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 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 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
