What Determines the Circuit Breaker Size?

The load a circuit is to carry determines the appropriate size circuit breaker. For safety, the total circuit load should be 80 percent of the breaker's capacity. This allows for factors such as ambient temperature and its effect on the operation of the circuit, according to Electrical Construction & Maintenance.

Manufacturers print the amperage rating of appliances and electronics on the device. The amperage of the circuit is the sum of the appliances operating on it. If this number is greater than 80 percent of the capacity, one or more of the appliances should operate on a different circuit or the capacity of the circuit increased.

Increasing the capacity of a circuit requires more than just changing a circuit breaker in the electrical panel. Drawing too much power through a circuit produces additional heat, creating a fire danger regardless of the circuit breaker rating. Circuit breakers work to protect wiring and trip before overheating becomes a problem. A 15-amp breaker requires a minimum of a 14-gage copper wire. Increasing to a 20-amp breaker increases the minimum wire gage to a 12-gage.

Electrical codes specify the appropriate size breaker for each circuit. They require permanently installed and operated appliances like refrigerators and air conditioners to have a dedicated circuit.