On 21/12/2019 15:58, Ralph Mowery wrote:
In article ,
says...
Actually that problem typically occurs with a VOM with a high impedance.
You could use a $150 Fluke which is a very real meter and see spurious
voltage. You won't see it with an old meter with a needle movement,
because it's not high impedance. I've never seen it with a cheap neon tester
either, they take substantial voltage to light, eg 90V, and do pass
some amount of current, so I think it's unlikely you could get it to
light from spurious voltage due to a nearby cable. The non-contact
type testers could light.




I have seen the neon testers light up with no real current on the wires.

Where I worked many wires were in conduit and you could disconnect each
end and the neon tester would light from one wire to the ground
(conduit). A Fluke meter would show about 115 volts. My 'trusty'
Simpson 260 analog would show about 75 volts on the 250 volt scale. One
way I found to tell if the voltage was 'induced' was to start off on
the highest scale of the Simpson, then switch to the lower ranges. If
induced, the meter would stay about the same physical place on the
scale. If 'real' it would show the same actual voltage.
Some of the wires had enough current on them they would give you a very
bad shock.

Some switches and relay contacts had capacitors and resistors across
them to supress arking. The neon testes could be fooled by those.

You have neon testes?
(Sorry couldn't resist) :-)

--
Bod