How many 350 kcmil THHN fit in 3" Flex?
5350 kcmil THHN/THWN-2 wires in 3" Flexible metal conduit (FMC, Greenfield)
7.069 sq in × 40 % = 2.8276 sq in allowed. ÷ 0.5242 sq in per wire = 5.39, so 5.
This pull in numbers
- 5 wires fill
- 37.1 % of 3" Flex
- Limit for three or more
- 40 %
- For 6 or more
- 3-1/2" Flex, up to 7
- Pipe to wire diameter
- 3.67 to 1
- In THW insulation
- 4 fit
- In XHHW-2 insulation
- 5 fit
Before you pull 5
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 5 is the total, not the hots.
- Derating. If all 5 were current-carrying, each would be adjusted to 80 % of its ampacity (Table 310.15(C)(1)): a 350 kcmil THHN at 350 A in the 90 °C column becomes 280 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.
350 kcmil THHN in other 3" conduit
| Conduit | Inside area | Most 350 kcmil THHN |
|---|---|---|
| Electrical metallic tubing | 8.846 | 6 |
| Intermediate metal conduit | 7.922 | 6 |
| Rigid metal conduit (RMC, GRC) | 7.499 | 5 |
| Rigid PVC conduit, Schedule 40 | 7.268 | 5 |
| Rigid PVC conduit, Schedule 80 | 6.442 | 5 |
| Flexible metal conduit (FMC, Greenfield) | 7.069 | 5 |
| Liquidtight flexible metal conduit (LFMC) | 7.475 | 5 |
350 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