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.
What is the grounding situation at the panel? Seems like your electrical ground has no path to earth ground. Maybe the lug on the grounding rod loosened off after inspection.
This needs to get fixed quick. Even 10mA can cause serious problems. Without a safe ground your whole house is a minefield.
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?