A common misconception when doing receptacle wiring is that, when you daisy-chain them in a circuit, you're wiring them in series. You're actually wiring them in parallel, and that's a whole different thing. Each device in a parallel circuit receives electricity independently of the others, so if one of them fails, the others stay on. Compare that to a cheap string of Christmas lights, which are usually wired in series. One bulb burns out and the whole string goes off. Virtually all devices in residential circuits – except for switches – are wired in parallel.
It would be against code to wire receptacles in series, and there's no good reason to do it anyway. The total voltage in a series circuit equals the sum of the voltage drops, which means if you have something plugged into each of the receptacles, the voltage of the series outlet at the end would be too low to do anything useful. In a parallel circuit, the voltage across each component is the same. It's possible to overload a parallel circuit, but if you do, all the devices experience the same voltage drop. Before the drop becomes significant, the circuit breaker trips because of the large current draw.
Procedure for Wiring an Outlet
A standard electrical outlet has two brass terminal screws, two chrome ones and a single ground terminal, which is green. When you wire a single outlet to a live circuit cable, you connect the black wire to one of the brass screws – usually the top one, but it doesn't matter – and the white wire to one of the chrome screws. Again, it doesn't matter which chrome screw you choose, but the convention is to choose the one opposite the brass screw to which you attach the black wire. This leaves the other set of terminals free for daisy-chaining. The ground wire gets connected to the ground screw.
To daisy-chain a receptacle onto one that already has power, you attach the black and white wires to the remaining pair of terminals, black to brass and white to chrome. You then twist or crimp the ground wires and attach one of them to the ground screw. The terminals in a conventional outlet are connected, so there's no need for pigtails to create parallel connections. The internal connections on outlets guarantee that power will be split between the receptacle connected to the live circuit and the ones that come after it in the circuit.
The Exceptions to the Rule
GFCI and AFCI outlets are exceptions to this wiring rule. They're designed to trip when they detect a ground fault or current anomaly, and when they do, they cut power to all other devices connected to them. To get the protection these devices offer, you have to wire them correctly.
These outlets have a pair of LINE terminals and a pair of LOAD terminals. The terminals are clearly marked, and the LOAD terminals are usually covered with tape when you unpack the outlet. The black circuit wire goes on the brass LINE terminal, and the white wire goes on the chrome LINE terminal. The outgoing black and white wires must be connected to the LOAD terminals. The ground wires go on the ground terminal, just as they do for a conventional outlet.
Wiring a Switch in Series
Because the purpose of a switch is to interrupt the hot leg of the circuit when it's off, it has to be wired in series, and for this reason, it has only brass terminals (and a ground). You attach the hot wire from power to one of the brass terminals and the hot wire going to the light fixture to the other brass terminal, then you connect the ground wires to the ground terminal, as usual. You then twist the white wires together and cap them. This allows electricity to pass through the switch to the light fixture and return directly to the panel, bypassing the switch on the return path.
If you wanted to ignore code and wire your outlets in series, the procedure would be the same. Connect the black wires to the brass terminals on the outlet you're wiring, connect the ground wires to the ground terminal, then twist the white wires together and cap them. Follow this procedure for all but the last outlet in the circuit. On that outlet, connect the white wire to one of the chrome terminals to provide a return path directly back to the panel, bypassing all the other outlets.
Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker.com.