Originally Posted by nealtw
The part I don't understand is you can still buy things with a two prong plug and with plastic plumbing the sink is not grounded so if you drop that aplience in the sink, it will trip the breaker but not as fast as gfi but the gfi will not trip.
When I put a hand mixer held by the cord into the water in a grounded concrete basement sink it didn't trip the breaker. The mixer just slowed way down because the motor cooling propeller now had to push water around instead of air so the current draw must have gone up to almost a stall current value but not enough to trip the breaker.
If that mixer were on a GFCI circuit I guess it would have tripped it, but not if
all the current coming in the hot line went back out the neutral line. The closer the mixer is to the sink drain, the more current the drain would divert from the neutral line.
A GFCI is looking for an imbalance in what goes out and what comes back and it assumes the difference it sees is due to somebody being grounded and getting a shock.
It's a differential milliammeter with a go/no-go, trip/no-trip, time-delay output, with a higher differential current giving a shorter trip time.