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I have five romex wires going into a single outlet box. However things are a bit messy and I don’t understand the wiring scheme or any scenarios that this would account for. So here is the layout

4 of the romex wires are setup exactly how I would assume. They are wire nutted together neutrals(white) together, hot (black) together, And then the grounds. Here is where it gets funky. The fifth romex cable has the black wire going to neutral side of the outlet and the white neutral wire is twisted with the other four black wires. So then there is a black pigtail going from the four white wires to the hot side of the outlet.

Any ideas?

Lastly receptacle says 15a on it but breaker says 20a so even that is strange as I would think the outlet would Burn up first.

I also tested this with a outlet tester and it came back as correctly wired. House is built in 83.

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There is a switch somewhere that controls that outlet. Additionally, the hot and neutral are reversed, or the switch controls the neutral.

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  • if the hot and neutral are reversed wouldnt the outlet tester not show correct? Also, doesn’t a switch usually control the hot wire, what wpuld controlling the neutral do?
    – Qiuzman
    Commented Jun 29, 2021 at 20:14
  • An outlet tester is not smart enough to detect all types of wiring faults, and there are multiple ways to cause a hot/neutral reversal. And yes, the switch normally controls the hot wire. Switching the neutral has a similar effect (the appliance plugged in to the outlet stops working) but leaves it in a potentially dangerous position of still being able to shock someone who thinks the electricity is correctly turned off.
    – longneck
    Commented Jun 30, 2021 at 4:50
  • If that’s the case why would the outlet tester have a light code for when the hot and neutral are switched?
    – Qiuzman
    Commented Jun 30, 2021 at 15:48
  • @IrishRedneck They don't. Outlet testers have 3 neon lights connected between the 3 pins. Then, they need to figure out something to say for every combination of lights, because they think people wouldn't like their product if they said nothing. This is act of creative copy-writing, and the advice is tuned for the kinds of problems that crop up in new-construction wiring (i.e. checking the work of the apprentice) NOT what happens to old wiring. You can follow those legends if you really want to, but prepare to be led on a snipe hunt.
    – Harper - Reinstate Monica
    Commented Jun 30, 2021 at 17:04
  • I’m just paying to have an electrician finish / potentially fix this. Ughh how does adding a single exterior outlet turn into this scenario ha. My luck.
    – Qiuzman
    Commented Jun 30, 2021 at 17:45
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15A receptacles are internally rated for 20A pass-through. That's a UL requirement. That is because 15A receptacles are allowed on 20A circuit due to an NEC rule/exception.

Receptacles (even GFCI) do not provide any sort of circuit breaker or fusing. If someone fed a 30A travel trailer outlet through a 15A GFCI receptacle, the GFCI will try its best to carry the current, and won't trip... it will only complain by catching on fire lol.

However I am more concerned with the number of Romex cables inside that box. Most junction boxes are only good for 2-3 cables.

You compute it by counting the wires.

  • Each hot or neutral wire coming in counts as 1 (so 2 wires per Romex generally).
  • Grounds, are a "4 for the price of 1" sale, so I count 2 grounds that we have to "pay for".
  • Receptacles count as 2 wires.

So I get 14 wires presently, and your plans will make it 16.

20A breaker means #12 wires. Those take 2.25 (2-1/4) cubic inches per "wire". So we are at 31.5 cubic inches presently, and your plan will make 36 cubic inches.

Now look at the writing in the back of the box, I bet you have about 18 cubic inches in there, maybe 22 tops.

That's why your box is overfull.

I would install a 4x4" box extension (1-1/2" deep, 21 cubic inches) and a domed cover (7 cubic inches) for 1 receptacle. It'll stick out from the wall, but it'll take care of your space problem.

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  • That’s good to know I can use my 15amp outlets on the 20amp circuit. Why do there exist 20amp outlets then if 15amp are rated for 20amp?
    – Qiuzman
    Commented Jun 29, 2021 at 20:15
  • @IrishRedneck because some appliances really do need 20A. They have the rotated neutral pin, and cannot fit in a 15A socket.
    – Harper - Reinstate Monica
    Commented Jun 29, 2021 at 20:28
  • I have actually decided to investigate this myself. I took out the old box and added a double box since you are right the volume was overfilled. I ran the new wire and updated post above. This wiring scheme is strange. I know what it was before so I am fine to go back to the old way but I need to understand this first.
    – Qiuzman
    Commented Jun 30, 2021 at 16:39
  • The black wire could just be a pigtail from the neutral bundle to the receptacle. It's sloppy not to use a white pigtail, but most inspectors would let it slide.
    – Harper - Reinstate Monica
    Commented Jun 30, 2021 at 17:32
  • First I’ve learned non contact tester are not reliable enough to know if there is current. I used a multimeter and there is electric coming from only one romex and it’s a black wire ! So to understand if the outlet is reversed by accident is there a way to test?
    – Qiuzman
    Commented Jun 30, 2021 at 18:11

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