How many #8 THHN fit in 4" Flex?
1378 AWG THHN/THWN-2 wires in 4" Flexible metal conduit (FMC, Greenfield)
12.566 sq in × 40 % = 5.0264 sq in allowed. ÷ 0.0366 sq in per wire = 137.33, so 137.
This pull in numbers
- 137 wires fill
- 39.9 % of 4" Flex
- Limit for three or more
- 40 %
- For 138 or more
- no bigger Flex
- Pipe to wire diameter
- 18.52 to 1
- In THW insulation
- 115 fit
- In XHHW-2 insulation
- 115 fit
Before you pull 137
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 137 is the total, not the hots.
- Derating. If all 137 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 4" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 14.753 | 161 |
| Intermediate metal conduit | 13.631 | 149 |
| Rigid metal conduit (RMC, GRC) | 12.882 | 140 |
| Rigid PVC conduit, Schedule 40 | 12.554 | 137 |
| Rigid PVC conduit, Schedule 80 | 11.258 | 123 |
| Flexible metal conduit (FMC, Greenfield) | 12.566 | 137 |
| Liquidtight flexible metal conduit (LFMC) | 12.692 | 138 |
#8 THHN in other Flex sizes
Other wire sizes in 4" Flex
#8: 137#6: 99#4: 61#3: 51#2: 43#1: 32#1/0: 27#2/0: 22#3/0: 18#4/0: 15250 kcmil: 12300 kcmil: 11350 kcmil: 9500 kcmil: 7