How many #8 THHN fit in 2-1/2" IMC?
568 AWG THHN/THWN-2 wires in 2-1/2" Intermediate metal conduit
5.135 sq in × 40 % = 2.0540 sq in allowed. ÷ 0.0366 sq in per wire = 56.12, so 56.
This pull in numbers
- 56 wires fill
- 39.9 % of 2-1/2" IMC
- Limit for three or more
- 40 %
- For 57 or more
- 3" IMC, up to 86
- Pipe to wire diameter
- 11.84 to 1
- In THW insulation
- 47 fit
- In XHHW-2 insulation
- 47 fit
Before you pull 56
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 56 is the total, not the hots.
- Derating. If all 56 were current-carrying, each would be adjusted to 35 % of its ampacity (Table 310.15(C)(1)): a #8 THHN at 55 A in the 90 °C column becomes 19.3 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.
#8 THHN in other 2-1/2" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 5.858 | 64 |
| Intermediate metal conduit | 5.135 | 56 |
| Rigid metal conduit (RMC, GRC) | 4.866 | 53 |
| Rigid PVC conduit, Schedule 40 | 4.695 | 51 |
| Rigid PVC conduit, Schedule 80 | 4.119 | 45 |
| Flexible metal conduit (FMC, Greenfield) | 4.909 | 53 |
| Liquidtight flexible metal conduit (LFMC) | 4.881 | 53 |
#8 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