For a steel metal cable tray used as an equipment grounding conductor with conductors protected by a 100A circuit breaker, what must the cross-sectional area be?

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The requirement for the cross-sectional area of a steel metal cable tray functioning as an equipment grounding conductor is derived from the National Electrical Code (NEC) guidelines that govern grounding conductor sizing. For grounding conductors, the minimum cross-sectional area must sufficiently handle the expected fault current without exceeding temperature ratings and ensuring system protection and integrity.

In the case described, with a circuit breaker rated at 100A, the NEC specifies requirements based on the size of the circuit breaker and the fault current it is expected to interrupt. The code typically stipulates a cross-sectional area that will adequately support the ground fault protection needed for safe operation.

To meet the requirements for connectivity and safety, a steel metal cable tray must have a minimum cross-sectional area of 0.40 square inches when used as an equipment grounding conductor for a system protected by a 100A circuit breaker. This sizing ensures that the tray can effectively handle fault currents without failure, thus maintaining the safety of the electrical system.

That is why the option reflecting a cross-sectional area of 0.40 square inches aligns with the standards established in the NEC for grounding conductors.