How Many #8 Wires Can I Fit in 1 1/4 Inch Schedule 40 PVC?

A user asked the app how many #8 conductors fit in 1 1/4 inch Schedule 40 PVC. For 8 AWG THHN or THWN, NEC 2023 Informative Annex C, Table C.10 says fifteen conductors. If you want to verify by hand, a #8 THHN occupies 0.0366 square inches, the 40 percent fill of 1 1/4 inch Schedule 40 is 0.581 square inches, and 0.581 divided by 0.0366 gives 15.8, which truncates to 15.

Insulation type moves the number

The count is only valid for the insulation you actually pull. 8 AWG THW is fatter at 0.0556 square inches, which drops the count to ten. XHHW lands at 0.0437 for thirteen. Bare grounds calculate at their Table 8 area of 0.017 square inches. Never mix table answers with a mixed pull; when conductor sizes or types differ, you must do the Table 4 and Table 5 math conductor by conductor instead of using Annex C.

Fifteen fit, but fifteen rarely work

Ampacity adjustment under 310.15(C)(1) is where big counts fall apart. From the 90 degree column, 8 AWG THHN starts at 55 amps. With 10 to 20 current carrying conductors in the raceway, ampacity drops to 50 percent, leaving 27.5 amps, which no longer supports a 40 amp circuit and barely covers 30. Nine current carrying conductors at 70 percent keep 38.5 amps, enough for a 35 amp breaker or a 40 with the next size up rule in 240.4(B) when the load allows. If those #8s feed 40 amp loads like water heaters or mini splits, three circuits per pipe is the practical ceiling.

Underground bonus considerations

Schedule 40 in a trench must be THWN rated conductors because 300.5(B) treats the interior of underground raceways as a wet location. Most dual rated THHN/THWN-2 wire covers this automatically, but check the jacket print before the pull.

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