Association of Home Appliance Manufacturers
How to Make a Shockproof Three-Wire Extension Cord
Current electrical codes require that all outside outlets and those in the bathroom, kitchen, or other damp areas be protected by a ground fault circuit interrupter (GFCI). New homes must have these protective devices, but homes built prior to 1974 have only grounded circuits with circuit breaker or fuse protection, which will not ensure your safety.

Double-insulated tools and tools with a three-wire grounded cord offer good protection against shock, but many times their safety feature can be interrupted by either accident or improper use. Your best guarantee of safety is to assure that everything you use outdoors or around damp areas is plugged into a GFCI, which is an electrical devise that instantly detects a hazardous situation and cuts the flow of power before a fatal shock is delivered.

A GFCI device senses the current flowing to and from electric tools and equipment. Under normal operating condition, the current flowing to the tool is the same as that returning to the electrical panel. If a ground fault should occur, some of the current is diverted to ground by a short somewhere in the circuit. You'll be electrocuted if the short is through you to the ground. The GFCI can sense a current flow imbalance of as little as 5 milliamps (which can't hurt most people) and almost instantly shuts down the current.

You can make a shock-proof extension cord using any standard 3-wire cord by adding one of these devices to it. It's a simple job to replace the standard female end of the cord with a GFCI devise housed in an exterior box fitted with a weatherproof cover.

Metal exterior outlet boxes come threaded for box connectors. Plastic boxes may be threaded but many brands require an adapter. If you plan to use a plastic box, get the necessary plastic parts so the box can accept a standard clam-type box connector.

To make a GFCI extension cord, you'll need a 25 ft., 3-wire (14-3) extension cord in good condition, a GFCI receptacle device, a weatherproof gang rectangular outdoor box with weathertight cover, 1-clamp type box connector, combination tool (wire cutter, stripper), channel lock type pliers, and, a screwdriver.

Here's How

Cut off the female receptacle of your extension cord with a wire cutter and strip about 6 in. of the outer cover from the end of the cord, being careful not to cut the insulation of the inner conductors. Remove the insulation to expose a black, white, and green wire. Strip away about 1/2-in. of insulation from the ends of each wire.

Screw the box connector into the end of the box and tighten it with the channel lock pliers. Loosen the clamp and pass the end of the extension cord through the connector into the box. Pull a foot or so of the cord into the box so it is easy to wire up the GFCI device.

The device has either screw-type terminals like a standard receptacle or it may have wire leads. In either case, you must connect the extension cord wires to the terminals or lead out wires marked LINE. If the device is like the one pictured with screw terminals, wrap the black wire clockwise around the copper-colored terminal screw. Tighten the screws and check to see there are no frayed strands that will short out against the box.

Wrap the white wire around the silver screw in the same way, then connect the green ground to the green screw at the top of the device. If you use a metal box, run a short section of wire from the green screw on the GFCI device to the grounding screw inside the box. Use wire nuts to connect the cord to the device if it is equipped with wire leads instead of screw terminals.

Pull most of the cord out of the box to make room for the GFCI. Secure the device in place with the mounting screws provided. Check that the protective outer cover of the cord is still inside the box and then tighten the screws on the box connector to clamp the cord in place. Put the gasket in place and install the cover with the two screws provided.

It is possible to wire more receptacles to this device. Connect short jumper wires to the LOAD terminals on the GFCI and attach them to matching terminals of a standard receptacle. This receptacle and all others installed downstream of the device will have GFCI protection. If you purchase a 2-gang box and weatherproof lid and an additional receptacle, you will be able to plug four cords into the box and have all protected by the GFCI. This may be handy if you need to run several tools and don't want to be constantly changing cords. If you plan to run more than one tool at a time, you need a heavier cord, at least 12-3 gauge.

Written by the editors of HouseNet
Copyright HouseNet, Inc.

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