How many #4 THHN fit in 1" Flex?
44 AWG THHN/THWN-2 wires in 1" Flexible metal conduit (FMC, Greenfield)
0.817 sq in × 40 % = 0.3268 sq in allowed. ÷ 0.0824 sq in per wire = 3.97, which Note 7 rounds up to 4 because the decimal is 0.8 or more.
This pull in numbers
- 4 wires fill
- 40.3 % of 1" Flex
- Limit for three or more
- 40 %
- For 5 or more
- 1-1/4" Flex, up to 6
- Pipe to wire diameter
- 3.15 to 1
- In THW insulation
- 3 fit
- In XHHW-2 insulation
- 4 fit
The pipe is 3.15 times the wire's diameter, inside the 2.8 to 3.2 range where three wires can wedge side by side on a pull. If you pull exactly three, go up a size or pull with care.
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 #4 THHN at 95 A in the 90 °C column becomes 76 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.
#4 THHN in other 1" conduit
| Conduit | Inside area | Most #4 THHN |
|---|---|---|
| Electrical metallic tubing | 0.864 | 4 |
| Intermediate metal conduit | 0.959 | 4 |
| Rigid metal conduit (RMC, GRC) | 0.887 | 4 |
| Rigid PVC conduit, Schedule 40 | 0.832 | 4 |
| Rigid PVC conduit, Schedule 80 | 0.688 | 3 |
| Flexible metal conduit (FMC, Greenfield) | 0.817 | 4 |
| Liquidtight flexible metal conduit (LFMC) | 0.873 | 4 |
| Electrical nonmetallic tubing (smurf tube) | 0.832 | 4 |