Things You'll Need
Black permanent marker
Double-pole circuit breaker
Neon voltage tester
A standard 110- to 125-volt outlet converts easily to a 220- to 250-volt outlet. The main consideration during the conversion is the ampacity of the wires, which must conform to the National Electric Code Wire Ampacity Table 310-16 for the amount of current they will carry. The new receptacle will have a different plug configuration than the old receptacle and will no longer accept 110- to 125-volt plugs. This conversion is suitable only for 15- and 20-ampere outlets and not for ranges or dryers. The outlet must be the only one on the circuit.
Service Panel Changes
Turn off the main circuit breaker and remove the screws that hold the cover on. Note that the wires and the terminals on the main circuit breaker always carry electric current even when the main circuit breaker is turned off. Do not touch them for any reason.
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Loosen the terminal on the circuit breaker that controls the outlet, using a screwdriver. Remove the wire. Carefully pry the circuit breaker out of the panel with a flat-head screwdriver at the center of the panel and remove it.
Follow the white neutral wire for the outlet to the neutral bus bar. Loosen the terminal screw and remove the neutral wire from the bus bar. Color the last 3 inches of the neutral wire black using the permanent marker. This wire comes into the box inside the same cable as the black hot wire.
Install the new double-pole circuit breaker in the panel by hooking the tabs on the back of the circuit breaker on the lock bar and pressing it in at the center until it snaps into place. Turn the circuit breaker to the "Off" position.
Loosen both terminal screws on the new circuit breaker. Insert the bare end of the wire that was previously connected to the original circuit breaker into the terminal and tighten the screw. Repeat this for the re-coded neutral wire and the second terminal on the circuit breaker.
Reattach the service panel cover and secure it with the screws. Make sure that the new double-pole breaker is in the off position and turn on the main circuit breaker.
240-Volt Outlet Wiring
Verify that the power to the outlet is off by inserting the neon voltage tester leads into the outlet. The lamp stays off if no power is present. Remove the screw securing the outlet cover and remove the cover. Remove the screws that hold the outlet in the wiring box and pull the outlet out of the box.
Loosen the terminal screws for the bare ground wire, the white neutral wire and the black hot wire. Remove the wires from the terminals.
Place the bare ground wire on the green ground screw of the new receptacle. Terminal connections should have the U-shaped wire end wrapped clockwise around the terminal screw. Tighten the ground terminal screw.
Color the last 3 inches of the white neutral wire black using the permanent marker. Place the black wire on one terminal and the re-coded neutral wire on the other terminal. Tighten both terminals.
Fold the wires behind the receptacle as you push it back into the wiring box. Screw the receptacle to the wiring box using the supplied screws. Place the cover over the outlet and fasten it in place with the screw.
Turn on the circuit breaker and test the new outlet with the neon voltage tester. The light will turn on to verify that the outlet is wired correctly. The voltage tester will light two lamps instead of one to indicate 240 volts rather than 120.
This is a good way to convert an outlet for an appliance such as an air conditioner when that outlet is the only one controlled by the circuit breaker. Replace circuit breakers with another circuit breaker that has the same or lower current rating. The current rating is listed on the breaker's switch handle. This ensures that the wires are still protected against overloading.
You must verify that the circuit breaker controls only the outlet being converted. The circuit breaker must not control any other receptacles or light fixtures. Always turn the power off to work on your home's electrical system.