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
Best Answer
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.