A facility has a 480-volt, 3-phase, ungrounded delta system. An electrician is installing new equipment. Which of the following statements regarding the equipment grounding conductor for this ungrounded system is correct according to NEC® 250.4(B)(2)?
- AAn equipment grounding conductor is not required for ungrounded systems.
- BThe equipment grounding conductor must be insulated and colored green.
- CThe equipment grounding conductor must be run with the circuit conductors.
- DThe equipment grounding conductor must be sized based on the system voltage.
Show answer & explanationAnswer & explanation
Correct answer: C. The equipment grounding conductor must be run with the circuit conductors.
NEC® 250.4(B)(2) states that for ungrounded systems, non-current-carrying metal parts of equipment and enclosures must be connected to an equipment grounding conductor. NEC® 250.134(B) further specifies that the equipment grounding conductor shall be run with the circuit conductors in the same raceway, cable, or trench. The system being ungrounded does not eliminate the need for equipment grounding.
Why the other options are wrong
- A. NEC® 250.4(B)(2) clearly states that non-current-carrying metal parts of equipment and enclosures must be connected to an equipment grounding conductor, even for ungrounded systems.
- B. While EGCs are often green, they are not always required to be insulated (e.g., bare copper) and their color is covered by NEC® 250.119, not the fundamental requirement for being run with circuit conductors.
- D. The EGC is sized based on the overcurrent protective device rating (NEC® 250.122), not primarily on system voltage.
EGC for Ungrounded Systems
Even ungrounded electrical systems require equipment grounding conductors to bond non-current-carrying metal parts to the system's grounding point, and these EGCs must be run with the circuit conductors to provide a low-impedance fault path.
- Required for ungrounded systems (NEC® 250.4(B)(2)).
- Must be run with circuit conductors (NEC® 250.134(B)).
- Provides a fault current path back to the source, even if not directly to earth at the service.
Memory trick: Ungrounded doesn't mean un-EGC'd; keep them together for safety's sake.