The size of the equipment grounding conductor is determined primarily by which factor?

The size of the equipment grounding conductor is predominantly determined by the rating of the circuit overcurrent protective device. This is because the equipment grounding conductor must be adequate to ensure safe disconnection of the electric supply in case of fault conditions, providing a path for fault currents to ground and ensuring the protection of equipment and personnel.

When a fault occurs, such as a short circuit, the overcurrent protective device is designed to trip and interrupt the excessive current flow. The capacity of the equipment grounding conductor must be sufficient to handle the fault current likely to flow through it until the protective device operates. The National Electrical Code (NEC) specifies minimum sizes for grounding conductors, based on the rating of the protective device, to ensure that the equipment grounding system is effective in maintaining safety.

The other factors like the cross-sectional area or material of the phase conductors and the type of raceway do play roles in the overall electrical installation and its performance, but they are not the primary determinants for sizing the equipment grounding conductor. The emphasis on the protective device rating stems from the need to ensure reliability and safety in grounding systems in the event of electrical faults.