Is it permissible for the copper ribbon or tape shield of a medium-voltage cable to serve as the required equipment grounding conductor for a circuit supplied by a 1,500-volt, solidly grounded system?

The scenario presented involves a medium-voltage cable that operates within a solidly grounded system at 1,500 volts. In this context, the requirements for grounding conductors are critical for safety and system functionality.

The correct response indicates that it is not permissible for the copper ribbon or tape shield of a medium-voltage cable to serve as the required equipment grounding conductor in this situation. The reasoning lies in the standards and codes applied to electrical installations. Specifically, the National Electrical Code (NEC) delineates specific requirements for grounding conductors, particularly for equipment connected to voltages above 1,000 volts. When dealing with higher voltage systems, like the one in question, the equipment grounding conductor must be designed to handle fault currents and ensure adequate safety measures, which often necessitates dedicated conductors rather than relying on cable shields.

Additionally, the copper shield may not provide the necessary conductance or fault current capacity required to effectively ground the equipment in this voltage range. This ensures proper operation of protective devices and minimizes risks associated with electrical faults. Therefore, under these guidelines, the assertion that using the shield as a grounding conductor is permissible is incorrect.