[logan]

I have an outdoor lighting and receptacle system (120v, 20 amps) that has developed a bug that I can’t figure out. Sorry for the long post - but it's a complicated system.

Everything worked fine for the first 1-1/2 years but now the circuit breaker flips after lights have been on for anywhere from 20 minutes to 48 hours – usually 2-3 hours. I can’t figure out what the trigger might be.

12/2 Romex runs from the box in the basement (20 amp breaker) through PVC conduit to a junction box located on the back brick wall of the patio. There’s a single-pole switch on the inside, just prior to the outside box. On the outside, there’s a receptacle box with 2 GFCI outlets 12” above the main junction. Out of the bottom of the main junction box is PVC conduit running under a stone patio to T box. Run is about 12” below the foundation of the patio and then rises to the ground at the edge of the patio, where there are two T boxes on either side of the yard.

Two lines go down each side of the 15’ wide rectangular yard (row house in a city). Conduit runs along the ground or slightly below. At intervals of about 6 feet, there’s a T that feeds a 20-amp GFCI outlet (12” off ground), and above that, an outdoor-rated wall sconce. There are 6 GFCI outlet-and-light pairs on each side of the yard – 12 total. Yard is 35 feet deep.

Everything is in outdoor-rated gray PVC, except for sconces – these fixtures have a hollow metal base which is mounted vertically on wood planks. Conduit runs up a groove in back of the plank to a hole through the center of the plank, through which is fed the 12/2. The 12/2 is connected to the lamp wires (which are standard lamp cord). Planks are sealed with glue to wood fence posts and screwed in; no water access.

GFCI outlets have plastic covers. Backyard does not flood, nor is there ever standing water.

The maximum total wattage of the lights is 900. There are 8 additional spots on the ground, on cords that plug into the GFCI outlets. Maximum total wattage for these is 1200. Since the problem started, I’ve unplugged all of the spots and there’s no change in the behavior – the wall lights will stay on for 20 minutes to 2-3 hours then the breaker flips. (When the spots are plugged in, the GFCIs sometimes flip when there’s lots of rain – but that only affects the outlet and the light above it – rest of system stays on.)

I’ve tried to isolate the problem – when I disconnect either one of the first above-ground boxes on each side, problem persists. When I disconnect both of the boxes, breaker stays on for a week or more but eventually pops. When I reconnect one or both, problem returns. I have not gone through the other 5 junctions on each side. When the inside switch is off, the breaker stays on indefinitely.

Thanks for any help you can provide.

[tkrussell]

The wire at the breaker may be loose in the lug connector on the breaker. If this is loose, with the load you have, the connection will get hot, and this heat will migrate inside the breaker and trip it, for no apparent reason. Or the breaker may be loose as it is pkugged into the panel. You may need to unplug he breaker to inspect it, this will also creat heat that can trip the breaker.

Sounds like you checked everything else, so my bet is the breaker connection is loose, or the breaker is defective. After checking the breaker connections, and if this is OK, then try swapping this wire to another breaker, let it run for a few days to see if which one trips.

[logan]

Yes, this seems to be right. Definitely seems like something is getting hot and shifting, causing the breaker to flip off. Can't get into the panel tonight, but will try this and report back.

My sense has been that something in the backyard was heating up - the only thing I could think of is that a splice was coming loose as it got warm, but now that it's really cold outside and it still goes off within minutes, it makes sense that it's back at the breaker.

logan