How to Install a 240-Volt Circuit Breaker - The Spruce Continue to 3 of 10 below. A 3-wire, 240-volt circuit has two hot wires—each supplying 120 volts for a total of 240—and an equipment ground wire. A 120-volt circuit has only one hot wire connected to the breaker plus a neutral wire connected to the neutral bus bar Author: Bob Formisano Understanding 220 or 240 volt Electrical Circuits - nojolt Understanding 220 or 240 volt Electrical Circuits. This is why 240 volt circuits connect to double pole breakers that are essentially two single pole breakers tied together. In the main panel, every other breaker is out of phase with the adjoining breakers. So, in essence 240 volt wiring is powered by 2 - 120 volt hot wires that are 180 degrees out of phase.