How many #8 THHN fit in 3-1/2" Rigid?
1098 AWG THHN/THWN-2 wires in 3-1/2" Rigid metal conduit (RMC, GRC)
10.010 sq in × 40 % = 4.0040 sq in allowed. ÷ 0.0366 sq in per wire = 109.40, so 109.
This pull in numbers
- 109 wires fill
- 39.9 % of 3-1/2" Rigid
- Limit for three or more
- 40 %
- For 110 or more
- 4" Rigid, up to 140
- Pipe to wire diameter
- 16.53 to 1
- In THW insulation
- 91 fit
- In XHHW-2 insulation
- 91 fit
Before you pull 109
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 109 is the total, not the hots.
- Derating. If all 109 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 Rigid sizes
Other wire sizes in 3-1/2" Rigid
#10: 189#8: 109#6: 79#4: 48#3: 41#2: 34#1: 25#1/0: 21#2/0: 18#3/0: 15#4/0: 12250 kcmil: 10300 kcmil: 8350 kcmil: 7500 kcmil: 5