First off, I apologize for my ignorance; I'm new at this. Does electrical wire (12 gauge for example), come as a single wire? For example, if I'm installing a 20A outlet 40 feet away from the breaker, do I need 40 or 80 feet of 12 gauge wire?It is my understanding that each outlet needs a (+) and (-) wire, as well as a grounding wire. Is this correct?Thanks for your help!
The most common wiring system these days is 'Romex' cable which is a plastic jacketed assembly of two current carrying insulated wires and a bare ground. There is a lot that you'd need to know about how that cable may be routed through a structure, and how it needs to be anchored to the structure and terminated at it's ends to even come up with the actual length of it you will need, let alone make a safe installation though. There are good home wiring manuals available, and I strongly suggest that you don't even touch any power wiring without reading one.
I would strongly suggest not doing your own wiring as your lack of knowledge can cause serious issues. 12/2 is a black wire (hot), a white wire (ground) and a bare copper wire (ground). 12/3 contains another wire for doing things like having a light with two switches. 12 gauge is heavier wire and is used in 12 amp circuits. 14 gauge is a bit lighter and is used in 15 amp circuits (mainly lighting). Do not ever use 14 gauge on a 20 amp circuit as the wire will melt before the circuit breaker disconnects. You can, however, use 12 gauge on a 15 amp circuit even though you are just wasting money. There is also a difference in the outlets between 12 and 14 gauges but that is a different lesson.
You would normally hire a professional to do a job you don't know how to do, read a book about it, watch how it's done, ask a few questions and then try a simple job under supervision of someone with more experience. A 20A receptacle would normally need a cable marked 12/2 with ground, type NM (if allowed non-metallic) or type AC (armored). You would need enough to get from the closest existing branch circuit to the location of the new outlet, including going around corners and up inside or down inside walls, ceilings and floors, to hide most of your wiring. Yes, a receptacle would need to be connected to a hot, a neutral and a grounding conductor, for proper installation under most US electrical codes, although there are exceptions.
If there's netural already in the box ,then you just need a single hot wire 40 feet tall to the out let ,but if there's no neutral and ground ,then you need to install a neutral and ground from closer junction box or electrical box to order of having function electrical box . This is not necessarily for neutral to be directly from the main electrical box ,but power source must be directly from the breaker to the electrical box and for 20 Amp with that distance you should use the wire gauge #10 . If wiring is in the conduit pipe ,then you will see two wires white and black ,which you jusy will replace the black wire and if there be short between the hot and neutral ,then you must replace both wires as long as they are .
You would need over 80 feet of wire. In fact you would need over 120 feet of wire. Bends and non-direct routing will take up some of the distance. You need three conductors: one hot (usually black, blue or red in the US), one neutral (white in the US) and a ground (either green or bare). Individual wires MUST be run in conduit, but if the entire run is in a sheltered area you may be able to use nonmetallic cable, for instance Romex. This is the white or yellow flattish cable you see that has two wires inside it plus a grounding conductor. In such instances the ground is usually bare. Under certain conditions you can also use flexible armored cable (looks a bit like a flex lamp neck). I'm not wild about the stuff but it has its uses. You sound pretty new to the whole electrical trade and I strongly advise you to proceed cautiously after reading up on the subject. If in doubt, call a pro. It won't be cheap, but it's cheaper than rebuilding your house after it burns down, or paying funeral costs.
