Things You'll Need
Sheathed cable in the appropriate gauge
240V circuit breaker sized to the appliance
240V outlet for specific appliance type
Large gauge wire stripper
Long nose pliers
Neon voltage tester
Non-contact voltage tester
Old wiring methods may not have included a ground wire. Modern wiring requires all circuits to have a ground. New outlets will have either three or four poles. Three-pole outlets have two hot poles and a ground pole. Four pole outlets have two hot poles, a neutral pole and a ground pole.
Heavy cable is difficult maneuver, especially folding it back into the outlet box. Buy a box that is deeper and wider than appears necessary as this will make getting the wires in easier.
Verify procedures with your local building department before beginning. A permit may be necessary.
Some appliances use a combination of 120 and 240 volts. These appliances will have a neutral wire, others will not. The illustrations show a variety of 240 volt outlets and identify the poles on each.
If your sheathed cable has a neutral wire and the neutral is not used, do not connect it in the circuit panel or in the outlet box. Just snip it off where it enters the box.
If your outlet box is metal, be sure to ground the box as well as the appliance. Connect the bare ground from the cable to a green ground screw and run a short piece of bare or green insulated wire to the receptacle.
Use 12-gauge wire for 20 amp circuits, 10 gauge for 30 amp, 8 gauge for 40 amp and 6 gauge for 50 amp.
If the appliance uses a combination of 120 and 240 volts, buy three-wire cable. If it only uses 240 volts, buy two-wire cable. Both types have an extra, bare wire for ground.
Doing electrical work may potentially expose you to dangerous electrical current. Always turn off the power before beginning, verify the power is off by testing and do not turn the power on until you are ready to test.
Although this installation is simple enough for any beginner to accomplish safely, if you are unsure or do not feel confident in your ability, hire a qualified electrician to do the work.
Always use tools designed specifically for electrical work when working on your homes wiring.
Skimping on wire gauges and outlet sizes is unsafe and potentially creates a fire hazard. Always use the proper gauge wire and outlet for your appliance.
Do not use obsolete, ungrounded receptacles. They are dangerous and may allow electric shock or cause a fire.
Larger home appliances, such as electric ranges, dryers and some air conditioners, use a 240-volt supply rather than the usual 120 volts. Installing an outlet for these appliances is no more difficult than than installing a standard 120-volt wall outlet. The main difference is that different appliances use various types of outlets.
Determine the amperage and voltage requirements of the appliance being installed. The product should ship with a label attached that specifies voltage and current requirements. Product documentation should contain the same information. Purchase a 240-volt outlet, circuit breaker and sheathed cable to meet the power requirements of the appliance at your local hardware store or home center.
Install the 240-volt circuit breaker in the circuit panel. Turn the main circuit breaker off. Remove the panel cover and locate two adjacent open positions. Snap the new double breaker into place. Pull the new sheathed cable into the circuit panel, remove the sheathing and strip 3/4 inches of insulation from the wires. Make the connections to the ground and neutral bus bars before connecting the two hot wires to the new breaker. Reinstall the panel cover. Make sure the new double breaker is turned off before turning on the main breaker.
Run the sheathed cable to the appliance location and install the new receptacle box there.
Strip the cable sheathing away from the cable and run it into the outlet box using the appropriate bushing or connector. Strip 1/2 inch of insulation away from each conductor that will be used.
Make the ground connection. Insert the ground wire into the ground lug on the receptacle and firmly tighten the screw. In the illustrations, the ground lug is labeled "G".
Make the neutral connection next if there is one. Not all outlets have a neutral lug. Outlets with three lugs do not have a neutral (see Tips). In the illustration, these lugs are labeled "W".
Make the two hot connections. Insert the colored wires into the hot lugs and firmly tighten the screws. These lugs are commonly labeled with L1 and L2. It does not matter which hot wire is connected to which lug as long as both are hot and not neutral or ground.
Push the wires into the outlet box and screw the outlet to the box. Install the outlet cover and turn on the power to the outlet for testing.
Test the outlet using the neon voltage tester. The voltage between the two hot poles should be 240 volts. The voltage between one hot pole and the neutral pole (if there is one) should be 120 volts. Repeat the hot-neutral test between for the other hot pole. Finally, test the voltage between the ground pole and one hot pole. This should also be 120 volts.
Michael Logan is a writer, editor and web page designer. His professional background includes electrical, computer and test engineering, real estate investment, network engineering and management, programming and remodeling company owner. Logan has been writing professionally since he was first published in "Test & Measurement World" in 1989.