Things You'll Need
40-amp double pole breaker
A 240-volt circuit has two hot wires that together make up 240 volts; each wire carries 120 volts. There is also a ground wire; it will be colored green or copper. In a 240-volt circuit there is no neutral wire. You can wire a 240-volt circuit to provide both 120 and 240 volts. For a generator 240-volt connection it is best to wire it direct and with only 240 capabilities. The generator is an additional power source or a backup source. You want to keep the wiring dedicated to the need of the generator since its purpose is for additional or emergency power.
Turn off the main power supply leading into the house. Use a volt meter to test the termination of electricity into the breaker panel. Do not work in the breaker panel if electricity is still flowing.
Strip the 8/3 cable a 1/2 inch from the end exposing the wires. Use a stripper tool for a cleaner cut. Strip the ends of these three wires a 1/2 inch as well.
Screw the two black wires to the circuit breaker The circuit breaker has two screws that each hold one black wire. Insert the wires fully by pushing them into the terminal and tighten the screw securely.
Install the breaker into the service panel. Set the breaker in the housing in the service panel where you want the circuit to reside. Rock the circuit back and forth: inserting the tabbed end of the breaker into the housing first and then snapping the rest of the breaker over the hot bus bar.
Look at the double pole breaker to make sure it fits snug. The breaker for a 240-volt installation is a double pole breaker because of the two 120-volt hot wires totaling 240 volts.
Thread the ground wire through the ground bar and run the wire to the end of the 240-volt receptacle in the breaker box. Screw the ground wire to the end of the 240-volt receptacle.
Run the 8/3 cable to the outlet you want the generator to plug in to. Attach the two black wires to the screws that aren't colored and then attach the ground wire to the green screw.
Attach the outlet to the wall after the 8/3 cable is secured. Go to the main power supply and turn it on. Next push the breaker to the "On" position. Plug the generator into the outlet and start it up.
In order to comply with code, the two line voltage wires feeding into the 220-volt circuit need to be the same color black or red. You can mark the wires with tape if necessary.
An 8/3 cable works for a 40-amp breaker.
De-energizing of the main panel doesn’t always occur by shutting off breakers. Use a volt meter to test the termination of electricity. Death can occur from electric shock.