How many 250 kcmil THHN fit in 3" Flex?
7250 kcmil THHN/THWN-2 wires in 3" Flexible metal conduit (FMC, Greenfield)
7.069 sq in × 40 % = 2.8276 sq in allowed. ÷ 0.3970 sq in per wire = 7.12, so 7.
This pull in numbers
- 7 wires fill
- 39.3 % of 3" Flex
- Limit for three or more
- 40 %
- For 8 or more
- 3-1/2" Flex, up to 9
- Pipe to wire diameter
- 4.22 to 1
- In THW insulation
- 6 fit
- In XHHW-2 insulation
- 7 fit
Before you pull 7
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 7 is the total, not the hots.
- Derating. If all 7 were current-carrying, each would be adjusted to 70 % of its ampacity (Table 310.15(C)(1)): a 250 kcmil THHN at 290 A in the 90 °C column becomes 203 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 3" conduit
| Conduit | Inside area | Most 250 kcmil THHN |
|---|---|---|
| Electrical metallic tubing | 8.846 | 9 |
| Intermediate metal conduit | 7.922 | 8 |
| Rigid metal conduit (RMC, GRC) | 7.499 | 7 |
| Rigid PVC conduit, Schedule 40 | 7.268 | 7 |
| Rigid PVC conduit, Schedule 80 | 6.442 | 6 |
| Flexible metal conduit (FMC, Greenfield) | 7.069 | 7 |
| Liquidtight flexible metal conduit (LFMC) | 7.475 | 7 |
250 kcmil 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