How many #8 THHN fit in 2-1/2" PVC Sch 40?
518 AWG THHN/THWN-2 wires in 2-1/2" Rigid PVC conduit, Schedule 40
4.695 sq in × 40 % = 1.8780 sq in allowed. ÷ 0.0366 sq in per wire = 51.31, so 51.
This pull in numbers
- 51 wires fill
- 39.8 % of 2-1/2" PVC Sch 40
- Limit for three or more
- 40 %
- For 52 or more
- 3" PVC Sch 40, up to 79
- Pipe to wire diameter
- 11.32 to 1
- In THW insulation
- 43 fit
- In XHHW-2 insulation
- 43 fit
Before you pull 51
- The ground counts. Every wire in the pipe counts toward fill, the green or bare ground and the neutrals too. 51 is the total, not the hots.
- Derating. If all 51 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 2-1/2" conduit
| Conduit | Inside area | Most #8 THHN |
|---|---|---|
| Electrical metallic tubing | 5.858 | 64 |
| Intermediate metal conduit | 5.135 | 56 |
| Rigid metal conduit (RMC, GRC) | 4.866 | 53 |
| Rigid PVC conduit, Schedule 40 | 4.695 | 51 |
| Rigid PVC conduit, Schedule 80 | 4.119 | 45 |
| Flexible metal conduit (FMC, Greenfield) | 4.909 | 53 |
| Liquidtight flexible metal conduit (LFMC) | 4.881 | 53 |
#8 THHN in other PVC Sch 40 sizes
Other wire sizes in 2-1/2" PVC Sch 40
#14: 193#12: 141#10: 89#8: 51#6: 37#4: 22#3: 19#2: 16#1: 12#1/0: 10#2/0: 8#3/0: 7#4/0: 6250 kcmil: 4300 kcmil: 4350 kcmil: 3500 kcmil: 2