This tutorial shows you the basic steps of installing a new 240-volt, 30-amp, double-pole circuit breaker for a new 30-amp appliance receptacle (outlet). The circuit includes two 10-gauge black hot wire conductors and a 10-gauge green ground wire conductor for a 3-wire system with no neutral. Some 240-volt appliance circuits use 4-wire circuits that include a neutral. Installing a circuit breaker involves working in your electrical service panel (breaker box), so you must be familiar with the parts of a panel and how it works to ensure a safe installation. This project may also require a building permit, depending on the rules in your area.
Switching off the main breaker shuts off the power to the panel's bus bars and all household circuit breakers but it does not turn off the power cables coming from the utility service lines. The cables and the terminals they connect to in the service panel remain live and carry deadly current—even when the main breaker is switched off. Never touch these conductors or terminals while working in the panel.
3-Wire Circuit Basics
A typical 240-volt, 30-amp circuit includes a double-pole circuit breaker, which has two terminals for the two hot wires. The wires usually are black or red, but one may be white if it is labeled as hot with a black or red stripe near each end. A 240-volt, 3-wire receptacle has three prongs (two hot and one ground) to accept a 3-prong plug. Plugs and receptacles for a 240/250-volt circuit can come in a number of configurations.
Note: New electric ranges and clothes dryers require circuits that provide 120 volts and 240 volts at the receptacle. These use four wires—black (hot), red (hot), white (neutral), and green (ground). The neutral wire is designed to carry an unbalanced load between the two phases of the circuit. The installation is similar to a 3-wire system but includes the fourth, neutral, wire that connects to the neutral bus bar in the panel and the neutral terminal on the receptacle. A 3-wire circuit is not suitable for a electric clothes dryer.
Double-Pole vs. Single-Pole Breakers
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 in the service panel.
Equipment / Tools
- Voltage tester
- Wire strippers
- 30-amp, 240-volt double-pole circuit breaker
Turn Off the Power
Open the door to the electrical service panel. Turn off the power to the panel's breakers and hot bus bars by switching off the main breaker. Remove the screws holding the door in position and carefully remove the door assembly. Remove the cover plate over the breakers (called the dead front panel), without touching any wires inside the panel. Confirm that the power is off by testing the branch circuit breakers (not the main breaker) with a voltage tester. If you detect any voltage at any breaker, call an electrician for help.
Do not touch the two hot service cables coming into the panel or the terminals (called service lugs) where the cables connect near the main breaker. These have power at all times unless the utility company shuts down your service feed.
Remove the Panel Knockouts
Rotate the dead front cover so you can work from the back side. Remove two adjacent knockout tabs for the new double-pole breaker, as needed. Knockouts either are loosened with a screwdriver blade and then removed with pliers or are simply grabbed with pliers and bent until they break off.
Secure and Strip the Circuit Wires
Feed the circuit wires into the box and secure them to the box as needed. Strip about 1/2 inch of insulation from each end of the two black (hot) wires and the green ground wire, using wire strippers.
Connect the Hot Wires
Connect each black hot circuit to one of the terminals on the circuit breaker. Make sure to insert the wires fully into the screw terminal and tighten the terminal screw securely using a screwdriver. Connect only one wire per terminal.
Install the Breaker
Install the breaker into the panel by tilting the breaker so that its tabbed end fits into the slots or mounting bar on the panel housing, then tilt the other end down until it snaps into place on the two hot bus bar knife blades.
Check for a Proper Fit
Confirm that the breaker is secure and completely snapped into place. It should be flush with the other breakers in the panel.
Connect the Ground Wire
Connect the circuit ground wire to the ground bar on the service panel by inserting the stripped end of the wire into an open slot on the bar and securing the wire tightly with the terminal screw. The ground wire must use an open slot on the bus bar; do not connect more than one wire to a single slot.
Complete the Installation
Complete the wiring connections and installation of the receptacle, following the manufacturer's directions.
Reinstall the dead front cover and the door on the service panel. Switch on the main breaker to restore power, and test the new circuit for proper operation.