My garage is not connected to my house and it's on a circuit that contains a few outlets inside the house as well. I found out the first time I tried to charge my PHEV that the entire circuit isn't properly grounded. I had an electrician come look at it, and found some old wiring that he replaced and it worked! Until it didn't… All of a sudden it wasn't grounded anymore.
The electrician came back over and when he went to test it, it was grounded properly?! Turns out this was just after a rainstorm. Now I've found this to be true that every time it rains, the garage circuit is grounded properly and when it's dry, it is un-grounded again.
Now the electrician want to tear up the underground conduit connecting the garage to the house, but I'm not sure why that would fix it? If anything I would think that it would be un-grounded when it rains, or trip the breaker every time it rains?
Also, there are no outside outlets and the underground wiring is the old metal sheathing style that runs through a 1.5" dia pipe into the house. He has already tried pulling the wire through one end with a stringer but apparently it didn't work.
Best Answer
To me it sounds like the conduit was used as the grounding conductor, as allowed by code, and it rusted through, therefore it works when the ground is wet and you have a ground connection through the soil and water. If this is the case, then an additional electrode at the garage probably won’t help as the pipe is in the ground.
Your electrician wanting to dig it up makes sense to me because when debris get in the pipe, it becomes impossible to pull new wire. With current code, the ground can be run separately, but that would be pushing the code in my opinion but legal. You can run a ground as long as they originate from the same panel.
Earth is a horrible conductor. I see high resistance quite often; this is why I don’t think another rod will help.