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
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