Two answers in one verdict: the standard breaker rating (125% of continuous load, NEC 210.20(A)) and the minimum conductor that legally pairs with it — because a breaker protects the wire, and the pair must be sized together.
Size in this order: load → breaker → wire. A continuous load is multiplied by 125%, rounded up to a standard rating; the conductor's ampacity must then meet or exceed that rating, with the NEC 240.4(D) small-conductor caps applied (14 AWG copper is capped at 15 A, 12 at 20 A, 10 at 30 A, regardless of what the 75 °C table says). The wire shown here is the thermal minimum — on any run past ~75 ft, voltage drop usually demands a bigger conductor, which is fine: the breaker protects the smaller of the pair, and bigger wire on a given breaker is always legal.
Oversizing a breaker to stop nuisance trips is the classic dangerous mistake — it removes the wire's protection. If a breaker trips on a correctly sized circuit, the problem is the load or the circuit design, not the breaker.
| 125% | NEC 210.20(A): continuous loads (3+ hours) need 25% headroom |
| standard | ratings climb 15, 20, 25, 30, 35, 40, 45, 50, 60 A… |
| 240.4(D) | small-conductor caps: 14 Cu→15 A, 12 Cu→20 A, 10 Cu→30 A |
The breaker protects the wire — size load → breaker → wire, in that order, and never upsize a breaker to stop trips.
32 × 1.25 = 40 A — and 8 AWG copper minimum to pair with it. The calculator applies exactly this chain.
Always — upsizing wire for voltage drop while keeping the breaker matched to the load is standard practice. The reverse (breaker bigger than the wire's rating) is the violation.