I understand that from a quick look at the wiring technique, it may seems that it just makes good common sense to use both of the terminals when connecting two wires, within the junction box, to the two terminals on the receptacle.
Now, one has to ask oneself, “Is it the best connection and does it have its drawbacks?” The answer is NO and Yes. You see, although it is a secure connection and will function as a connection point, feeding power through the outlet, which is what you are doing, isn’t a great connection choice. Let me explain even further.
Let’s consider that there are three receptacles in this electrical connection run. The first receptacle is fed from the circuit breaker panel, via a circuit breaker. Then there’s a second wire that runs to feed the second receptacle. Basically, that’s one wire in and one wire out. Now, if you connect the feed wire to one of each of the terminals, both the hot and neutral terminals, then the outgoing wire connects to the other terminal. Between the two connection points on the receptacle is a metal link. This is the connection point that allows both halves of the receptacle to be powered.
In the case of split outlets, the common link is removed and you end up with two separately fed halves of one receptacle. This leads us to the dilemma that you can run into when dealing with wiring a receptacle to these two terminals.
Stay with me now! If you wire a receptacle using the terminals, instead of pig-tailing the wires, you are depending on the entire load of the two remaining receptacles and half of the first receptacle to flow through the link. But what happens if the link breaks or is overloaded? You will not only lose power to half of the first receptacle, but also the other two receptacles as well. This is very much like some Christmas light sets, where if you take out one bulb, the rest of the lights go out.
But don’t fret, there is a better way. It’s called pigtailing the wires and it is very simple to do. By stripping the ends of the two black wires, adding a length of black wire as the pigtail connection, twisting the three wires together using linesman pliers and covering the twisted connection with a wire nut, you have a continuous connection point that continually allows power to flow through the wires, while still allowing you to remove any one individual receptacle from the circuit without interrupting the others. Next, you’ll need to do the same to the white wires.
The next step is to simply strip the ends of the black (hot) and white (neutral) wires and connect them to the receptacle terminals. As you can now see, this is the correct and preferred connection method. If there’s any doubt, consider the problem that you would have if you had three wires in the junction box, but only two terminals on the receptacle. What would you do then? Would you double up the wires under one terminal? I certainly hope not! And while we’re on the subject of poor connections, I hope you all avoid using the push-in terminals on both receptacles and switches alike. This is a poor connection point and I absolutely beg you not to use these at any time, for your safety.