A motor's FLC is 40 A. Using an inverse-time circuit breaker at the maximum percentage generally permitted by Table 430.52(C)(1) for branch-circuit short-circuit and ground-fault protection (250%), what is the maximum standard breaker rating?
Not quite. The answer is C: 100 A
40 A × 250% = 100 A, which is itself a standard breaker size, so no rounding is needed here. This maximum percentage exists so the breaker can ride through a motor's brief high-inrush starting current without nuisance tripping, while still clearing an actual short circuit or ground fault — it is not sized to protect the motor from ordinary overload, which is the overload relay's job.
Reference: NEC 2023 Table 430.52(C)(1) (Maximum Rating — Inverse-Time Breaker)
Checked against multiple published sources
A Mike Holt motor chart (inverse-time breaker at 250% of FLC per Table 430.52(C)(1) and 240.6(A)) and an ECM article (examples at 250%, citing 430.52(C)(1) Ex 1; based on the 2011 NEC) agree. An ECM 2023 NEC article (read 2026-11-03) confirms the 2023 NEC names the table Table 430.52(C)(1) (formerly Table 430.52) with requirements unchanged from 2020. Neither is the code text.