Look in places where GFCI's are required (unfinished basements, garages, outdoor receptacles). It also could be in the electrical panel itself, built into the circuit breaker.

FOUND! Thanks. This had been making me crazy. I also discovered it took out 2 outlets in a secondary bathroom we never use.

Garage was the location - two GFIs in a double outlet hidden behind some stuff and one of them was the culprit. Kind of strange since it's very very far from the back of the house to this location, but finally figured it out.

It can be amazing where the GFI can be located. There are two options that I like better. One is GFI breakers. We all know where the breaker box is. Where I live now is about six years old, and where required (kitchen, bath, balcony) every outlet is a GFCI. They have come down in price to where I guess they just install them where needed.

Dale

The big reason builders don't use GFCI breakers is they are more expensive than the receptacle type. You'll only find a lot of these goofy mystery circuit things in older houses. Newer codes bar the bathrooms, laundry rooms, and kitchens from sharing outlets with other places (garages, basements, outside).

I just find it amazing the every bath and kitchen counter outlet is a GFCI. They now have outlets with a USB port built in. We wanted those on the island, but size wise they cannot make it a GFCI also. We would have to make it a circuit protection or gang two outlets at the location.

Our bedrooms have arc protection. What a pain as they can be pretty sensitive.

The only GFCI breaker we have it to the bathtub.
DaleP

You don't need a GFCI receptacle at each location on the countertop, they just all need to be PROTECTED by a GFCI. You can daisy chain them off an earlier receptacle in the circuit or use a GFCI breaker.

Depending on when your house was built, you might want to look into replacing the arcfaults with newer ones. The old GE mod 2 arcfaults in my house nuisance tripped a lot, but GE went to mod3 and that solved a lot of the problems.

The one I wanted to add as a USB port was one of the early outlets in the circuit. Too close to the sink not to be a GFCI. I thought about cutting in for a double box, put one GFCI also protecting the USB outlet. Actually, kind of got over it. I am used to the USB adapter plugged in all the time.

I had heard that the newer arc protectors were less sensitive, but have not had a problem lately. They had put an arc protector to the den. Home office did not agree with the arc protector. Since it is a den and not a bedroom (no door, no closet), I just took out the arc protector and put in a normal breaker.

DaleP