Ensure the circuit breaker is to the Off position, then connect the wires to the terminals, the ground screw and the neutral screw. Install the breaker in the breaker box, and test it by turning the power on. If the breaker trips instantly, clear any short circuits.
Before installing a new breaker, use a voltage meter to ensure that no voltage is running through the main wires leading into the cabinet.
To begin, run the new cable into the circuit breaker cabinet, and secure it with a cable clamp. Then, connect the ground wire to the ground bus bar. Connect the neutral wire to the neutral bus bar. These wires may need to be stripped in order to fit into the bus bar.
Next, install the hot wire. Connect the hot wire to the breaker's terminals; around 5/8 inch should be stripped so it fits well. Once the hot wire is connected, the breaker is ready to be installed in the breaker cabinet.
Angle the breaker so that the breaker clips onto the bar on the right, and press it in. Then, press the breaker's left side until it clips in and completes the circuit. Finally, test the circuit, and label it for future reference.