How many 350 kcmil THHN fit in 2-1/2" IMC?
4350 kcmil THHN/THWN-2 wires in 2-1/2" Intermediate metal conduit
5.135 sq in × 40 % = 2.0540 sq in allowed. ÷ 0.5242 sq in per wire = 3.92, which Note 7 rounds up to 4 because the decimal is 0.8 or more.
This pull in numbers
- 4 wires fill
- 40.8 % of 2-1/2" IMC
- Limit for three or more
- 40 %
- For 5 or more
- 3" IMC, up to 6
- Pipe to wire diameter
- 3.13 to 1
- In THW insulation
- 3 fit
- In XHHW-2 insulation
- 4 fit
The pipe is 3.13 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 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 2-1/2" conduit
| Conduit | Inside area | Most 350 kcmil THHN |
|---|---|---|
| Electrical metallic tubing | 5.858 | 4 |
| Intermediate metal conduit | 5.135 | 4 |
| Rigid metal conduit (RMC, GRC) | 4.866 | 3 |
| Rigid PVC conduit, Schedule 40 | 4.695 | 3 |
| Rigid PVC conduit, Schedule 80 | 4.119 | 3 |
| Flexible metal conduit (FMC, Greenfield) | 4.909 | 3 |
| Liquidtight flexible metal conduit (LFMC) | 4.881 | 3 |
350 kcmil THHN in other IMC sizes
Other wire sizes in 2-1/2" IMC
#12: 154#10: 97#8: 56#6: 40#4: 25#3: 21#2: 17#1: 13#1/0: 11#2/0: 9#3/0: 7#4/0: 6250 kcmil: 5300 kcmil: 4350 kcmil: 4500 kcmil: 3