How to Make a 220-volt Extension Cord for a Welder

Cut a piece of 3-conductor, 12-gauge power line to the length you desire for your extension cord. Remove 2 inches of the outer jacket on each end of the line, and then 1/2 inch of insulation from the ends of the black, red and white leads of the cable.

Slide one end of the power line through the hole in the back of the gang box -- a plastic or metal box designed to hold electrical outlets and switches, either in walls or externally -- and then through the cable clamp. Pull several inches of power line out of the front opening of the gang box.

Loosen the three screws on the back of the 220-volt socket. Attach the red and black wires to the outer two screw terminals and tighten the screws. Attach the white wire to the center screw terminal and tighten the screw. Pull the wire from the back of the box to seat the socket in the gang box. Tighten the cable clamp to hold the wire, then screw the socket into the gang box at the attachment points with the socket's screws.

Loosen the cable clamp on the back of the 220-volt plug and the screw on the face of the plug that holds the outer cover in place. Slide the end of the power line through the clamp and place the cover onto the line.

Loosen the three screws on the back of the 220-volt plug. Attach the red and black wires to the outer two screw terminals and tighten the screws. Attach the white wire to the center screw terminal and tighten the screw. Slide the cover back onto the plug and tighten its screw. Tighten the cable clamp to hold the wire.