How many #8 THHN fit in 3" IMC?
868 AWG THHN/THWN-2 wires in 3" Intermediate metal conduit
7.922 sq in × 40 % = 3.1688 sq in allowed. ÷ 0.0366 sq in per wire = 86.58, so 86.
This pull in numbers
- 86 wires fill
- 39.7 % of 3" IMC
- Limit for three or more
- 40 %
- For 87 or more
- 3-1/2" IMC, up to 115
- Pipe to wire diameter
- 14.70 to 1
- In THW insulation
- 72 fit
- In XHHW-2 insulation
- 72 fit
Before you pull 86
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 86 is the total, not the hots.
- Derating. If all 86 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 3" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 8.846 | 96 |
| Intermediate metal conduit | 7.922 | 86 |
| Rigid metal conduit (RMC, GRC) | 7.499 | 82 |
| Rigid PVC conduit, Schedule 40 | 7.268 | 79 |
| Rigid PVC conduit, Schedule 80 | 6.442 | 70 |
| Flexible metal conduit (FMC, Greenfield) | 7.069 | 77 |
| Liquidtight flexible metal conduit (LFMC) | 7.475 | 81 |
#8 THHN in other IMC sizes
Other wire sizes in 3" IMC
#10: 150#8: 86#6: 62#4: 38#3: 32#2: 27#1: 20#1/0: 17#2/0: 14#3/0: 12#4/0: 9250 kcmil: 8300 kcmil: 7350 kcmil: 6500 kcmil: 4