Originally posted by: Engineer
For that matter, isn't there two terminals on each side of the recepticle....one for in and one for outgoing connections? I know GFCI's are this way with the exception that the outgoing is controlled by the GFCI circuit, but IIRC, the regular recepticles also have double terminals on each side.
The reason for the two screws on each side of a dual receptacle is NOT to provide a junction connection. It's to allow for conversion to a "Split Duplex" receptacle. In a Split Duplex system you bring in from the breaker box a 3-conductor (plus bare Ground) cable with Black, Red and White. As usual, black is hot, white is neutral, and red is also hot but MUST be from the OTHER hot bus in the breaker panel. At that panel you must use a dual breaker so that tripping it shuts off BOTH hot feeds simultaneously. (Between black and red you have 240 v AC.) At the receptacle, on the hot side, look closely and see that the two parts with screws for the hot leads are connected together with a simple piece of metal you can break away by bending. Leave it on and you have two sockets fed by one hot supply line. But once that is taken off, the two receptacle halves become separate circuits, and the black and red hot leads each go to ONE of those screws. On the Neutral side there is only one common neutral connection, the white lead. It will carry back to the breaker panel the net unbalance current. In the case of plugging in only one load, the white lead will carry back the same current as the hot supply (say, from black). But if you plug a second device into the other (red wire) half of the split duplex receptacle, the "return current" for it is essentially travelling in the oppposite direction from the other, and the white lead ends up carrying back only the difference between the two currents, so it never has a current greater than the load on ONE of the two halves.
Where I live in Ontario, Canada, these split receptacles, fed by 14/3 cable, are mandatory around kitchen counters. They each provide in one outlet box TWO circuits of 15 amps max, each with only one place to plug in a load. You are not allowed to connect more than one of these Split Duplex receptacles to one dual breaker, so each half of the outlet is a dedicated 15 A circuit. So around my kitchen counter there are three such boxes, plus a fourth near the table, providing a total of 8 separate 15-amp circuits. In the USA where these outlets are done as dual receptacles fed from 20 amp breakers (12/3 cable), four such boxes would still provide 8 sockets to plug into, but only a total of 4 separate circuits.
By the way, trying to use the push-in hole on the back for a connection to another box further down the line may technically avoid the rule about not using the screws for making junctions between wires, but it clearly violates the basic intent that all junctions of cunductors in a circuit should be made with wire nuts or similar devices designed to ensure solid connections (electrically and mechanically).
Question for those clear on the NEC: As I said, where I live there can be only ONE Split Duplex receptacle on a 14/3 cable from the panel, and no further branches are allowed. In the USA with 12/2 cables to the dual (20 amp) receptacle for heavy loads in a kitchen, are you allowed to have further branches beyond the first box?
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