A four-prong 240-volt twist-lock plug is one that is approved by the National Electrical Manufacturers Association (NEMA) for production and sale in the United States. A four-prong plug has two hot wires, a neutral wire and a grounding wire. The plug is designed to lock onto a matching receptacle by twisting the plug clockwise when you insert it. Wiring the plug is fairly straightforward and requires only a few basic tools.
Unscrew the cover of the 240-volt twist-lock plug with a screwdriver. View the terminal screws at the back of the cover and loosen each terminal screw by turning it counterclockwise.
Remove 1 inch of sheathing from the tip of the electrical cable with a utility knife. Strip off 1/2 inch from the tip of each exposed wire, using a wire stripper. Twist the strands to keep them from fraying. Loosen the clamp screws located on top of the plug handle. Slip the cable through the opening on top of the plug, then pull the cable from the other end of the plug.
Hook the wires around the terminal screws on the plug cover in the following order: black wire (hot) to a brass terminal screw, red wire (hot) to another brass terminal screw, white wire (neutral) to the silver terminal screw and green wire (ground) to the green terminal screw. Tighten the screws to secure each connection.
Trim any excess wire with diagonal pliers. Replace the cover of the 240-volt twist-lock plug and tighten the holding screws in front of the plug cover. Tighten the clamp screws on top of the plug handle to secure the electrical cable.