How many 300 kcmil THHN fit in 3-1/2" Flex?
8300 kcmil THHN/THWN-2 wires in 3-1/2" Flexible metal conduit (FMC, Greenfield)
9.621 sq in × 40 % = 3.8484 sq in allowed. ÷ 0.4608 sq in per wire = 8.35, so 8.
This pull in numbers
- 8 wires fill
- 38.3 % of 3-1/2" Flex
- Limit for three or more
- 40 %
- For 9 or more
- 4" Flex, up to 11
- Pipe to wire diameter
- 4.57 to 1
- In THW insulation
- 7 fit
- In XHHW-2 insulation
- 8 fit
Before you pull 8
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 8 is the total, not the hots.
- Derating. If all 8 were current-carrying, each would be adjusted to 70 % of its ampacity (Table 310.15(C)(1)): a 300 kcmil THHN at 320 A in the 90 °C column becomes 224 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 3-1/2" conduit
| Conduit | Inside area | Most 300 kcmil THHN |
|---|---|---|
| Electrical metallic tubing | 11.545 | 10 |
| Intermediate metal conduit | 10.584 | 9 |
| Rigid metal conduit (RMC, GRC) | 10.010 | 8 |
| Rigid PVC conduit, Schedule 40 | 9.737 | 8 |
| Rigid PVC conduit, Schedule 80 | 8.688 | 7 |
| Flexible metal conduit (FMC, Greenfield) | 9.621 | 8 |
| Liquidtight flexible metal conduit (LFMC) | 9.731 | 8 |
300 kcmil THHN in other Flex sizes
Other wire sizes in 3-1/2" Flex
#10: 182#8: 105#6: 76#4: 46#3: 39#2: 33#1: 24#1/0: 20#2/0: 17#3/0: 14#4/0: 12250 kcmil: 9300 kcmil: 8350 kcmil: 7500 kcmil: 5