How many 500 kcmil THHN fit in 3" Flex?
4500 kcmil THHN/THWN-2 wires in 3" Flexible metal conduit (FMC, Greenfield)
7.069 sq in × 40 % = 2.8276 sq in allowed. ÷ 0.7073 sq in per wire = 4.00, which Note 7 rounds up to 4 because the decimal is 0.8 or more.
This pull in numbers
- 4 wires fill
- 40.0 % of 3" Flex
- Limit for three or more
- 40 %
- For 5 or more
- 3-1/2" Flex, up to 5
- Pipe to wire diameter
- 3.16 to 1
- In THW insulation
- 3 fit
- In XHHW-2 insulation
- 4 fit
The pipe is 3.16 times the wire's diameter, inside the 2.8 to 3.2 range where three wires can wedge side by side on a pull. If you pull exactly three, go up a size or pull with care.
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 500 kcmil THHN at 430 A in the 90 °C column becomes 344 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.
500 kcmil THHN in other 3" conduit
| Conduit | Inside area | Most 500 kcmil THHN |
|---|---|---|
| Electrical metallic tubing | 8.846 | 5 |
| Intermediate metal conduit | 7.922 | 4 |
| Rigid metal conduit (RMC, GRC) | 7.499 | 4 |
| Rigid PVC conduit, Schedule 40 | 7.268 | 4 |
| Rigid PVC conduit, Schedule 80 | 6.442 | 3 |
| Flexible metal conduit (FMC, Greenfield) | 7.069 | 4 |
| Liquidtight flexible metal conduit (LFMC) | 7.475 | 4 |
500 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