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Ignoramus22165 Ignoramus22165 is offline
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Default Phantom voltage in a disconnected busbar?

On 2015-06-05, Lloyd E. Sponenburgh lloydspinsidemindspring.com wrote:
Ignoramus22165 fired this volley in
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But I am still wondering how, on a disconnected busbar, I would read
that phantom voltage. Was that just electromagnetic induction?

It is still a mystery to me.

The biggest question is how come it was only on one of the two
identical boxes.


The real first question is, "what was your reference"?


Bus to bus and bus to ground

Then, following that up some: Were you measuring bar to 'local
ground', bar to bar, bar to box neutral? Was this single-phase, or
three-phase?


All of them had voltage and to ground also.

What's the input impedance of your meter? Did you try a microscopic load
-- like (say) a couple-hundred K-ohms across the meter leads? You might
have a very high input impedance meter, and just be measuring "antenna
effect" to some nearby physically parallel live circuit.


This is my own explanation. I did not want to stick anything across
the leads, however.

There might be the residue from an old arc in that box that left some
slightly-conductive metal/metal oxides plated in and around the
insulators of the box.


This is something that I did not consider, but it also makes good
sense.

It would also provide for serious arc flash hazard, if
disconnected under load.

480 volts + 500 kVa + big busbars == arc flash hazard

i