# Voltage Between White Neutral And Gnd Wire Question In House Wiring ?

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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.

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V = I x R

The neutral is not a magic, superconductor. It has resistance. It and the grounded conductor are only bonded (according to US code) at a single point in the service panel. A current flowing on the neutral will cause a voltage between any point and the ground bonding point. The higher the current, and the farther from the panel, the higher the voltage.

Charles Perry P.E.

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To summarize what Charles Perry has stated - electricity at both ends of a wire is not same. Wire is another electrical component in that circuit. However if smoke detectors (on a

15 amp circuit) created 2 volts difference, well, be suspicious. Smoke detectors draw so little current. Voltage difference should not be that large between neutral and safety ground wire. 2 volts is not considered dangerous. But the difference should not be that large.

Verify all connections on neutral and ground wires between smoke detector and breaker box. Use the meter, as you did, to learn voltage difference at each wire junction all the way back to breaker box AND inside breaker box. Locate a loose connection - most likely on neutral wire.

Again, there is no such thing as a conductor. Even wire is an electronic device. It has inductance, capacitance, and resistance. How much? This is why numbers are so important AND why you must never assume voltage is same at both ends of a wire.

Both safety ground and neutral wire jo> Have been trying to get some smoke detectors interconnected, and

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You don't, by chance, have some other things on this circuit?

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| V = I x R | | The neutral is not a magic, superconductor. It has resistance. It and the | grounded conductor are only bonded (according to US code) at a single point | in the service panel. A current flowing on the neutral will cause a voltage | between any point and the ground bonding point. The higher the current, and | the farther from the panel, the higher the voltage.

And this is the voltage drop. So if he really has 2 volts on there (assuming this isn't phantom voltage for some reason), then he has 2 volts drop on just the neutral, and probably another 2 volts drop on the line wire.

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