How many 300 kcmil THHN fit in 2-1/2" Flex?
4300 kcmil THHN/THWN-2 wires in 2-1/2" Flexible metal conduit (FMC, Greenfield)
4.909 sq in × 40 % = 1.9636 sq in allowed. ÷ 0.4608 sq in per wire = 4.26, so 4.
This pull in numbers
- 4 wires fill
- 37.5 % of 2-1/2" Flex
- Limit for three or more
- 40 %
- For 5 or more
- 3" Flex, up to 6
- Pipe to wire diameter
- 3.26 to 1
- In THW insulation
- 3 fit
- In XHHW-2 insulation
- 4 fit
Before you pull 4
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 4 is the total, not the hots.
- Derating. If all 4 were current-carrying, each would be adjusted to 80 % of its ampacity (Table 310.15(C)(1)): a 300 kcmil THHN at 320 A in the 90 °C column becomes 256 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.
300 kcmil THHN in other 2-1/2" conduit
| Conduit | Inside area | Most 300 kcmil THHN |
|---|---|---|
| Electrical metallic tubing | 5.858 | 5 |
| Intermediate metal conduit | 5.135 | 4 |
| Rigid metal conduit (RMC, GRC) | 4.866 | 4 |
| Rigid PVC conduit, Schedule 40 | 4.695 | 4 |
| Rigid PVC conduit, Schedule 80 | 4.119 | 3 |
| Flexible metal conduit (FMC, Greenfield) | 4.909 | 4 |
| Liquidtight flexible metal conduit (LFMC) | 4.881 | 4 |
300 kcmil 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