How many #8 THHN fit in 3/4" Flex?
68 AWG THHN/THWN-2 wires in 3/4" Flexible metal conduit (FMC, Greenfield)
0.533 sq in × 40 % = 0.2132 sq in allowed. ÷ 0.0366 sq in per wire = 5.83, which Note 7 rounds up to 6 because the decimal is 0.8 or more.
This pull in numbers
- 6 wires fill
- 41.2 % of 3/4" Flex
- Limit for three or more
- 40 %
- For 7 or more
- 1" Flex, up to 9
- Pipe to wire diameter
- 3.81 to 1
- In THW insulation
- 5 fit
- In XHHW-2 insulation
- 5 fit
Before you pull 6
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 6 is the total, not the hots.
- Derating. If all 6 were current-carrying, each would be adjusted to 80 % of its ampacity (Table 310.15(C)(1)): a #8 THHN at 55 A in the 90 °C column becomes 44 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.
#8 THHN in other 3/4" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 0.533 | 6 |
| Intermediate metal conduit | 0.586 | 6 |
| Rigid metal conduit (RMC, GRC) | 0.549 | 6 |
| Rigid PVC conduit, Schedule 40 | 0.508 | 5 |
| Rigid PVC conduit, Schedule 80 | 0.409 | 4 |
| Flexible metal conduit (FMC, Greenfield) | 0.533 | 6 |
| Liquidtight flexible metal conduit (LFMC) | 0.541 | 6 |
| Electrical nonmetallic tubing (smurf tube) | 0.508 | 5 |