jim dungar said:
Larry, GFCIs do not need a ground reference to function. If there is not a complete circuit then current will not flow and the GFCI will not trip, but it is not because there is no dirt. GFCIs function just fine in my wooden floor kitchen or on the 25th floor of a high rise, neither of which have dirt in their fault path.
It doesn't have to be 'dirt'
per se, but there has to be a connection between one circuit conductor and whatever coductive surface (i.e., the aforementioned 'ground plane') one might contact while making accidental contact with the other (i.e., the 'hot') circuit conductor.
A GFCI only works if it's connected to a supply with a grounded conductor. By grounded, I mean whatever surface one might be in contact with when the accidental touch occurs. In a non-grounded supply, there's no electrocution hazard for the same reason the first ground fault doesn't trip a breaker.
I'm making no reference to the circuit EGC, but it's the grounding electrode system connected between the earth, concrete, metal floor, airplane body, etc., and the supply's grounded conductor that allows current to flow through a person's body.
In other words, yes, GFCI's do need a ground reference in the sense that the 'ground' must be part of the circuit included in the shocking-current pathway. Your kitchen floor, if dry, is not conductive enough for accidental contact with a hot wire to trip a GFCI.
But, if your supply was non-grounded, then stepping barefooted on a wet concrete floor slab on grade, or even a well-grounded metal floor, would not electrocute you during contact with a hot wire. There must be a pathway to one conductor for contact with another to be hazardous.
Unless you're touching a system's neutral, contact with a system's hot does not create a closed circuit through your body. Current will not enter your body unless it has a pathway through you back to the source. You won't get a shock, and a GFCI will not trip, without such a pathway.
To protect you against electrocution when standing on earth, the system requires an earth connection. To protect you while in contact with supposedly-bonded metallic surfaces, they system must have a connection to those surfaces. It doesn't have to be earth.
It does, however, have to be whatever you're in contact with during the accidental contact with an energized part. It's handy and convenient to use the earth, because so much of our environment is, or is bonded to, the earth. What creates the hazard also provides the means for the protection to work.
