Presently using them to light XMAS lights on one of the citrus trees. IIRC, each string is about 250W. With ~700W on the circuit, turning the breaker ON (i.e., using it as a switch -- instead of plugging/unplugging the load) causes it to immediately trip. Repeating the action in short order appears to get it to latch and remain latched (ON), indefinitely.
OK, so the surge when all the lamps are cold can increase the inrush current -- on the short term -- to levels that probably exceed the 20A limit of the breaker.
OTOH, in years past, I've run the circuit at close to its capacity (~10 strings) without this problem.
I've changed breakers (swapped with one feeding another circuit) and the problem persists.
[There are no leakage paths in the wiring OUTSIDE]
This suggests something in the wiring/fixtures. I'll start isolating outlets, tomorrow (dark here, now). Perhaps some insect (leaf cutter?) has opted to nest in one of the receptacles.
Anything else I should explore?