Max Motor HP for a Starting-Current Budget (NEC 430.7(B))
The inverse of the locked-rotor tile: the largest motor a starting-current budget (a breaker, a generator's starting kVA, an SCCR / voltage-dip ceiling) can start, max_hp = starting-current / (kVA/hp x 1000 / (sqrt(3) x V)). A 300 A budget on a code-G 460 V feeder tops out at ~38 hp. The code letter is the starting-kVA letter, not the design letter; a soft starter lowers the real inrush. A design aid; the nameplate governs.
Formula and source
max_hp = max_starting_current / (kVA/hp x 1000 / (sqrt(3) x V)) three-phase (kVA/hp x 1000 / V single-phase); the LRA = hp x kVA/hp x 1000 / (sqrt(3) x V) relation solved for the horsepower.
The NEC 2023 Table 430.7(B) locked-rotor indicating code letters, solved for the horsepower, by name; the motor nameplate and measured inrush govern.
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