I ain’t an electrician, but this should be a no-brainer of a task especially after watching a few Youtube videos. This question concerns a regular house outlet in the US with two sockets. In Video “A”, a two-socket outlet being replaced had only one pair of wires feeding the outlet. Once replaced and the single pair connected, it was demonstrated that both sockets worked when finished (using just one pair of wires). Does this make sense?
In contrast, Video “B” (that matches my case), a two-socket outlet had two pairs of wires feeding the outlet. It seems logical that one pair of wires would serve only one socket. So, I am confused why does the scenario in Video “A” work? And, furthermore…why the need for one pair vs. two pairs of wires to feed a two-socket outlet?
There is basically only one “wire pair” in the whole house, going back to the same source no matter how many different wiring runs are made. (Actually, there are two in most modern houses, one 120VAC pair from each bus of the 240VAC service, but never mind.)
So if two wires are run to the same wall box, it’s only a minor difference in current capacity and ability to separately protect each socket. One wire to the first socket, daisy-chained with a short loop to the second, is electrically and functionally equivalent.
HOWEVER, if there are two wire pairs and one socket, what’s going on is a “daisy chain” scheme - the power comes in one wire pair, feeds the socket, and goes out the second pair to the next socket or light switch on the chain. You have to connect both pairs to the same socket for everything to work right.
The two outlets are joined by a break-away jumper.
If you want them to be on the same circuit, you leave the jumper in place, and feed with one hot and one neutral.
If you want two circuits, you break the jumper and feed as you see fit (usually one ends up being switched).
In simpler terms, one of the two outlets is connected to a wall switch.
You know how some homes have an electrical switch which doesn’t seem to turn anything or or off? Yeah… that’s because you don’t have anything plugged into the wall outlet that is controlled by that particular switch.
As mentioned above:
A standard duplex receptacle has 5 screws under which the wire is landed. Many older and almost all newer receptacles have two brass and two silver colored screws plus a ground screw.
You’ll notice that the two brass screws(hot side) are connected by a small breakaway tab. Ditto for the silver neutral(misnomer) side.
One set of wires feeds your device, one set feeds the next device(likeliest scenario, but may be half switched or some other thing as mentioned by beowolf if tabs are missing) via the small breakaway tabs.
I note you mention pairs of wires. Do you have a ground wire at the location you’re going to swap your own receptacle?
A: This outlet was designed (by the electrician) to have each individual socket be on an independent circuit (Amateur Barbarian’s first hypothesis). This can happen in kitchens, for instance. In this case, you’re supposed to break the little jumper tabs on either side of your new outlet module, and make sure not to mix up the two black wires or the two white wires.
B: This outlet was designed to have one socket controlled by a wall switch and the other permanently on (QuickSilver’s hypothesis). This happens in bedrooms and living rooms. Again, in this case, you’re supposed to break the jumper tabs on either side of your new outlet module, and again avoid mixing up the wires.
C: This outlet is part of a daisychain (Amateur Barbarian’s second hypothesis): another socket or lamp relies on this outlet to get its own power, so you have incoming wires and outgoing wires. In this case, the jumper tabs should stay on. Both black wires on the same side (narrow slot), both white wires on the same side (wider slot).
The simplest way to determine what’s needed is to look at the old outlet module you’ve taken out. If it had its jumper tabs in place, your new outlet needs to have them too.
