An impedance grounded system rated 480 volts to 1,000 volts is permitted under what condition?

An impedance grounded system rated between 480 volts to 1,000 volts is typically permitted under specific regulatory conditions, primarily focusing on safety and system integrity. Such systems allow for limited grounding techniques to reduce fault currents while still providing a path for electrical faults.

In general, impedance grounding is often used to achieve desired transient behavior during fault conditions and to minimize damage to equipment. However, the use of an impedance grounded system in this voltage range depends on adherence to established codes and standards, which may not be met simply by being grounded, being part of a three-phase system, or undergoing monthly inspections, as described in the other options.

The implication here is that adherence to the necessary codes, standards, and maybe site-specific regulations governs the acceptance of such systems. Therefore, without meeting more stringent conditions or regulatory frameworks that go beyond the basic criteria provided, the status of "none of the above" correctly indicates that without explicit guidelines or compliance requirements, the system's permissibility cannot be established.