House is an older home from the 1890's, the wiring has all been replaced over the years, new panels, all that, but often decades apart so there are many generations of electrical all hooked together, but no knob and tube and no 2-wire.

Here's the setup: I put a GFCI in my basement where a normal plug was to plug in heat cord for some pipes. GFCI works properly, both the test button and a separate plug tester all show proper operation. The breaker is a normal 20A with no AFCI.

This GFCI is at the end of a wire that has a few other things on the circuit, namely some things that go into a 3-season room. I connected a new wire to the load screws, and attached the ground into the same ground screw, so this plug has 2 ground wires on the same ground screw.

I double checked the hot/neutral, it is for sure on the correct screws, and ran it down to my new location which is a joist by the boiler where I want to plug in some new things.

I wired the new plug and used the line screws, double checked again. I turned the breaker back on and the GFCI works properly and tests properly, but the new AFCI/GFCI combo trips instantly.

I took it apart and checked all the wiring, it is all correct as far as I can see. The GFCI appears to be working, the little green light is on and the plug tester has the correct lights, and the test buttons both trip it.

The new AFCI/GFCI combo instantly trips from the moment I flipped the breaker back on.

So, what is my next diagnostic step? The only thing I can think of is that somewhere in the circuit there is something that triggers the AFCI portion, but that is pure speculation. The house is 130 years old, and so all of the electrical modernizations over the years could have meant that somewhere on this circuit there is something the AFCI doesn't like, but I have no idea how I'd determine that.

What's next? Now that I know there's something wrong I will need to figure out how to both fix anything causing the trip, and also get myself a working plug.

  • 1
    An AFCI receptacle should not trigger on anything but a problem on it's load side or plugged into it. But, simple check is to wire that receptacle to a very simple circuit with no room for error and nothing odd upstream of it. If it operates correctly, you go back to hunting your snarks. If it trips instantly anyway, might be it's got a problem.
    – Ecnerwal
    Commented Mar 10, 2023 at 2:52
  • @HelloSean to confirm, you have a GFCI run off the load terminals of another GFCI?
    – mmathis
    Commented Mar 10, 2023 at 13:49
  • The GFCI upstream has electricing coming in and hooked to the line terminals - the yellow sticker was still on the load when I added the new run from it. The new wire connects to the load terminals where that yellow safety sticker was, and then connects to tthe AFCI/GFCI combo plug (also Leviton) on its line terminals, with the yellow sticker still on it. I believe that confirms what you're asking.
    – HelloSean
    Commented Mar 10, 2023 at 16:40
  • I just traced the whole circuit, that breaker goes to a jbox which then feeds a new outdoor GFCI, this new series of plugs this post is about, and then a metal-clad run to a single plug out in the three-season room that is old enough that it would use the metal-clad. It does not have a ground wire, but the outlet tests properly and is grounded against the metal-cladding. That plug can be decommissioned for now for testing. The entire run could be disabled for testing in fact, none of those plugs are essential or even powering anything.
    – HelloSean
    Commented Mar 10, 2023 at 17:01

1 Answer 1


I connected a new wire to the load screws, and attached the ground into the same ground screw, so this plug has 2 ground wires on the same ground screw

Not allowed to do that. The screw isn't designed for 2 wires. Also removing the device would sever the ground to the downline. Ground is always pigtailed for that reason.

So, what is my next diagnostic step?

First, unplug everything from the AFCI and see if the fault clears (it holds). If it does, it's a plugged-in appliance.

Second, go in there and remove all wires from the LOAD terminals on the AFCI. Then see if it holds. If it does, it's a problem in the downline wiring or appliances. If I understood your description correctly, this AFCI is at the end of a new circuit extension and nothing would be on the Load terminals.

Next, search the installation and see if any screws or wires are touching the box or ground wire when the stuff is pushed back into the box.

Lastly, check the wiring between the outlet and the supply. Because this is an AFCI receptacle (why it is on the end I have no idea), AFCIs have the ability to "hear" arcing on the supply side. So arcing on the supply side can trip them. Even arcing on other circuits has been known to trip them.

  • One thing I didn't mention I want to add: is induction a thing to look for? The new wire runs parallel to a bunch of other wires, all stapled to the joists, the whole house was wired using a removed-chimney chase to get all the wires into the basement, then they run the entire length of the house to the panel. There are normal 12/14g romex, a few higher voltage lines for the oven and dryer, and then an even huger run that connects a panel in the garage. New one does run parallel to these live lines, and then also crosses them perpendicularly at the end to get to the new plug location.
    – HelloSean
    Commented Mar 10, 2023 at 16:43
  • I will use your advice in the comment and hunt more. It is in a metal box, so there could be something touching that, I can test it when it's dangling from the box. There is nothing plugged into it, it won't un-trip, each time I press "reset" I see the red light blink and it clicks and trips. It's going above my boiler so I can mount a camera to it, so I went with the AFCI/GFCI combo thinking that this is a place where there's potential water/steam/other things in nasty colonial basements, so I figured the extra safety was good. Maybe a normal plug is simply the right choice??
    – HelloSean
    Commented Mar 10, 2023 at 17:42
  • @HelloSean induction (or capacitive coupling) is not going to trip an AFCI. If it's tripping due to arcing on another circuit, it will "hear" that arcing condutively not inductively. So it may be exactly that, a canary in a coal mine. Commented Mar 10, 2023 at 19:32
  • Okay, and so since I can trace the jbox it comes out of all the way to the panel, I should be able to disconnect things and isolate it down to specific branches... presuming that it can't also "hear" something on entire other circuit? I have this same combo plug in other locations that work, and also 5 or 6 AFCI breakers in the panel that all work fine, so I am hoping that it is just something on this specific circuit, and the old BX armored cable is the most likely suspect. Unless it can hear literally anything in the house, which I can't fathom how I'd hunt it down :)
    – HelloSean
    Commented Mar 10, 2023 at 20:40
  • 1
    Everything appears good now. Screws are secure and wires seems to be in the box and not causing the gremlin. Not sure what the key was exactly, but one of them solved it. Good to know for next time.
    – HelloSean
    Commented Mar 12, 2023 at 20:50

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