Outdoor Electrical Problem

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.

Since we in NY have been having torrential rains lately, I'd guess your wiring is getting wet and tripping the gfci. Possibly when the ground water lowers, the unit can be reset. I'd pick a mid point in the string and remove the fixture and separate the wires and cap them. This will tell you where in the string the problem exists. You can keep narrowing it down like this until you find the location of the fault. Also there are special gel filled wire nuts that can be used which prevent water entry.

I expect he is correct. You should understand that nothing has to actually get wet to trip a GFCI; it is not the same as a short. I had an outlet that would trip my GFCI every time it rained, eventhough it never actually got wet. Replacing the outlet solved my problem. So, you have to identify where the problem is; and then repair or replace.

Right. But then the circuit breaker would trip, not the GFCI.

A ground fault, which is what a Ground Fault Circuit Interruptor is detecting (not a short circuit). Ground faults are typically caused by moisture, and mean that current is leaking to some source (usually the earth) besides the neutral conductor/wide slot of the GFCI outlet. This is a shock hazard, so the outlet is protecting you.

-Tim

How does heat cause a ground fault to trip? Dave Schwartz Commack, NY

I am not suggesting that heat is causing the ground fault to trip, although I guess that might be possible, but rater I suspect that heat is causing a ground fault that trips the GFI. Metal expands and if there is a close fault, the metal expanding could bridge the gap.