When are supplemental equipment grounding conductors required according to NEC® 250.118?

Supplemental equipment grounding conductors are necessary when specified by the circuit designer as a part of the overall electrical system design. The National Electrical Code (NEC) recognizes that the circuit designer may have specific requirements based on the application, load characteristics, or particular safety needs of the installation. This allows for a tailored approach to grounding that enhances safety and mitigates potential issues in systems with varying conditions or operational demands.

The other choices address different scenarios that may require grounding considerations, but they do not encompass the broader range of situations that a circuit designer might identify as needing supplemental grounding. For instance, corrosive atmospheres may warrant additional grounding measures, but that requirement doesn't encompass all potential applications as dictated by a designer's specs. Similarly, high fault currents and the method of wiring being non-galvanized are only two aspects that might influence grounding requirements but are not universally applicable in the same way as a designer's specifications.