How many 250 kcmil THHN fit in 4" Flex?
12250 kcmil THHN/THWN-2 wires in 4" Flexible metal conduit (FMC, Greenfield)
12.566 sq in × 40 % = 5.0264 sq in allowed. ÷ 0.3970 sq in per wire = 12.66, so 12.
This pull in numbers
- 12 wires fill
- 37.9 % of 4" Flex
- Limit for three or more
- 40 %
- For 13 or more
- no bigger Flex
- Pipe to wire diameter
- 5.63 to 1
- In THW insulation
- 11 fit
- In XHHW-2 insulation
- 13 fit
Before you pull 12
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 12 is the total, not the hots.
- Derating. If all 12 were current-carrying, each would be adjusted to 50 % of its ampacity (Table 310.15(C)(1)): a 250 kcmil THHN at 290 A in the 90 °C column becomes 145 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.
250 kcmil THHN in other 4" conduit
| Conduit | Inside area | Most 250 kcmil THHN |
|---|---|---|
| Electrical metallic tubing | 14.753 | 15 |
| Intermediate metal conduit | 13.631 | 13 |
| Rigid metal conduit (RMC, GRC) | 12.882 | 13 |
| Rigid PVC conduit, Schedule 40 | 12.554 | 12 |
| Rigid PVC conduit, Schedule 80 | 11.258 | 11 |
| Flexible metal conduit (FMC, Greenfield) | 12.566 | 12 |
| Liquidtight flexible metal conduit (LFMC) | 12.692 | 12 |
250 kcmil 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