blueman wrote:
I was working last night on an electrical circuit that was shut off at
the breaker.

Nevertheless, the voltage from neutral to ground and from hot to
ground both measured about 30V. This was enough to cause my voltage
probe to buzz and to even cause a compact flourescent to light
dimly. The current across the circuit however measure just 0.7 mA.

Am I correct in assuming that this is probably just induced voltage
from neighboring wires that run alongside it or is there potentially
something more serious and sinister going on?

Thanks!


Measuring 30 volts from hot to ground with a high impedance voltmeter
can easily be caused by capacitive coupling to that that wire from
another wire in close proximity carrying full voltage. It's a common
question posed here. It could also occur if the breaker had popped under
overload many times and had a very high resistance leakage path inside
it through deposited vaporized contact material.

But, if you really measured 30 volts from neutral to ground (and didn't
intend to say that the measurement was from hot to ground.) then
there's something seriously wrong because the neutral should be at
ground potential, and there's no way that 700 microamps of capacitive
coupling or leakage is going to create 30 volts between two wires which
are connected together.

Better measure again to be sure, and if you still get 30 volts between
neutral and ground, my guess is that the ground lead ISN'T really
grounded and you're seeing an induced voltage on it too, relative to
neutral. THAT could be sinister.

Let us know what you find,

Jeff
--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"