Journeyman Electrician Exam (NEC)Wiring Methods and MaterialsHard
A commercial building requires a new 208-volt, 3-phase, 60-amp feeder circuit to a subpanel using individual 6 AWG THHN copper conductors in a flexible metal conduit (FMC). The FMC will be used as the equipment grounding conductor. What is the maximum length of FMC permitted to serve as the equipment grounding conductor for this circuit, according to NEC 250.118(5)?
- A4 feet
- B5 feet
- C3 feet
- D6 feet
Show answer & explanationAnswer & explanation
Correct answer: D. 6 feet
NEC 250.118(5) permits flexible metal conduit (FMC) to be used as an equipment grounding conductor if the conduit and fittings are listed for grounding, the circuit conductors contained therein are protected by overcurrent devices rated at 20 amperes or less, AND the combined length of the FMC in the ground return path does not exceed 6 feet. For circuits over 20A, a separate EGC is required.
Why the other options are wrong
- A. Incorrect. This is less than the maximum permitted length for FMC to serve as an EGC.
- B. Incorrect. This is less than the maximum permitted length for FMC to serve as an EGC.
- C. Incorrect. This is less than the maximum permitted length for FMC to serve as an EGC.
FMC as EGC Limitations
Flexible Metal Conduit (FMC) can serve as an equipment grounding conductor only under specific conditions, including limitations on circuit amperage and the maximum length of the conduit run.
- NEC 250.118 lists acceptable equipment grounding conductors.
- FMC can be an EGC if listed for grounding, and the circuit's OCPD is 20A or less, AND the FMC length is 6 feet or less.
- Exceptions exist for larger FMC (1-1/4 inch or larger) with OCPD up to 60A.
- A separate EGC is generally required if these conditions are not met.
Memory trick: Six feet for flex, or a separate ground annex!