How many #8 THHN fit in 3" Rigid?
828 AWG THHN/THWN-2 wires in 3" Rigid metal conduit (RMC, GRC)
7.499 sq in × 40 % = 2.9996 sq in allowed. ÷ 0.0366 sq in per wire = 81.96, which Note 7 rounds up to 82 because the decimal is 0.8 or more.
This pull in numbers
- 82 wires fill
- 40.0 % of 3" Rigid
- Limit for three or more
- 40 %
- For 83 or more
- 3-1/2" Rigid, up to 109
- Pipe to wire diameter
- 14.31 to 1
- In THW insulation
- 68 fit
- In XHHW-2 insulation
- 68 fit
Before you pull 82
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 82 is the total, not the hots.
- Derating. If all 82 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" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 8.846 | 96 |
| Intermediate metal conduit | 7.922 | 86 |
| Rigid metal conduit (RMC, GRC) | 7.499 | 82 |
| Rigid PVC conduit, Schedule 40 | 7.268 | 79 |
| Rigid PVC conduit, Schedule 80 | 6.442 | 70 |
| Flexible metal conduit (FMC, Greenfield) | 7.069 | 77 |
| Liquidtight flexible metal conduit (LFMC) | 7.475 | 81 |
#8 THHN in other Rigid sizes
Other wire sizes in 3" Rigid
#10: 142#8: 82#6: 59#4: 36#3: 31#2: 26#1: 19#1/0: 16#2/0: 13#3/0: 11#4/0: 9250 kcmil: 7300 kcmil: 6350 kcmil: 5500 kcmil: 4