Joseph Meehan wrote:

Andy Hill wrote:

"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.


Well .. We are only talking 2 Volts. I suspect you might be able to get
2Volts, but I have not done the math and I would not be the house on it.

Don't even bet a penny on it unless the neutral is OPEN on its way back
to the panel. The capacitive currents are in the microamp range and it
takes LOTS of ohms to create a two volt drop ant those current levels.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

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