2014 NEC, 406.4(D)(2) Non–Grounding-Type Receptacles.

[jap]

Yes, but neither of the conductors the GFCI is monitoring is grounded. The neutral in the panel is just for the electronics.

Likewise, for a 120 volt GFCI, it wouldn't care if either of the conductors it is monitoring are grounded or not. The 120 volt model wouldn't care if the electronics were powered by a 110-volt DC battery!

IMHO.

If one of the conductor in the 120v models being monitored wasn't grounded, you wouldn't have a 120v circuit to begin with.


JAP>

 

[LarryFine]

How about a 240 volt GFCI-- Only neutral involved is in the breaker box to power the electronics in the GFCI. Black wire out, black wire in; no neutral anywhere; neither black is grounded. GFCI still knows when there's a fault.

Neither black is grounded, but the source neutral still is, and still needs to be, grounded. The neutral actually being used by either the GFCI or the load is not relevant.

Even if the electronics in the 2-pole GFCI worked from line to line, and there was no neutral wire to the GFCI, the source still needs to be grounded for the GFCI to trip.

 

[LarryFine]

But that would just be a design issue of the electronics inside, not a fundamental function of how it works, right?

Correct.


Added:

A GFCI will only trip if there is a current imbalance among all of the conductors passing through the current-sensing ring. That means that some current must be returning to the source along a pathway that does not pass through the ring. That means that some current is passing from a hot wire to the source through a person's body to whatever conductive surface they are touching that is directly or indirectly grounded.

That means that a supply conductor other than the hot wire being contacted is directly or indirectly connected to earth, meaning there is a conductive pathway between the contacted surface (earth, for example) and the other-than-the-hot-wire-being-contacted supply conductor. We call that non-hot conductor the neutral. If there was no grounded conductor, then contacting a hot wire and earth would not shock us.