What is the use of a pigtail joint?

Answer 1

A pigtail joint is used where a number of wires must be consolidated into just one to make a connection. For instance, say you have an outlet box where you have to wire a receptacle. The only problem is you have too many wires. One comes from the breaker, one goes to the next recep, and a third goes to a light switch to feed the room light fixture. You have three hot wires, but there is no legal and safe way to terminate three wires on the recep. So, you cut a short piece of wire a few inches long. With the proper size wire-nut, you tie all three hot wires and your short piece (the pigtail) together. Now you have a single wire that will fit nicely on the receptacle. Of course, you would do the same with the neutral and ground.

Answer 2

The purpose of a pigtail is to allow a device (switch, receptacle) to be connected to a circuit in the following manner: So that a removal or failure of any device will not interrupt operation of any other device. Many building specifications will explicitly say to wire the job this way. It's also a smart idea that eliminates the possibility of cutting the branch circuit wire shorter each time the device is changed or maintained. If the pigtail gets too short you can just remove it and use a new one. The other option is to use the device as a 'bridge' and connect a set of wires coming into it and a set going out. Unfortunately this means that if the receptacle is at the beginning of the circuit, that connection must support the full load of all other receptacles. If the hot or neutral is loose, it can and will cause fire. With a pigtail, the device connection must only support the equipment plugged into that specific receptacle. The connection to receps down the line is made with twisted copper and a wire nut. This is much safer in regards to fire.