ghost voltage

Old 11-05-19, 05:51 PM
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ghost voltage

I have old fan which i recently serviced. For kicks i measured between the fans metal housing and a grounded conduit and i got like 30vac. My meter has a low z function and when i set it to that it read 0 vac. I trust that the the 30 vac was just ghost voltage.

So why does that occur? Close proximity to the motor of the fan perhaps? Ungrounded non polarized plug?

Is a low impendace meter fool proof?
Old 11-05-19, 06:08 PM
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Does your fan have a ground prong? I'm pretty sure it doesn't.
In that case, it is either floating or connected to neutral. In your case, it probably is floating (not connected to anything).
That will just give you some random voltage as potential of the case can be anything depending on many factors.
Digital multi meters have very high impedance and that is why you are able to measure this kind of ghost voltage.

Low Z mode will put some high resistance in between the probes and that allows low energy potentials like ghost voltage to dissipate.
Old 11-05-19, 07:22 PM
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If you have a wire with AC on it running beside another wire, the electromagnetism of the AC induces a voltage in the other wire but there is no real power (current).

This is basically how a transformer works but with much longer wires interacting so there is a current produced.

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