Doug Miller wrote:

In article , Jeff Wisnia wrote:


You weren't bothered at all by his saying he measured 30 volts between
neutral and ground?


Not if he measured it with a digital meter, no.


If you weren't, then please riddle me this Doug. Why would ANY kind of
voltmeter, digital or otherwise, indicate that much voltage between
neutral and ground (That's what the OP stated.) unless there was a
serious defect in the home's wiring.


Digital meters can read voltages at *extremely* low currents. *Any* device
that produces a magnetic field can induce an electrical current on wires that
pass near it. Unexpected currents of less than line voltage, when read by
digital meters, should be verified with an analog meter before leaping to the
conclusion that there is "a serious defect in the home's wiring."



No question that magnetic fields can induce voltages Doug, but they are
unlikely to be anywhere near as large as 30 volts in house wiring
because the outgoing and return current carrying conductors are so
physically close to each other that their magnetic fields cancel almost
completely and don't leave much of a net ac magnetic field to induce a
voltage in another nearby conductor. And, I would expect that since the
ground lead is also in close proximity to the hot and neutral leads in
typical house wiring that magnetic field would induce a near equal
voltage in it too, bucking out the voltages induced in the other two
wires, leaving little voltage to measure between them.

It's genberally capacitive coupling which causes those "phantom low
current voltages" on disconnected conductors in houses.

Things can be different in industrial applications where currents can be
much higher and the wire runs a lot longer. For example, running a three
phase circuit between two boxes in three separate pieces of metal
conduit instead of a single larger conduit because a hack installer
didn't have any large enough pipe with him (and didn't know any better)
might not seem dangerous at first thought. But, as soon as some
significant currents are put through those conductors they induce
currents in the three conduits, which, since they're electrically
onnected together at both ends by the walls of the boxes, act like a
shorted 3 phase transformer secondary. The three conduits can get hot
and often will start arcing where they join onto the boxes.

At any event, the OP found the problem, an open connection in the
neutral lead at a wire nut. The degree of "seriousness" of that defect
in his house wiring is debatable.

Peace,

Jeff


Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

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