Read the equipment markings
Use the lowest applicable termination rating at the connected equipment. Do not select 75°C or 90°C simply because the wire insulation carries that rating. The equipment listing and NEC 110.14(C) determine which column can be used.
Adjust the wire, then check the ceiling
For supported dual-rated THHN/THWN-2, PassPull starts with the 90°C ampacity for adjustment and correction, then caps the result at the selected terminal column.
With six current-carrying #10 copper conductors at 30°C, the adjusted figure is 40 A × 80% = 32 A. A verified 75°C terminal column allows 35 A, so 32 A controls. With a 60°C terminal column, 30 A controls instead. Ordinary small-wire protection remains a separate check.
| Verified terminal rating | Terminal-column limit | Ampacity after adjustment and cap |
|---|---|---|
| 60°C | 30 A | 30 A |
| 75°C | 35 A | 32 A |
| 90°C | 40 A | 32 A |
Does 90°C insulation allow a larger breaker?
The insulation rating, adjusted ampacity, termination ceiling, and overcurrent-protection limit answer different questions. For ordinary #10 copper applications, the separate 240.4(D) ceiling is 30 A. A 32 A adjusted ampacity does not authorize a 35 A breaker.
Likewise, selecting 90°C in the calculator must reflect an applicable equipment rating, not a way to remove an inconvenient limit. Special equipment and circuit exceptions need their own analysis outside this checker.
When the marking is unclear
Check the equipment instructions and the applicable default provisions in 110.14(C), or ask the manufacturer or qualified reviewer. A guessed rating can change the outcome even when the conduit fill is identical.