I want to install a receptacle into an existing junction box (photo below). Within the box, there are three neutrals (white) and five hot (two black, two blue, and a red). All of the wires have wire nuts (two wires per nut) with one end going down to the basement and one end continuing through the box up to the next floor. I plan to pick on of the blacks to tie into (probably via pig tail) but I don't know which white to connect to. Does it matter since the are all going to the same place (neutral bus bar)? Seems like it might since it seems like you don't want a single circuit coming back to the panel through two different neutrals.

The home is in the State of Illinois

Junction Box

2 Answers 2


Box Fill

Box fill might be an issue. There are 8 current carrying conductors, if they are 14 AWG, that's 16 cubic inches (18 if 12 AWG). Plus another 4 cubic inches for the receptacle (4.5 for #12). And another 2 cubic inches, if there are grounds (2.25 for #12).

Equipment Ground

If there aren't any grounding conductors, you'll either have to install a 2 prong receptacle or a GFCI receptacle with a "No Equipment Ground" label.

What's What

You'll also have to figure out where all the wires are coming from, and where they are going. You can't just tap circuits all Willy Nilly, you have know what else is on them.

Which Neutral

As for which neutral to use, you should defiantly use the grounded (neutral) conductor from the same circuit as the ungrounded (hot) conductor you're using. You could end up overloading a neutral, or other problems if the circuits are out of phase.

  • Understood regarding the box. I was going to get a box extender to make room for the receptacle. Upstairs there are just receptacles, lights, ceiling fans - no major current draws except gas furnace & I won't be using that circuit.
    – user18891
    Dec 29, 2013 at 20:43

You'll want to turn off all the breakers at the main, then turn them on one by one until you can count how many circuits feed this point.

It's possible there's just one feed, and the other two neutrals are loads. It's possible the feed is a 220V red/black/white coming from the bottom conduit (can't tell from the picture).

  • Thanks for your reply. I doubt this is a 220v circuit. There is nothing on the floor above except lights, ceiling fans, receptacles, and a gas furnace. However, there are two rooms & bathroom so makes sense there would be multiple circuits.
    – user18891
    Dec 29, 2013 at 20:30

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