How many #8 THHN fit in 1-1/2" IMC?
248 AWG THHN/THWN-2 wires in 1-1/2" Intermediate metal conduit
2.225 sq in × 40 % = 0.8900 sq in allowed. ÷ 0.0366 sq in per wire = 24.32, so 24.
This pull in numbers
- 24 wires fill
- 39.5 % of 1-1/2" IMC
- Limit for three or more
- 40 %
- For 25 or more
- 2" IMC, up to 39
- Pipe to wire diameter
- 7.79 to 1
- In THW insulation
- 20 fit
- In XHHW-2 insulation
- 20 fit
Before you pull 24
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 24 is the total, not the hots.
- Derating. If all 24 were current-carrying, each would be adjusted to 45 % of its ampacity (Table 310.15(C)(1)): a #8 THHN at 55 A in the 90 °C column becomes 24.8 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.
#8 THHN in other 1-1/2" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 2.036 | 22 |
| Intermediate metal conduit | 2.225 | 24 |
| Rigid metal conduit (RMC, GRC) | 2.071 | 22 |
| Rigid PVC conduit, Schedule 40 | 1.986 | 21 |
| Rigid PVC conduit, Schedule 80 | 1.711 | 18 |
| Flexible metal conduit (FMC, Greenfield) | 1.858 | 20 |
| Liquidtight flexible metal conduit (LFMC) | 1.981 | 21 |
| Electrical nonmetallic tubing (smurf tube) | 1.986 | 21 |
#8 THHN in other IMC sizes
Other wire sizes in 1-1/2" IMC
#14: 91#12: 67#10: 42#8: 24#6: 17#4: 11#3: 9#2: 7#1: 5#1/0: 4#2/0: 4#3/0: 3#4/0: 2250 kcmil: 1300 kcmil: 1350 kcmil: 1500 kcmil: 1