A plug with a cracked or broken housing, a missing insulating cover or loose, badly bent prongs may present a fire or shock hazard or both; unplug it immediately and replace it. You might also want to swap a standard plug for one of a different color or a flatter one that takes up less room behind furniture.
Assuming that you don't mind losing a little cord length, cut the old plug off with wire cutters rather than trying to disassemble it.
Open the new plug according to the instructions. Some snap on and off the cord, and others screw together.
Insert about 6 inches (15 cm) of the cord through the plug's housing.
For a lamp or flat heater cord, split apart the two wires if they're not already split. Start the cut with a utility knife and then tear 2 inches (5 cm) apart by hand.
For a round cord, such as those used for some appliances and machinery, strip off the outer insulation. Make a 1-inch (2.5-cm) cut lengthwise at the cord's end; grasp the insulation to tear open about 3 inches (7.5 cm), scoring the surface with a utility knife as needed; and cut off the outer insulation at the top of the tear, being careful not to nick the wire insulation.
Unless the plug body is equipped with a clamp or another strainrelief connector, tie the two wires together using an Underwriters knot.
Determine how much wire must be exposed to reach and wrap around the terminal screws, then cut off any excess with wire cutters/strippers.
Remove 1/2 inch (12 mm) of the wire insulation with wire cutters/ strippers, using the stripper hole that corresponds to the gauge of wire you are stripping.
Twist the wire strands together and bend them to form a loop, then wrap each loop clockwise under the appropriate terminal screw.
For an ungrounded (two-prong) plug, attach the white or ribbed wire under the silver terminal screw or to the terminal on the wider prong, and attach the black wire (hot) under the brass terminal screw or to the terminal on the narrower prong.
When an appliance or tool requires a three-prong grounded plug, connect the grounding wire (green) under the green terminal screw on the grounding prong; attach the black wire (hot) under the brass terminal screw and the white wire (neutral) under the silver terminal screw.
Tighten any cord clamp or other strain-relief connector.
To install a quick- or self-connecting flat-wire plug, cut the end of the cord with wire cutters.
Installation varies. Either open an arm on the plug body, insert the cord and press the arm closed; or pull the terminal block and prong assembly out of the plug shell, feed the cord through the shell and into the terminal block, squeeze the prongs and push the two parts of the plug back together.
Appliances requiring 240 volts utilize cords with molded plugs and pigtails. Unplug the appliance and open the wiring-box cover with a screwdriver or nut driver.
Write "left," "center" and "right" on short lengths of masking tape and wrap these around the wires to identify the connection points. Remove and save the terminal screws.
Purchase an identical cord and connect its pigtails under the terminal screws, using the old cord as a guide. Reinstall the wiringbox cover.