Andy Hill wrote:
"Robert11" wrote:
Have been trying to get some smoke detectors interconnected, and
during the trouble shooting of the problem, I measured (with an
analog voltmeter) the
voltage between the white neutral, and the bare copper ground wire
in the box.

Was very surprised to see that it was about 2 V AC.

Other than the fairly obvious reasons, such as bad ground
connections in the service box for the neutral or gnd, or within the
wiring chain itself, was wondering if anyone might have any other
thoughts or opinions on this.

Might as well add this: The smoke detectors were on line, and
functioning, when I measured.
The interconnect for the smoke detectors (the third, red, wire )
uses the white neutral (also)
as it's return. And, measuring a few outlets around the house
showed 0 voltage between the neutral and gnd as one would expect.

But, even if the smokes were dumping something on the white neutral,
it being at gnd potential, would "sink" these voltages immediately,
I would think, if the neutral was grounded well.
So, what might be happening ?

BTW: How "common" is it to see voltages of this magnitude between
the white neutral and ground ?

If you have a large load upstream from the smokes on the circuit,
it's possible to get a couple of volts on the neutral relative to
ground. In that case, no big.

However, if the smoke detectors are on their own circuit, or you
don't have a large load on the circuit, then you've got a loose
splice on the neutral somewhere between the measurement point and the
grounding bar in the breaker box. Not quite a floating neutral, but
thinking about it. Real fun to track down, especially since you
usually don't know the wire routing.

I did not note in in my other response, but this is certainly possible
and it could be a real problem. I did not really think about it with my
first response, but should have. It can be a dangerous situation. So it is
worth checking out to make sure what it is.

--
Joseph Meehan

Dia duit