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I'm trying to ID the first outlet in a circuit. I've done this procedure successfully before, to install a GFCI, but this time around, I'm utterly confused. I've removed the wiring from three different outlets (separately, one at a time), all on the same breaker, but each time I had one disconnected, all the other outlets on the circuit continued to work. How can this be? Is this some novel wiring configuration? Each box houses a duplex and has two copper wires coming into it: white & black. The white wire is attached to one side of the receptacle and the black wire is attached to the opposite side.

This pertains to my upper-level bedroom circuit, but my kitchen circuit is (apparently) a multi wire branch circuit (I barely know what that means). I had previously suspected that perhaps my upstairs confusion was for the same reason (MWBC), but with only two wires in each box, it doesn't make sense to me. Is my upstairs just wired in a 'star' configuration: where all the outlets are fed individually from a single feeder line or junction box?

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  • Adding some more detail: my question pertains to my upper-level bedroom circuit, but my kitchen circuit is (apparently) a multi wire branch circuit (I barely know what that means). I suspected perhaps my upstairs confusion was for the same reason, but with only two wires in each box, it doesn't seem likely. Am I just looking at a 'star' wiring format: where all the outlets are fed individually from a single feeder line or junction box? – Matt Goodman Apr 26 '20 at 23:31
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    I think key is Each box houses a duplex with two wires in it (white & black). Please confirm that you have (ignoring bare/green grounds) just two WIRES in each box, not two CABLES with two wires each. If that is the case (just 2 wires, 1 white, 1 black) then yes, you have a star configuration, at least for those outlets. – manassehkatz-Moving 2 Codidact Apr 27 '20 at 2:53
  • @MattGoodman please edit additional information into your question, rather than tagging it onto the comments. – brhans Apr 27 '20 at 12:07
  • How do the wires enter the box? Are they coming in on a cable sheath, or are they coming in a conduit pipe (where the wires can flop around and move back and forth 1/4" or so)? – Harper - Reinstate Monica Apr 27 '20 at 22:51
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OK I think I get it. Harper is getting up to speed.

So you are looking to competently use the GFCI LOAD terminals on a GFCI recep to protect the downline. You want that because GFCI receps are cheaper by half than GFCI breakers, and you don't have to open up the panel.

This smells like metal conduit.

The lack of ground wire makes me wonder if you actually have metal boxes and metal conduit. I would look closely to see if the wires are disappearing into a pipe (about pinky-sized). Look for a metal thread coming in and a metal "jam nut". If that's really metal conduit, metal conduit is a valid ground path. It may be worth revisiting the question of why you're installing GFCI in the first place - e.g. if it's to allow 3-prong receptacles where no grounds exist, that is altogether unnecessary! A 3-lamp tester will confirm that.

Assuming you still want to proceed...

If only 2 wires enter the box, then either it's a dedicated circuit or just as you say, it's wired in a star or tree topology.

It might not just be in boxes on this circuit. It could also be in

  • blank boxes (Code requires they remain accessible, but idiots do exist).
  • Boxes of totally unrelated circuits, with careful separation of neutrals.
  • Boxes of this same multi-wire branch circuit if it is one. (you'll have to open up the panel to see).

The good news is, if it's conduit, you can add more wires to conduit. For instance you pick any appropriate receptacle, put 2 more wires right back up the pipe (I prefer purple and gray myself for GFCI protected wiring) back to the hub, and then use the hub to spread GFCI protection to the other outlets.

All MWBC breakers, two (or three in NYC) should be handle-tied, so either get manufacturer approved handle ties, or get a 2-pole (3 in NYC) breaker. Breakers must match the panel, or be UL-Classified for the panel (Eaton CL basically).



Other scenarios that can appear with 2 cables (4 wires):

To me this is normal:

Supply wire comes in, is wirenutted to onward power and a pigtail to the receptacle. 1 wire lands on the receptacle. (repeated for hot and neutral).

What you are thinking as normal is:

Receptacle has 2 screws on it, and those are connected to each other and to the receptacle itself, thus allowing the recep to also act as a splice block. Supply wire on one screw, onward on the other screw.

Both ways are correct.

However, if you're a novice installing GFCI receps, and your goal is to use the LOAD terminals to protect the downline, then the second method is more obvious.

However, MWBCs really interfere with that.

In a multi-wire branch circuit (MWBC), the neutral is shared between the two hots. Where the neutral is shared, it must be pigtailed.

So pigtailing, especially when it's just neutral, is a "canary in the coal mine" for a MWBC. You need to go evaluate the circuit to see if you have a MWBC.

If you do, then you cannot use the GFCI LOAD feature to protect the downline. You must use individual GFCI receptacles at any point where the neutral is shared.

Now if you're doing the math and going "That'll take 5 GFCI receps, I can buy a breaker for that" - you are exactly correct. The simplest way to GFCI-protect a MWBC is a 2-pole GFCI breaker.

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  • This helps my understanding some, but as far as I can see, there is no "onward" wire. Only two copper wires coming into each box: the white wire is attached to one side of the receptacle and the black wire is attached to the opposite side. No pigtails anywhere, no other wires (except bare ground/green to the metal box, in some cases). – Matt Goodman Apr 27 '20 at 18:13
  • @MattGoodman Alright, I made an edit pass. I have to say this smells like a conduit installation. – Harper - Reinstate Monica Apr 27 '20 at 23:48
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You are going to have to identify every outlet on the circuit you want to place the GFCI on. Just turn off the breaker and test with anything, A simple lamp will do. Most likely you'll find the head of circuit for your GFCI location. EDIT: The wires in the outlet boxes aren't pig tailed are they? You should have 2 blacks, 2 whites and grounds connected to each outlet. If pig tailed, that would explain why other outlets aren't affected.

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  • I understand the methodology of testing each outlet as you've described above and, in fact, this is the methodology I've been employing, but my issue is that none of the outlets appear to be 'upstream' of any of the other outlets...that's what I'm asking about and trying to understand. What kind of configuration would cause this? Is it typical, standard, or vestige of old wiring code that's no longer used? In answer to your question about pigtails: no, there are none. I've edited my question to make it more clear. – Matt Goodman Apr 27 '20 at 18:08

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