Motor Locked-Rotor Current from Code Letter (NEC 430.7(B))

NEC Table 430.7(B) maps the code letter (A-V) to a locked-rotor kVA/hp band, and locked_rotor_kva = hp x kVA/hp, LRA = kVA x 1000 / (sqrt(3) x V). A 25 hp code-G 460 V motor tops out at 6.29 kVA/hp -> 157 kVA -> 197 A (5.8x its 34 A FLA, so the rule of thumb fits); the same motor as code J (7.99 kVA/hp) draws 251 A -> 7.4x FLA, and an instantaneous-trip breaker or voltage-dip check sized on '6x' would be undersized. The code letter is about starting kVA and is NOT the design letter (A/B/C/D) for the torque-speed curve. A design aid; the nameplate and measured inrush govern.

kVA/hp = upper bound of the Table 430.7(B) code-letter band; locked_rotor_kva = hp x kVA/hp; LRA = kVA x 1000 / (sqrt(3) x V) three-phase, kVA x 1000 / V single-phase.

The NEC 2023 Table 430.7(B) locked-rotor indicating code letters, mapping the nameplate code letter to a locked-rotor kVA/hp band, by name; the motor nameplate and measured inrush govern.

NEC is free to read at nfpa.org/freeaccess. Table 430.7(B) and the locked-rotor kVA/hp bands are in the published code; the LRA relation is first-principles.

Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

Field names used by the API: horsepower, code_letter, voltage_v, phase, kva_per_hp, locked_rotor_kva, lra_a

• Band uses the upper end of each code-letter kVA/hp band for a conservative starting currentNEC Table 430.7(B)
• Not the design letter the code letter is about starting kVA; the design letter (A/B/C/D) describes the torque-speed curveNEC 430.7
• Rule of thumb '6x FLA' holds only for mid-range code letters; high-code motors draw 7-8xengineering practice