How to Wire a 240 Volt Circuit

by G.K. Bayne

Wiring a 240-volt circuit is a simple matter if you know a few basic steps and take some precautions for safety. A basic understanding of electricity is helpful.

Place those safety glasses over your eyes before you attempt any electrical work. Before you remove the cover that protects you and the circuits on your circuit breaker box, remove or disconnect all power to that box. This can be accomplished by the main breaker below your electric meter, or there may be a main breaker at the top of the circuit box you are working on.

Remove the screws that are holding the cover in place and set them in a safe place where you will not lose them. Take your volt-ohm meter and turn it to the voltage position to check that the main power is off. You can place the leads one each to each of the main bus bars that are running down the center of the box. The meter should read 0. To wire a 240-volt circuit, you must have a double-pole circuit breaker. This breaker takes power from both of the main bus bars. Each bus bar measured to ground will provide 120 volts, so both bus bars will provide 240 volts.

Install the breaker as per the manufacturer's instructions. Some breakers are a simple "snap in place," while others may need two installation screws to hold onto the main bus bars. Once you have the breaker in place, strip back the main conductor wires approximately 1 inch. For most applications, this may be a black-and-white wire with a bare copper in the middle of the electrical wire cable. Screw the wires into the circuit breaker's termination holes and tighten firmly--one wire to one screw termination. The bare copper wire will be connected to the grounding termination strip mounted to the back of the breaker box. This strip is generally located to the side of the bus bars.

Wire the device you want to operate from the 240-volt circuit. Strip all wire back approximately 1 inch from the end. Take one pair of wires, one from the new power source and the other from the device, and twist together using the wire pliers in a clockwise motion. Twist, again in a clockwise motion, a plastic wire nut over this connection and wrap with a couple rounds of electrical tape for extra protection. Repeat with the other pair of wires and the grounding wire. Reinstall the cover on the circuit breaker box and switch back on the main power.

Items you will need

  • Double-pole circuit breaker
  • Two wires with ground electrical wire cable
  • Safety glasses
  • Wire pliers
  • Wire strippers
  • Volt-ohm meter
  • Screwdrivers, Phillips and slotted
  • Plastic wire nuts
  • Black vinyl electrical tape

Tips

  • Follow all state and local codes when performing any electrical work.
  • Install the correct-sized circuit breaker for the device you are connecting to; this information will be provided by the manufacturer of any electrical equipment.