I was attempting to wire in a new GFCI receptacle on the exterior of my house. i ran a new 3wire 12 gauge BX cable and wired it onto an existing junction box in the basement. The junction box is attached to a switch which leads to another junction box then to the circuit breaker. The other junction box goes to a number of light fixtures in the basement.

When I flipped the breaker on then flipped the switch on it tripped the breaker. I thought I saw an arc travel between the box that the switch is on and the ground wire on the BX cable.

I'm pretty certain I wired the GFCI correctly i've wired a bunch before. I'm trying to determine what the most likely cause of the issue is and how to troubleshoot it. I'm thinking it might be the switch it's self ( since it's an old switch ) but i'm also wondering if it could have something to so with the GFCI being in parallel to all of the lights. Any help would be great.

  • 3
    Please upload pictures showing the wiring (don't disconnect anything - we need to see how it is now) of the GFCI, the switch and any other junction boxes that you worked on as part of this project. Nov 7, 2022 at 15:18
  • 2
    A hot wire/screw is too close or touching a box/bare ground wire. Seeing the arc, you probably found the first place/device to check. I assuming that you are tripping the breaker and not the GFCI.
    – crip659
    Nov 7, 2022 at 15:18


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