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.

I'm not surprised. It's close to impossible to find a web site that doesn't totally ignore the downstream ground-neutral fault detection, even though it has been built into GFCIs for well over 10 years. The app note for the GFCI chip describes how an oscillation is induced that indirectly measures the downstream ground-neutral resistance. The grounded neutral detection is resistance based, the trip spec being 2 ohms. Here's one web document that includes the grounded neutral detection: https://www.nema.org/Products/Documents/NEMA-GFCI-2012-Field-Representative-Presentation.pdf