CSLB C-10 Electrical ContractorWiring Methods and MaterialsHard
An 8-foot length of flexible metal conduit (FMC) is used to connect to a vibrating pump motor on a 20A branch circuit. No separate equipment grounding conductor is installed inside the FMC. Does this installation comply with NEC requirements for using the conduit as the equipment ground path?
- ANo, because FMC can only serve as the equipment ground path when the total length in the ground path does not exceed 6 feet
- BYes, FMC may always serve as the sole equipment grounding path regardless of length
- CYes, because the circuit is rated 20A or less, which permits any length of FMC as the ground path
- DNo, because FMC is never permitted to serve as an equipment grounding conductor
Show answer & explanationAnswer & explanation
Correct answer: A. No, because FMC can only serve as the equipment ground path when the total length in the ground path does not exceed 6 feet
Per NEC 250.118(6), flexible metal conduit is permitted to serve as an equipment grounding conductor only where the circuit is protected at 20 amperes or less AND the total length of FMC in the ground return path does not exceed 6 feet. Since this run is 8 feet, a separate equipment grounding conductor must be installed.
Why the other options are wrong
- B. Length is a specific limiting factor; FMC cannot always serve as the sole ground path.
- C. The 20A rating alone is not sufficient; the 6-foot length limit must also be met.
- D. FMC can serve as an EGC under specific conditions, so it is not universally prohibited.
FMC as Equipment Grounding Conductor
NEC 250.118(6) allows flexible metal conduit to serve as an equipment grounding conductor only if the circuit is 20A or less and the FMC length does not exceed 6 feet.
- Both conditions (20A circuit AND 6 ft length) must be met.
- Exceeding either condition requires a separate EGC.
- Applies specifically to FMC, not LFMC (which has its own separate rule).
Memory trick: 'Six feet and twenty amps' — the FMC ground path double limit.