Some of you may recall my previous post about a ~20V potential between my electrical ground and my concrete slab. That’s still not resolved - it’s currently sitting just under 10V.
Today I have a new mystery - to me anyway…
I’m sitting at my desk and notice that I got a tingle from the outer shield/shell of a USB-C cable. I got my multi-meter and measured 65V from the cable to me with my bare feet on the slab! It drops to about 16V if I lift my feet off the floor. I immediately assumed the charging brick it’s plugged into was faulty, but just in case I took a more measurements and found that the another similar charger has a similar offset, the “ground” part of a TRS cable plugged into an amplifier is similar, the accessible metal shield part of a USB-A port on an ASUS ChromeBox is similar. I assume that’s not normal?
This is a new slab on grade build. Ground and neutral are properly bonded - I checked a few outlets and ground to neutral is ~0.3V.
Edit - I don’t think there is any safety risk - I measured 0.3μA current.
I have two grounding rods and I believe they are good - they are now buried under foam insulation and gravel so I can’t (easily) check them, but the electrician that wired my house assured me it was OK to bury them. I was a bit paranoid about burying them and checked and double checked that they were both firmly connected before backfilling gently with a shovel. Is it possible my earth ground (gravel fill) just isn’t conductive enough? As I said to someone below - I measure 5V from the electrical ground to earth ground (literally just sticking my meter probe in the earth) right near where the grounding rods are installed.
That sounds like a fine setup. Passable grounding could give 5v if somewhere in the ballpark of 200mA are passing through it. Reading through maybe the generator has a short to ground.
Edit: the only place ground and neutral are connected is in the main breaker panel, correct?