eric stromberg said:
. . .imho, GFCIs should really be called something like "Current imbalance detectors" because they really have nothing whatsoever to do with "Ground." They sense the imbalance between the hot and neutral conductor and the internal test switch works by shunting some current around the internal sensing CT. There is no way an external tester can access the internal connections on either side of the sensing CT.
Eric Stromberg, P.E.
I agree that the external tester doesn't test the integrity of the ground; it's just assumed.
But an imbalance between the hot and neutral has everything to do with the ground. That's because the neutral is grounded. Receptacle systems are referenced to ground. If you've ever worked on an ungrounded delta system you know what I mean. You can put a tester on any of three phases to ground and it will read nothing. It only returns current through the phase wires and nothing else.
So on a normal receptacle system that is referenced to ground, any unequal current between hot and neutral *has* to be flowing to ground, and is always a ground fault condition. That's why it is a shock hazard. If you touch something grounded and touch a hot wire you get shocked. If you are grounded and touch a hot wire on an ungrounded system you won't get shocked. If receps weren't referenced to ground, you would have to touch two wires to get shocked, not just one.
Referencing the whole system to ground simplifies shock protection because any type of fault has only one place to go; the ground.
