CSLB C-10 Electrical ContractorPlanning and EstimatingMedium
A contractor is preparing a material takeoff for a new commercial retail space. The plans indicate the use of flexible metal conduit (FMC) for connecting several recessed lighting fixtures to a junction box. The circuit will use three 12 AWG THHN conductors. What is the maximum number of 12 AWG THHN conductors permitted in a 3/8-inch trade size FMC, assuming all conductors are current-carrying?
- A4
- B6
- C3
- D5
Show answer & explanationAnswer & explanation
Correct answer: A. 4
According to NEC Annex C, Table C.5 (FMC), a 3/8-inch trade size flexible metal conduit can accommodate a maximum of four 12 AWG THHN conductors.
Why the other options are wrong
- B. 6 conductors is significantly over the limit for 12 AWG THHN in 3/8-inch FMC.
- C. 3 conductors is below the maximum allowed for 12 AWG THHN in 3/8-inch FMC.
- D. 5 conductors would exceed the allowable fill for 12 AWG THHN in 3/8-inch FMC.
Flexible Metal Conduit (FMC) Fill
The maximum number of conductors allowed within Flexible Metal Conduit (FMC) based on conductor size, insulation type, and conduit trade size, specified in NEC Annex C.
- FMC is often used for short, flexible connections to equipment or lighting.
- Due to its flexible nature, FMC's internal dimensions can vary slightly, so Annex C tables are critical.
- The insulation type of the conductors significantly impacts the conductor area and thus the fill.
Memory trick: FMC fill: 'Flexible' 'Means' 'Careful' 'Counts' from the 'Table'.