In my dorm room closet, there is a junction box with a blank plate (no outlet). Inside there are three wirenuts (hot, neutral, ground).
I know it is generally unsafe to do any work on a live circuit, so I will see if I can set the circuit breaker. If I cannot, is there a safe(ish) way to perform this operation?
Theoretically you could wire an outlet with live power by not grounding yourself, keeping the wires separate, using gloves, etc.
But the chances are so great that you could either electrocute yourself or start a fire that it's inappropriate for anyone here to suggest it, and foolhardy for anyone to attempt it.
Always turn the power off first, test your wiring to ensure it is powered off, and even then treat it as if it could be live. And finally, take Shirlock's advice, don't wire an outlet in a closet.
There is a reason they put a blank over that box. They do not normally put outlets in a closet, as cords plugged into them tend to get buried in junk if close to the floor or a shelf, creating a potential overheating and fire hazard. Under no circumstances should you attempt to wire an outlet to these wires hot. It is never a good idea, even if you knew what you were doing. SO DON'T!!!!
In a closet, that is an enroute junction box, which is there for accessibility (perhaps because the building is wired in conduit and they don't want too many bends between accessible points).
Because it's enroute, you have a special problem: you will be breaking splices that have current flowing through them. For instance when you break open the neutral wire-nut to add your neutral wire, the current flowing through them will arc impressively, and when you get them apart, now the supply neutral will be near ground, but the load neutral will be pulled up to hot potential by the current trying to return. All downstream neutrals on that circuit will also be at hot potential, if anyone is bootlegging ground, you just killed them. It's really hard to wire-nut wires that are actively arcing.
It's not intended to have a receptacle there, because receptacles in closets are a bad idea, as the cords plugged into them will get covered in clothing and potentially overheat.
If you really, really want to do this, talk to building management with the following proposal: run surface conduit (wiremold) from the junction, to a correct switch location for a closet light, then up to the ceiling for the closet light. Say you want to use a plug-in light you already own and ask them to provison a switched receptacle up there. Why? Because the ceiling is the only safe place for a receptacle in a closet, and putting a receptacle on a ceiling only makes sense if it's for a plug-in lamp.
You will probably have to spend a bit of money on this, it might help if with permission and inspection you did the fitting of the surface conduit yourself, properly. Though union rules may disallow that.
[ Caution: community members have reported that this advice is potentially dangerious ]
put a light socket with a outlet in that box . then if you decide to plug something up, plug it in then run the plug's cord along a safe passageway, then secure it there with glue or something else that wont damage the cord but will keep it in one place . its safe ways to have power in the closet . but when dealing with live circuits, use rubber insulated gloves, insulated tools, insulated fiber glass ladder, etc. I heard its good to even use a thick rubber matt to keep you off ground.
