Dave Schwartz wrote:
I have a series of 5 or 6 120V AC patio lights, controlled by a ground
fault which has been working fine for years. Now, this season, after
1-2 hours, the ground fault trips, and I cannot reset it for hours.
If there was a short, it would trip immediately, right? What would
be the condition that would cause it to trip a few hours later, and
then not reset? Thanks

It would appear that something is causing a ground fault (not a short)
based on heat. Something may be expanding as it heats up and causing the
ground fault. Try removing some of the lamps from the circuit and see it it
still happens. You may be able to do it by just removing the bulbs or you
may need to disconnect the wires.

It is also possible the GF unit is defective and needs to be replaced.

--
Joseph Meehan

Dia duit