How many #8 THHN fit in 1" IMC?
108 AWG THHN/THWN-2 wires in 1" Intermediate metal conduit
0.959 sq in × 40 % = 0.3836 sq in allowed. ÷ 0.0366 sq in per wire = 10.48, so 10.
This pull in numbers
- 10 wires fill
- 38.2 % of 1" IMC
- Limit for three or more
- 40 %
- For 11 or more
- 1-1/4" IMC, up to 18
- Pipe to wire diameter
- 5.12 to 1
- In THW insulation
- 8 fit
- In XHHW-2 insulation
- 8 fit
Before you pull 10
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 10 is the total, not the hots.
- Derating. If all 10 were current-carrying, each would be adjusted to 50 % of its ampacity (Table 310.15(C)(1)): a #8 THHN at 55 A in the 90 °C column becomes 27.5 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 1" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 0.864 | 9 |
| Intermediate metal conduit | 0.959 | 10 |
| Rigid metal conduit (RMC, GRC) | 0.887 | 9 |
| Rigid PVC conduit, Schedule 40 | 0.832 | 9 |
| Rigid PVC conduit, Schedule 80 | 0.688 | 7 |
| Flexible metal conduit (FMC, Greenfield) | 0.817 | 9 |
| Liquidtight flexible metal conduit (LFMC) | 0.873 | 9 |
| Electrical nonmetallic tubing (smurf tube) | 0.832 | 9 |
#8 THHN in other IMC sizes
Other wire sizes in 1" IMC
#14: 39#12: 29#10: 18#8: 10#6: 7#4: 4#3: 4#2: 3#1: 1#1/0: 1#2/0: 1#3/0: 1#4/0: 1250 kcmil: 1300 kcmil: 1