On Apr 2, 9:20*pm, wrote:
On Fri, 02 Apr 2010 15:53:44 -0800, David Nebenzahl





wrote:
On 4/2/2010 2:45 PM mike spake thus:

On Apr 2, 4:37 pm, David Nebenzahl wrote:

(This isn't to say that it isn't *possible* for a DMM to misread due to
stray capacitance or induced voltages, but it is nowhere near as
terrible a problem as you hear here.)

It *has happened to me on two different occasions. *It's also happened
to a lot of regulars here.

Maybe you have a really advanced digital meter that isn't affected.

Nope, I've got a Harbor Freight el cheapo (think I paid $3 for it). So
how is it that I got completely accurate readings of my AC line voltage
with it?

Just because YOUR cheap meter worked right when you tested YOUR
circuit doesn't mean SOME other cheap meters won't misbehave or
misread on SOME circuits - but I'd also lean towards it being a
floating neutral (did I say floating ground in my first post??? - not
sure - but floating NEUTRAL is what I meant to say.



If anything, a cheap digital VOM may be less likely to show a stray
voltage. It isn't actually a case of misbehaving or misreading.
The issue is digital VOMs have very high input impedances and hence
present virually no load to the circuit being measured. In other
words, they are taking a true measurement and NOT disturbing the
circuit. The older analog VOMs had lower input impedances. And I
wouldn't be surprised if some of the cheap $10 digital ones do too.

Still, I have to agree with David that the incidence of this occuring
may be over reported. I have an excellent Fluke VOM and can't say
I've seen this to be much of a problem. I would suspect that in at
least some cases, something other than just having a true unconnected,
floating wire picking up induced voltage is going on. Which is to
say, somehow, somewhere, that wire is connected through some high
resistance to some other live circuit.