GFCI and an Open Ground

road-runner wrote:

wnjj wrote:


The "different mechanism" described in that document still uses the current imbalance detector; there is only one detector transformer.

OK, guess I was careless with the semantics. You're right, there's only one transformer. It has two coils, one of which is used in both the ground fault detection and grounded neutral detection. The other coil is used only for grounded neutral detection. What I'm trying to convey is that the grounded neutral detection has led to the addition of a second sensing coil physically surrounding the hot and neutral conductors.

Maybe it is semantics but you did say that it "does not use the current imbalance detector" and I disagree.

The additional neutral coil isn't a sensing coil but rather a driving coil. A signal is driven onto it to attempt to induce current in the netural/hot lines. The other coil always does the sensing regardless of whether the mismatched current is caused by an external source (e.g. a person shunting some through their body) or from the induced current in the ground loop formed by a neutral/ground fault.

Again, thanks for making me curious enough to study it. The link you provided was very helpful. :)