If circuit conductors are installed in parallel, how should the equipment grounding conductor be sized?

When circuit conductors are installed in parallel, the sizing of the equipment grounding conductor can be done based on the overcurrent protective devices associated with either the feeder or the branch circuit. This approach recognizes that parallel conductors may carry equal currents and therefore a single grounding conductor can effectively provide a path for any fault current that could occur in either circuit.

The regulation for grounding conductors indicates that the equipment grounding conductor must be adequately sized to handle the maximum fault current that could be provided by the overcurrent protective device serving the associated circuits. Since both the feeder and branch circuits could contribute to ground fault scenarios, considering either allows for flexibility, ensuring that the grounding system remains effective and compliant with safety regulations.

This comprehensive approach—considering both types of circuits—ensures that the system provides adequate protection without being overly conservative, which could lead to unnecessary expenses in grounding conductor size.