How Many #8 THHN Fit in 3/4" PVC-40?
Maximum #8 THHN conductor count for 3/4" PVC-40 at the NEC 2023 40% fill cap (3 or more conductors).
In a 3/4" PVC-40, the NEC 2023 ceiling is 5 #8 THHN conductors. The code permits 40% of the conduit's 0.5080 in² interior to be filled when three or more conductors share the raceway (NEC Chapter 9, Table 1), which leaves 0.2032 in² of usable area; each #8 THHN takes 0.0366 in², so 0.2032 ÷ 0.0366 rounds down to 5. 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.
THE MATH IN ONE PASS
STEP UP OR STEP DOWN A SIZE
| Trade size | Area (in²) | 40% allowed (in²) | Max #8 THHN |
|---|---|---|---|
| 1/2" PVC-40 (smaller) | 0.2850 | 0.1140 | 3 |
| 3/4" PVC-40 ← | 0.5080 | 0.2032 | 5 |
| 1" PVC-40 (larger) | 0.8320 | 0.3328 | 9 |
All values per NEC 2023 · Chapter 9 · Tables 1, 4 and 5. THHN/THWN-2/XHHW share identical conductor area.
AT THE LIMIT
Why 5 is the ceiling — the 3/4" PVC-40 passes at 5 and fails at 6.
5 conductors = 36.0% fill (within the 40% cap); 6 would be 43.2% — over the limit.
TRY IT — CHANGE THE COUNT
Preloaded with this combination. Add conductors, switch insulation, or check a different trade size.
- CONDUCTORS
- 5
- WIRE AREA
- 0.183in²
- CONDUIT AREA
- 0.508in²
- JAM RISK
- LOW
- Three or more conductors — NEC allows 40% fill.