James, On Monday 21 March 2005 03:55, James Knott wrote:
John Sowden wrote:
Note: A ground fault interupter is designed to sense a small current flow from the hot side (not neutral) to ground. There should never be a current flow through this path . . .
I thought they detected a current imbalance in the hot & neutral conductors. It is possible to have leakage to other than ground.
Correct (well, half correct). They're often used when there is no ground reference lead in the building's wiring system. However, there is no other leakage path than to ground (however indirect or--no pun intended--circuitous that path is). GFCIs essentially _infer_ that current is traveling to ground because there's unequal current flow through the two power wires. (Kirchoff's laws to the rescue). The _assumption_ (a conservative one) is that the current is flowing through a human. Humans are notoriously ill-suited for use as electrical conductors. Hmmm... I wonder, how do GFCIs deal with reactive loads? Do they time average the current measurement over several cycles? Randall Schulz