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I have one circuit dedicated to outside deck outlets, and a shed in the back of the property. I use a GFCI breaker for this circuit. The wire connected to the breaker in the panel runs to a junction box, where it connects to a wire leading out to the deck and another leading to the shed. This has been in place for many years with no issues. The breaker tripped last night, and wouldn't reset. The only items plugged in were a couple low voltage transformers, and a timer for low voltage deck lights. I unplugged each item, and the breaker still trips.

Now the weird part. When I separate the wires in the junction box, and connect the power wire from the breaker to either the deck or shed wire, the breaker does not trip. If I reconnect the power to both deck and shed wires, the breaker trips. Any ideas what would be causing this?

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    When you say "connect the power wire", do you mean "hot wire" or "hot and neutral wires"? Is ground via metal conduit or a separate ground wire? Apr 2 at 22:33
  • Hot wire. I did not disconnect the neutral wires. There is a separate ground wire.
    – Doug Morse
    Apr 3 at 23:06

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Well, let's stop and think about what a GFCI does.

GFCI stands for Ground Fault Circuit Interruptor. The "circuit interruptor" part you've already met. "Ground Fault" means a case when electricity goes where it should not (fault), and presumably to ground (not necessarily the ground wire). This is concerning because it could be getting there via a human or pet, shocking them to death or starting mischief.

A GFCI is comparing the current on the hot wire to the current on the neutral wire. In an electrical circuit, currents are supposed to be equal on hot and neutral. If they're not equal, that's proof that electricity is going on some third path, e.g. to ground.

That is what is tripping your GFCI. Electricity is supposed to stay only on hot and neutral, and it's going somewhere else.

Since you claim you unplugged everything on the circuit, it must be a problem with the wiring in the circuit. 95% of the time, this is in a junction box, and you can open up the junction box and remove the mud wasp condominium and take care of it. The other 5% is dominated by people who use NM "Romex" cable outdoors or underground where it doesn't belong; the insulation rots.

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  • The junction box is inside the house, so no issue there. The wiring to the shed and deck are rated for direct burial, so they should be good. The problem breaker was a combo unit, providing Arc Fault and Ground Fault protection. My understanding is that outside outlets do not require Arc Fault protection. Since I had tried everything I could think of, I decided to purchase a new GFCI breaker only. I’ve had no problems since installing the new breaker. Thanks for your comments
    – Doug Morse
    Apr 3 at 23:09

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