How many #8 THHN fit in 1-1/4" IMC?
188 AWG THHN/THWN-2 wires in 1-1/4" Intermediate metal conduit
1.647 sq in × 40 % = 0.6588 sq in allowed. ÷ 0.0366 sq in per wire = 18.00, so 18.
This pull in numbers
- 18 wires fill
- 40.0 % of 1-1/4" IMC
- Limit for three or more
- 40 %
- For 19 or more
- 1-1/2" IMC, up to 24
- Pipe to wire diameter
- 6.70 to 1
- In THW insulation
- 15 fit
- In XHHW-2 insulation
- 15 fit
Before you pull 18
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 18 is the total, not the hots.
- Derating. If all 18 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 1-1/4" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 1.496 | 16 |
| Intermediate metal conduit | 1.647 | 18 |
| Rigid metal conduit (RMC, GRC) | 1.526 | 16 |
| Rigid PVC conduit, Schedule 40 | 1.453 | 16 |
| Rigid PVC conduit, Schedule 80 | 1.237 | 13 |
| Flexible metal conduit (FMC, Greenfield) | 1.277 | 14 |
| Liquidtight flexible metal conduit (LFMC) | 1.528 | 16 |
| Electrical nonmetallic tubing (smurf tube) | 1.453 | 16 |
#8 THHN in other IMC sizes
Other wire sizes in 1-1/4" IMC
#14: 68#12: 49#10: 31#8: 18#6: 13#4: 8#3: 6#2: 5#1: 4#1/0: 3#2/0: 3#3/0: 1#4/0: 1250 kcmil: 1300 kcmil: 1350 kcmil: 1500 kcmil: 1