"Joseph Meehan" wrote:
Robert11 wrote:
Hello:

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 ?

Thanks,
B.


If you find an old analog meter and test it again you will likely see no
voltage. Those new digital meters read voltages that get into a wire just
because it is close to another wire and does not have anything to draw the
current voltage down; much like a static charge.

On a neutral? Yeah, you'll get that effect on a floating wire (a switched-off
hot, for example), but the neutral is hard grounded at the panel.