Anatomy of an Electrical Service Panel

The two thick black hot service wires feeding the Main each carry 120 volts from the electric meter and feed the two "Hot" electrical bus bars in the panel. These bus bars provide power to the circuits. By varying how many bus bars a circuit breaker connects to, that determines if it is providing 120 volt or 240 volt electricity to a circuit. Single pole circuit breakers provide 120 volts and connect to just one hot bus bar. Double pole circuit breakers provide 240 volts to a circuit and plug into both hot bus bars. The electrical current leaves the service panel through the black power wire and is on its way to your electrical device.