What determines the selection of the size of the overcurrent protective device?

The selection of the size of the overcurrent protective device primarily depends on the size and type of the conductors used in the circuit. This relationship is crucial because the overcurrent protective device, such as a circuit breaker or fuse, must be appropriately sized to protect the conductors from overheating due to excess current. If the overcurrent protective device is too large, it may allow excessive current to flow before tripping, which can lead to damage or failure of the conductors.

The National Electrical Code (NEC) provides guidelines that specify the maximum rating of overcurrent protection based on the ampacity of the conductors to ensure safety and prevent fire hazards. Therefore, understanding the characteristics of the conductors, including their size, insulation type, and material, is essential for selecting the correct overcurrent protection device.