How many #8 THHN fit in 3-1/2" IMC?
1158 AWG THHN/THWN-2 wires in 3-1/2" Intermediate metal conduit
10.584 sq in × 40 % = 4.2336 sq in allowed. ÷ 0.0366 sq in per wire = 115.67, so 115.
This pull in numbers
- 115 wires fill
- 39.8 % of 3-1/2" IMC
- Limit for three or more
- 40 %
- For 116 or more
- 4" IMC, up to 149
- Pipe to wire diameter
- 17.00 to 1
- In THW insulation
- 97 fit
- In XHHW-2 insulation
- 97 fit
Before you pull 115
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 115 is the total, not the hots.
- Derating. If all 115 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 3-1/2" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 11.545 | 126 |
| Intermediate metal conduit | 10.584 | 115 |
| Rigid metal conduit (RMC, GRC) | 10.010 | 109 |
| Rigid PVC conduit, Schedule 40 | 9.737 | 106 |
| Rigid PVC conduit, Schedule 80 | 8.688 | 95 |
| Flexible metal conduit (FMC, Greenfield) | 9.621 | 105 |
| Liquidtight flexible metal conduit (LFMC) | 9.731 | 106 |
#8 THHN in other IMC sizes
Other wire sizes in 3-1/2" IMC
#10: 200#8: 115#6: 83#4: 51#3: 43#2: 36#1: 27#1/0: 23#2/0: 19#3/0: 16#4/0: 13250 kcmil: 10300 kcmil: 9350 kcmil: 8500 kcmil: 6