On Thu, 23 Feb 2006 16:25:20 GMT, Rich256 wrote:

Ignoramus15109 wrote:
snip

This brings to mind something I encountered a couple years ago. Someone
in a Campground tripped the Camp Group power GFCI when he plugged in his
Travel Trailer. He said it did not happen when he used it at home and
other places (that did not have GFCI).

The problem was that the Ground and Neutral wires were tied together
inside the trailer. Of course the Ground and Neutral were also tied
together in the Campground. Therefore some of his return current was
flowing in the Ground tripping the GFCI.

Same thing was happening in the drill but only a tiny bit was probably
flowing through the carbon dust but it was enough to cause the GFCI to trip.

A GFCI works because in a single phase circuit that is working
properly, the current in the neutral must match the current in the hot
conductor. When both conductors are passed through a coil, the coil
won't energize because there is no current imbalance. If some of the
current has a different path to complete the circuit, then there will
be a net difference in current at the sensing coil, and it'll trigger.
That's why GFCI's work on two wire cords just as well as grounded
cords.

Pete Keillor