How should grounding conductors be sized according to NEC?

Grounding conductors should be sized according to the largest ungrounded conductor supplying the system. This approach ensures that the grounding conductor can effectively handle potential fault currents that may flow through it if a fault occurs in the system. The reasoning lies in the need for safety and protection; if a fault occurs, the grounding conductor must be able to carry sufficient current to trip the overcurrent protection device, such as a circuit breaker or a fuse, to prevent electrical fires or damage.

The National Electrical Code (NEC) provides tables and guidelines detailing the appropriate sizing for grounding conductors based on the size of the largest ungrounded conductor. This standard ensures consistency and safety across various electrical installations, thereby reducing the risk associated with ground faults.

Sizing based on the smallest ungrounded conductor would not provide adequate protection for the entire system as it may lead to insufficient capacity to handle fault conditions. Similarly, considering the type of load connected or the length of the grounding conductor does not correspond with the critical factors that impact the grounding system's ability to perform its functions during fault conditions. Thus, focusing on the largest ungrounded conductor is paramount for maintaining the safety and reliability of the electrical installation.