What determines the rating of a branch circuit?

The rating of a branch circuit is determined primarily by the overcurrent protective device. This device, which includes circuit breakers or fuses, is designed to protect the wiring and connected devices from excess current that can cause overheating and potentially lead to fire hazards. The rating of this device establishes the maximum amount of current that can safely flow through the circuit without triggering the protection mechanism.

By specifying the current rating, the overcurrent protective device directly influences the overall capacity of the branch circuit. Therefore, the branch circuit's rating must align with the capacity of the protective device to ensure safety and compliance with electrical codes.

While operating equipment, outlet types, and insulation type are important considerations in circuit design, they do not establish the fundamental rating of the branch circuit itself. The overcurrent protective device takes precedence in determining safe operating limits for the entire circuit.