Are you isolating your DC and AC grounds? On Mar 31, 2016 4:44 PM, "Ken Hohhof" <[email protected]> wrote:
> If the two pieces of metal are not connected together, like if one of them > is floating except for stray high resistance paths to ground, then I > wouldn’t pay much attention to the voltmeter reading. Especially if you > are using a high impedance digital meter. > > Or if they are connected via a wire carrying high current, 0.1 volt may > not mean much. If you have 10 amps flowing through a wire with 0.01 ohms > resistance, there’s your 0.1 volt. > > If that second piece of metal is grounded to your common ground point with > a wire that should not be carrying any current, then I might worry about > the 0.1 volt. You might have a ground loop. > > Are you seeing a DC or AC voltage? > > > *From:* George Skorup <[email protected]> > *Sent:* Thursday, March 31, 2016 5:32 PM > *To:* [email protected] > *Subject:* Re: [AFMUG] Another ground question > > That's what i was going to say. If it's a cheap meter, don't worry about > it. Bond everything and you should be fine. > > On 3/31/2016 5:27 PM, Chuck McCown wrote: > > Depends on the meter. Does the meter read 0.0 when the leads are shorted > together? > Some meters have some random fluctuations in the least significant digit > all the time. > > *From:* Josh Baird <[email protected]> > *Sent:* Thursday, March 31, 2016 3:24 PM > *To:* [email protected] > *Subject:* [AFMUG] Another ground question > > I'm working on a new DC enclosure (steel 19" rackmount cabinet). When > using a DC volt meter, and putting the 'red' lead on a common ground point > (my ground bus, a metal rack rail, etc), and the 'black' lead on something > metal, I'm seeing ~0.1V. > > I'm assuming this is bad. On the bench currently, I have the AC ground > connected to my PSU. I have all other devices (switch, surge suppressors, > rack rails, etc) tied to a common ground that isn't yet connected to > earth. My PSU and power distribution is on a metal DIN rail which in turn > is mounted to the metal rack rails. > > Should I be concerned with this? As much as I try (or not), I still have > trouble wrapping my head around ground/ground potential/etc. > > Josh > > > > >
