I’m trying to install a wall outlet where 3 Romex cables meet and are twisted together. Which goes where?

Question

I’m trying to install an outlet in this junction box I found hidden behind a smoke detector. Inside is what looks like 3 70’s era Romex cables all twisted together by color. (3 blacks 3 whites and the grounds have a weird clamp holding them together.)

There is a light switch directly below this, which is where I think Romex Green probably goes to.

Can someone tell me how I’d wire an outlet with a setup like this?

Should I pull this metal thing off that’s holding all the grounds together?

Should I try and pigtail from each twisted connection to the outlet?

Answer 1

If everything worked correctly before you disconnected everything, then hook your blacks together with an additional 6" piece of black wire. Do the same to the white wires using a 6" piece of white wire. Remove that clamp from the grounds and wire nut then together with a 6" bare or insulated green wire Now take the black pigtail and connect it to either 4 or 5 in your picture. Connect the white pigtail to either the 1 or 2 in your picture. Connect the ground pigtail to 3. Your box fill will be OK with either #14 AWG or #12 AWG.

Oh, and you get a gold star for taking a picture before you disconnected everything.

Answer 2

Method 1. Get a nicer "spec grade" receptacle that supports "screw-and-clamp" back-wiring. These take 2 wires under each screw. Put black on brass and white on silver. Done.

Method 2: What JACK said.

Regardless, the ground MUST be wired and must be pigtailed. That crimp will need to be broken open and a bare pigtail wire added to it. You can use any of a variety of methods to join 4 wires. You cannot use the receptacle as a splice, the ground must remain continuous even if the recep were to be removed!

Also, if the outlet will be in a kitchen, bathroom or laundry room, or if the circuit serves any of these, there are some complicated Code issues with that. Kitchen recep circuits can serve only that kitchen, laundry room recep circuits can serve only that laundry room, and bathroom, only bathrooms but it's complicated.