Wiring – Why does the GFCI receptacle trip when anything is plugged in

gfciwiring

My house was built in 1994. The garage is fed from one 20amp circuit wired to the lights first, then a GFCI, then a couple regular outlets. This has worked fine for me for 19+ years.

We had a storm Friday morning, after which the GFCI now trips when anything is turned on (even a power-strip with lighted switch). Garage lights still work (as expected since they are ahead of the GFCI). With the CB off, I put my meter on the receptacles to look for a short, but found none. With CB back on, all receptacles have 120vac available, but the second something that draws even the smallest amount of current is plugged in, the GFCI trips.

I replaced the GFCI with a brand new one, but still have the same problem. I pulled the GFCI out of the wall and put my meter on the screw terminal. Both line and load have 120vac when reset. If I press the test button, the line side drops to 32vac and the load side to 10vac. The garage lights still work fine at full intensity, so the line voltage on the garage circuit isn't dropping.

The only possible explanation I can come up with is that a broken wire (high winds caused the garage structure to shift?) is still making some contact to pass 120vac at no current, but the poor connection is causing the voltage drop with any load and causes the GFCI to trip. The GFCI has a tiny LED that comes on when tripped (off when reset) which must be creating the small current draw.

Anybody else have any thoughts?

I don't relish the though of opening the walls in the garage to run new wire. Perhaps I'll temp one with an extension cord to prove the solution electrically first.

Best Answer

It certainly seems like you have a ground fault somewhere. Is it possible there is water damage anywhere inside the garage?

Since you've already replaced the GFCI, I think it's safe to assume it's working properly and is tripping as it's designed to. That means somewhere current from the hot or neutral wires is leaking to the ground wire or somewhere else. (I'm guessing it's a neutral -> ground short, since it only happens when you try to use an appliance. A hot -> ground short should trip the GFCI as soon as the power comes on.)

Here are the things I would try:

  • Does the tripping happen at the GFCI, or just the downstream outlets? If it's easy to tell which order the receptacles are wired in, start by plugging something in to the first one downstream of the GFCI. Does that trip it? If so, the short is probably between that outlet and the GFCI. If it doesn't trip, move to the next outlet and see if that trips, etc.
  • Take the cover off all the outlets and inspect them. Look for any signs of moisture, or a loose wire nut, or a conductor touching the side of the box.
  • If you don't see anything suspicious, start pulling the outlets out and rewiring them. Disconnect them all and start adding them back one by one.
  • If you still haven't found the issue, it's possible the wiring inside the wall got damaged somehow. Possibly a combination of mice chewing on the wires and moisture from the storm? If you've reconnected the wiring to the outlets one by one, starting with the closets, you should at least be able to tell which section of wall the defect is likely to be in.

Other notes:

  • I'm not sure if the continuity tester will help much, the problem is a short not an open circuit. Especially if the problem is caused by a neutral / ground short, those are always going to test as continuous since they connect at the main breaker box.
  • I wouldn't worry too much about the voltage readings you got with the GFCI tripped, open circuits can sometimes have small but non-zero voltage readings.
Related Topic