GFCI and an Open Ground

BB_TX wrote:

I have looked at a number of web sites and numerous GFCI diagrams and have not seen even one that had any circuit comparing neutral to ground. The only wires showing in those diagrams were hot and neutral. The circuits were comparing current flow difference between hot and neutral. And I see no way those circuits can detect impedance between neutral wire and ground wire or any additional circuits that could.
Perhaps I have not found the correct diagram to show that. Being an electrical engineer (retired) I really want to understand where that circuit resides and how it works.

Most of the explanations are somewhat simplified, and I think (though I'm not positive) that originally GFCIs only detected leakage/imbalances and nothing else.

Here's a datasheet for a GFCI chip that goes into some detail how they go about detecting a ground to neutral fault. Here's a different one that uses a bit of a different approach.