Under what circumstance can a cable assembly shield serve as an equipment grounding conductor?

A cable assembly shield can serve as an equipment grounding conductor when it is rated for fault clearing time. This condition is crucial because the shield must be capable of handling fault currents without failure for a specific period, allowing the overcurrent protection devices to operate effectively. This ensures safety in the electrical installation by providing a reliable path for fault currents to trip circuit breakers or fuses.

In applications where the fault clearing time is compromised, such as with basic insulation or improper installations, the cable shield may not function effectively as a ground path. Therefore, the rating for fault clearing time indicates the assembly's ability to safely contribute to the grounding system under fault conditions, ensuring that it's both safe and compliant with electrical codes.

The other conditions, such as being insulated or having a voltage rating, do not directly address the necessity for a cable assembly shield to be able to carry fault currents responsibly. Additionally, while specific applications like residential use or voltage thresholds can dictate safety standards and practices, they do not determine the functionality of the cable assembly shield as a grounding conductor in terms of fault clearance.