Wiring Residential Outlets.
Modern outlets use two conductors and a ground wire. For a description of this wire, its color codes and purpose see Residential Wire Described. There are two methods of connecting wire to an outlet.
In the first method, screw terminals hold a loop of stripped wire. On one side are a pair of silver colored screws. These are for connection of white wires. On the opposite side are a pair of brass colored screws. These are for connection of black wires.
I recommend using these screws to hold a small loop of stripped wire. The loop and the screw make a better physical connection. It is almost impossible to pull off or loosen. There is more wire surface bonded in the connection too so the electrical connection is also better.
The second method uses small holes in which the conductor wires are pushed in to make the connection. These holes are usually sized for #14 wire, which is the standard size for 15 amp circuits. If you are using #12 wire you must use the first method.
Two holes are on the "silver" side for white wires, and two holes are on the "brass" side for black wires. The conductors are stripped about an eighth of an inch and pressed in.
These holes are provided for the convenience (and speed) of electrical installers who may be wiring hundreds of outlets. If you're doing your own work, I suggest you take the extra five minutes per outlet and wrap the wires around the screws and fasten them down.
The ground wire must be fastened to the single screw terminal at the bottom of the outlet, usually colored green. This connection must be looped around the screw and tightened. A push in hole connection is not an option for the ground wire. If the outlet does not have a ground connection, it is obsolete and cannot not be used.