How Many #10 THHN Fit in 1" PVC-40?

Maximum #10 THHN conductor count for 1" PVC-40 at the NEC 2023 40% fill cap (3 or more conductors).

In a 1" PVC-40, the NEC 2023 ceiling is 15 #10 THHN conductors. The code permits 40% of the conduit's 0.8320 in² interior to be filled when three or more conductors share the raceway (NEC Chapter 9, Table 1), which leaves 0.3328 in² of usable area; each #10 THHN takes 0.0211 in², so 0.3328 ÷ 0.0211 rounds down to 15. This is a fill limit, not an ampacity rating: every current-carrying conductor counts toward the total — including a neutral that carries current — and once more than three current-carrying conductors share the conduit you must also apply the ampacity adjustment factors in NEC 310.15(C)(1). THHN, THWN-2 and XHHW-2 share the same Table 5 cross-section, so the count is identical; RHH and RHW-2 are larger and fit fewer. On long or multi-bend pulls, plan pulling tension and lubricant even when the fill math says the conductors fit.