How many #8 THHN fit in 2-1/2" Flex?
538 AWG THHN/THWN-2 wires in 2-1/2" Flexible metal conduit (FMC, Greenfield)
4.909 sq in × 40 % = 1.9636 sq in allowed. ÷ 0.0366 sq in per wire = 53.65, so 53.
This pull in numbers
- 53 wires fill
- 39.5 % of 2-1/2" Flex
- Limit for three or more
- 40 %
- For 54 or more
- 3" Flex, up to 77
- Pipe to wire diameter
- 11.57 to 1
- In THW insulation
- 45 fit
- In XHHW-2 insulation
- 45 fit
Before you pull 53
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 53 is the total, not the hots.
- Derating. If all 53 were current-carrying, each would be adjusted to 35 % of its ampacity (Table 310.15(C)(1)): a #8 THHN at 55 A in the 90 °C column becomes 19.3 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 2-1/2" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 5.858 | 64 |
| Intermediate metal conduit | 5.135 | 56 |
| Rigid metal conduit (RMC, GRC) | 4.866 | 53 |
| Rigid PVC conduit, Schedule 40 | 4.695 | 51 |
| Rigid PVC conduit, Schedule 80 | 4.119 | 45 |
| Flexible metal conduit (FMC, Greenfield) | 4.909 | 53 |
| Liquidtight flexible metal conduit (LFMC) | 4.881 | 53 |
#8 THHN in other Flex sizes
Other wire sizes in 2-1/2" Flex
#12: 147#10: 93#8: 53#6: 38#4: 24#3: 20#2: 17#1: 12#1/0: 10#2/0: 9#3/0: 7#4/0: 6250 kcmil: 5300 kcmil: 4350 kcmil: 3500 kcmil: 2