Mark Lloyd laid this down on his screen :
On 09/05/2016 02:31 PM, Diesel wrote:

[snip]

Umm. Unless you know something about GFCI that I don't, it's never
needed a ground wire. From what I understand, the GFCI is watching the
voltage from hot to neutral and if they become imbalanced, it trips.

Around 1995 I installed GFCI (no ground wire to or from the GFCI) for my
grandmother to use on holiday lights she put on the ground. It tripped after
a rain when some fire ants built a mound around one of the lights
(unintentional path to ground through wet soil).

Lemme guess, it was only rated for 30 ants?