You may find that you have extra wires when you are wiring an electrical outlet. Don't just try to twist similar wires together and stick them under one terminal screw, because the wires could come loose and cause problems with your circuit. If in addition to the electrical cable entering the receptacle box you have an electrical cable or cables leaving the box to feed other receptacles downstream, you'll need to use jumpers to wire the receptacle correctly.
Things You'll Need
Turn off power to the circuit. Cut a 6-inch section of electrical cable and remove the sheath to separate the three wires inside. These wires will be your jumpers.
Splice wires of the same color together – black, white and bare (or green). First, strip 5/8 inch to 3/4 inch of insulation from the end of each wire in the receptacle box, and from both ends of each jumper. Next, hold the wires for each splice parallel (including the jumper) with the ends evenly lined up. Clamp your pliers over the ends and twist the wires together clockwise with four to five turns. Each wire should spiral around the others.
Twist a wire connector onto each splice until you feel resistance. If the connector does not completely cover the bare wires, use a larger connector or remove the connector and cut off enough wire from the splice so that the connector completely covers the bare wires. At this point, you should have three completed splices in the receptacle box and the only loose wires should be the jumpers.
Connect the loose jumper wire ends to the receptacle. Put the black jumper under the gold screw, the white jumper under the silver screw and the bare or green jumper under the green screw. Use a screwdriver to tighten the screw terminals onto the wires.
Bend the wires so they fit neatly into the receptacle box. Push the bare or green wires into the box first, followed by the white wires and then the black wires. Attach your receptacle to the box with the supplied screws and then screw on the cover plate.
You can also use this technique if you want to wire your electrical outlets in a parallel series. This allows you to disconnect an upstream outlet without cutting off power to downstream outlets.