How many #4 THHN fit in 2-1/2" IMC?
254 AWG THHN/THWN-2 wires in 2-1/2" Intermediate metal conduit
5.135 sq in × 40 % = 2.0540 sq in allowed. ÷ 0.0824 sq in per wire = 24.93, which Note 7 rounds up to 25 because the decimal is 0.8 or more.
This pull in numbers
- 25 wires fill
- 40.1 % of 2-1/2" IMC
- Limit for three or more
- 40 %
- For 26 or more
- 3" IMC, up to 38
- Pipe to wire diameter
- 7.89 to 1
- In THW insulation
- 21 fit
- In XHHW-2 insulation
- 25 fit
Before you pull 25
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 25 is the total, not the hots.
- Derating. If all 25 were current-carrying, each would be adjusted to 45 % of its ampacity (Table 310.15(C)(1)): a #4 THHN at 95 A in the 90 °C column becomes 42.8 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.
#4 THHN in other 2-1/2" conduit
| Conduit | Inside area | Most #4 THHN |
|---|---|---|
| Electrical metallic tubing | 5.858 | 28 |
| Intermediate metal conduit | 5.135 | 25 |
| Rigid metal conduit (RMC, GRC) | 4.866 | 23 |
| Rigid PVC conduit, Schedule 40 | 4.695 | 22 |
| Rigid PVC conduit, Schedule 80 | 4.119 | 20 |
| Flexible metal conduit (FMC, Greenfield) | 4.909 | 24 |
| Liquidtight flexible metal conduit (LFMC) | 4.881 | 23 |
#4 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