How should equipment grounding conductors be sized in a conduit with multiple circuits?

When sizing equipment grounding conductors for a conduit containing multiple circuits, it is essential to base the size on the overcurrent protective device (OCPD) of the largest circuit. This principle is grounded in the intention to ensure effective grounding in case of a fault condition.

By sizing the equipment grounding conductor according to the OCPD rating of the largest circuit, you ensure that the grounding system will effectively manage fault currents from that circuit. It addresses the potential for maximum fault currents that could occur, providing sufficient capacity to carry those currents safely back to the ground. This is crucial for the protection of equipment and personnel.

Sizing based on the smallest circuit would not provide adequate protection in scenarios where a fault occurs in a larger circuit. Similarly, considering the total amperage of all circuits could underestimate the necessary capacity to handle fault currents from individual circuits. The length of the conduit run is not a factor in determining the size of the equipment grounding conductor; instead, it's the current rating and protective devices that are the focus of proper grounding practices.

Thus, selecting the equipment grounding conductor size based on the largest OCPD aligns with safety standards and ensures a reliable grounding system under fault conditions.