Volt. Appearing Between White Neutral And Gnd Wire ?

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  #1  
Old 04-27-05, 05:18 AM
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Volt. Appearing Between White Neutral And Gnd Wire ?

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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  #2  
Old 04-27-05, 05:21 AM
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You shouldn't be seeing this. Try cutting the circuit off and measure resistance between the ground and neutral.
 
  #3  
Old 04-27-05, 09:27 AM
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It is not unusual to have a couple of volts between neutral and ground, since the neutral conductor is carrying current and has an impedance (resistance) back to the source where the current is returning.
 
  #4  
Old 04-28-05, 03:26 AM
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I just measured 0.9 V at my house, so 2V does not seem out of line. IIRC, I have measured over 10V at a former workplace (but my memory isn't what it used to be, so take that with a grain of salt).
 
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