the
ungrounded wiring, (consisting of just a hot and
an neutral conductor
without a separate grounding conductor), is
deteriorated to the point that
the insulation on the conductors will break and
fall off if not handled very
carefully.

Turn the circuit OFF and call a qualified electrician. Your problem is
not DIY! Old BX cable is known to rust and cause fire hazards because
the rusting causes the impedance of the armour to be so high that the
breakers or fuses won't trip. The symptoms that you describe may be an
indication of such. The problem may be something as simple as a bad
connection, but, IMHO, you need an electrician. I have a master
electrician's license in two states, both of which would condemn your
home if code enforcement caught wind of it. Not trying to be negative,
just safe.

I agree with volts500. Your system has deteriorated to the point
where you shouldn't be bothering to diagnose and pinpoint faults.
Instead, you should be replacing whole circuits. If you understand
wiring well enough to do it yourself, fine, but otherwise, you
need professional assistance.

Unless that 50V is a phantom high impedance mismeasurement, the
whole circuit is likely unsafe.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

Chris Lewis wrote:
According to volts500 :

Tom Desmond wrote (in part):



My house is old, and the
ungrounded wiring, (consisting of just a hot and
an neutral conductor
without a separate grounding conductor), is
deteriorated to the point that
the insulation on the conductors will break and
fall off if not handled very
carefully.



Turn the circuit OFF and call a qualified electrician. Your problem is
not DIY! Old BX cable is known to rust and cause fire hazards because
the rusting causes the impedance of the armour to be so high that the
breakers or fuses won't trip. The symptoms that you describe may be an
indication of such. The problem may be something as simple as a bad
connection, but, IMHO, you need an electrician. I have a master
electrician's license in two states, both of which would condemn your
home if code enforcement caught wind of it. Not trying to be negative,
just safe.


I agree with volts500. Your system has deteriorated to the point
where you shouldn't be bothering to diagnose and pinpoint faults.
Instead, you should be replacing whole circuits. If you understand
wiring well enough to do it yourself, fine, but otherwise, you
need professional assistance.

Unless that 50V is a phantom high impedance mismeasurement, the
whole circuit is likely unsafe.

I agree with Chris Lewis. This looks like a dangerous situation. In
the automotive world we call it a "resistive" short. The problem is
resistance creates heat. You could be at 50V because the other 70V is
burning off in the form of heat somewhere. Thats one way to find the
problem actually. But I'm sure you agree if this is a resistive short
its quite dangerous.

Also the random on/off points to a short. If the conduit is charged,
and if current is bleading off, then you definitely have a resistive short.

I just moved from a home with same old wires that deteriorated in my
hand. Not recommended but if you want too look I would open up each box
on the circuit. Often for instance, they will wire to 1 electrical
outlet, and double connect on the terminals, and run wire from that to
another box. Those double connections can develop resistance. They
could do this on a switch, or an outlet. Its rare on lamps and fans
where they tend to use twist caps as opposed to doubling up on the screw.

--
Respectfully,


CL Gilbert

"Verily, verily, I say unto you, He that entereth not by the door() into
the sheepfold{}, but climbeth up some other *way, the same is a thief
and a robber."

GnuPG Key Fingerprint:
82A6 8893 C2A1 F64E A9AD 19AE 55B2 4CD7 80D2 0A2D

For a free Java interface to Freechess.org see
http://www.rigidsoftware.com/Chess/chess.html