How many #14 THHN fit in 3/8" Flex?
414 AWG THHN/THWN-2 wires in 3/8" Flexible metal conduit (FMC, Greenfield)
0.116 sq in × 40 % = 0.0464 sq in allowed. ÷ 0.0097 sq in per wire = 4.78, so 4.
This pull in numbers
- 4 wires fill
- 33.4 % of 3/8" Flex
- Limit for three or more
- 40 %
- For 5 or more
- 1/2" Flex, up to 13
- Pipe to wire diameter
- 3.46 to 1
- In THW insulation
- 3 fit
- In XHHW-2 insulation
- 3 fit
Before you pull 4
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 4 is the total, not the hots.
- Derating. If all 4 were current-carrying, each would be adjusted to 80 % of its ampacity (Table 310.15(C)(1)): a #14 THHN at 25 A in the 90 °C column becomes 20 A. Grounds don't count as current-carrying. How derating works
- Bends. A full pipe pulls hard. Keep to 360° of bends between pull points, less for a tight fill.
#14 THHN in other 3/8" conduit
| Conduit | Inside area | Most #14 THHN |
|---|---|---|
| Flexible metal conduit (FMC, Greenfield) | 0.116 | 4 |
| Liquidtight flexible metal conduit (LFMC) | 0.192 | 8 |