If you closely examine a standard household electrical wall switch or outlet receptacle, you will notice that in addition to the screw terminals on the side of the device, there is a series of slots or holes in the back of the body. These are push-in wire connections, designed so that you can make wire connections simply by inserting the bare end of the circuit wire into the opening, where a spring clamp is supposed to hold it correctly. You might think that it's much easier to make a wire connection this way, compared to bending a wire into a loop and securing it around a screw terminal.
But professional electricians almost never use these push-in connectors, and there's a reason why. No pro wants to be called back to a job to correct a bad connection, and push-in wire connections are much, much more likely to fail than the old standard, screw terminal connections.
The Problem With Push-In Wire Connections
In theory, each push-in connector is fitted with a very small spring metal clamp inside the body of the switch or receptacle. This clamp is supposed to grip the bare wire securely once it is inserted in the hole, releasing only if you insert the tip of the small screwdriver into the release slot next to the opening.
But this connection is notoriously insecure, and it doesn't really provide the degree of metal-on-metal contact necessary for a good electrical connection. The wires will easily turn into the push-in hole, and gradually work their way loose. And the sheer amount of metal-on-metal contact is very, very small with push-in connections, which can lead to overheating of the device. Once the device is disconnected and reconnected once or twice, the spring clamps tend to wear out and lose their ability to grip the wires at all.
Any electrician or homeowner who makes regular use of push-in wire connections very soon learns to avoid it in the future. Here is one instance in which the old way is the best way.
The Better Way
The other option for making wire connections is the traditional way: to secure the wires underwire terminal screws that can be tightened down tight. This method takes a little longer and requires a bit of practice to master. Usually, it means forming the bare end of the wire into a clockwise loop around the screw terminal, then tightening the screw down firmly to grip the wire. On some types of receptacles and switches, the bare wires are inserted into a small bracket, then the screw is tightened down to clamp the wire securely. Either type of screw terminal connection can be unfastened and reconnected as many times as you like—they will never wear out.
Whatever design is used on the switch or receptacle, using the side screw terminal connections will give you far better results than taking the shortcut and using push-in connections on the back of the device. In the long run, it's no timesaver if you end up returning to repair wire connections that fail.