The Truth About GFCIs — UL 943, Floating Generators, Bonding & Current Paths

The Truth About GFCIs — UL 943, Floating Generators, Bonding & Current PathsThere may be more misconceptions about GFCIs than almost any other electrical safety device.

Does a GFCI need an equipment grounding conductor to work?

What does the toroidal sensing coil actually monitor?

Why might a GFCI behave differently on a truly floating generator?

And what happens when a bonded-neutral generator is connected to a dwelling through an interlock where the neutral is not switched?

In this episode, Paul Abernathy breaks down the actual operating principles behind UL 943 Class A GFCIs and explains why understanding the current path is far more important than simply memorizing terms like “grounded,” “bonded,” or “floating.”

We explore how a GFCI compares current leaving and returning through its monitored conductors, why an equipment grounding conductor is not required for differential-current sensing, and why a GFCI should never be thought of simply as a device that “detects current going to ground.”

You'll also learn why a truly floating generator may have little or no first-fault current path, how a second fault can completely change that condition, and why connecting a generator to a dwelling can change its electrical relationship to ground.

Then we tackle one of the most misunderstood generator issues in the trade:

Bonded neutral vs. floating neutral.

If a generator is connected through an interlock or transfer arrangement that does not switch the neutral, the generator neutral remains connected to the dwelling's grounded conductor system. Adding another neutral-to-ground bond at the generator can create parallel paths for normal neutral current through equipment grounding and bonding conductors.

We also cover:How a GFCI's toroidal current transformer actually worksThe difference between GFCI protection and overcurrent protectionWhy a GFCI can work on a circuit with no EGCWhy “GFCI protected” does not mean “equipment grounded”Why touching hot and neutral can still produce a dangerous shock without creating a GFCI-detectable imbalanceWhy some plug-in GFCI testers may not operate properly on an ungrounded circuitThe difference between the integral TEST button and an external testerFloating generators and first-fault conditionsBonded-neutral generatorsSwitched vs. unswitched neutralsSeparately derived generator systemsParallel neutral-current pathsWhy a ground rod is not the normal branch-circuit fault-current return pathHow grounding, bonding, GFCI pr