How many #8 THHN fit in 3" Flex?
778 AWG THHN/THWN-2 wires in 3" Flexible metal conduit (FMC, Greenfield)
7.069 sq in × 40 % = 2.8276 sq in allowed. ÷ 0.0366 sq in per wire = 77.26, so 77.
This pull in numbers
- 77 wires fill
- 39.9 % of 3" Flex
- Limit for three or more
- 40 %
- For 78 or more
- 3-1/2" Flex, up to 105
- Pipe to wire diameter
- 13.89 to 1
- In THW insulation
- 64 fit
- In XHHW-2 insulation
- 64 fit
Before you pull 77
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 77 is the total, not the hots.
- Derating. If all 77 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 3" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 8.846 | 96 |
| Intermediate metal conduit | 7.922 | 86 |
| Rigid metal conduit (RMC, GRC) | 7.499 | 82 |
| Rigid PVC conduit, Schedule 40 | 7.268 | 79 |
| Rigid PVC conduit, Schedule 80 | 6.442 | 70 |
| Flexible metal conduit (FMC, Greenfield) | 7.069 | 77 |
| Liquidtight flexible metal conduit (LFMC) | 7.475 | 81 |
#8 THHN in other Flex sizes
Other wire sizes in 3" Flex
#10: 134#8: 77#6: 55#4: 34#3: 29#2: 24#1: 18#1/0: 15#2/0: 12#3/0: 10#4/0: 8250 kcmil: 7300 kcmil: 6350 kcmil: 5500 kcmil: 4