Breaker Size Vs. Wire Size

Sizing

• Determine what applications will be powered by the breaker. You can use the breaker to power several electrical lines or wires. For example, one breaker controls the electrical power to one room in the house, including the outlets, lights and ceiling fans. These outlets and lights have multiple wires running to the power supplies, but all of these wires are attached to one breaker. Knowing what appliances you will be operating in the room will determine the size of the wires and the size of breaker required.

Voltage

• Most homes are capable of transmitting 120 to 240 volts to different parts of the house through the breakers in the electrical panel. The amount of voltage will also determine what size breaker and wire you will require. The room outlets, lights and ceiling fans operate off of 120 volts and your stove or clothes dryer operates off of 240 volts. Each one of these voltage requirements has a different wire and breaker size.

Amperes

• Amperes is the most important thing to know when sizing the breakers and wires. The amount of amps being drawn by an appliance or a room will determine the wire size. Even though you will always use one breaker to power an electrical system, knowing how many amps that electrical system will pull from the breaker will determine its size. The same is true with the wiring, but the size of wire also plays a role in your calculations.

Gauge

• One difference between sizing the breaker and sizing the wire is the wire must be a certain gauge to power the amount of current being sent through the wiring system. The measurement of the diameter or cross-section of an electrical wire is considered its gauge. The amperage required determines the gauge of the wire. The more amps required, the larger the wire.

Types

• Unlike breakers, which only require knowledge of the amps and voltage required, electrical wire sizing is determined by voltage, amps and the type of material used to manufacture the wire. Electrical wire is made from copper or aluminum. Either one of these materials will determine what gauge of wire you require, as well as knowing the voltage and amps required. Breakers do not have this problem. Copper wire is larger in gauge than the aluminum, but conducts electricity better than aluminum. For example, you use a 10-gauge copper wire compared to an 8-gauge aluminum wire.