Calculators
Motor Feeder Sizing (NEC 430)
Single-motor branch-circuit conductor, overload, short-circuit/ground-fault (SCGF) protection, and disconnect sizing per NEC 2023 Article 430. FLC values from NEC Table 430.250 (three-phase AC); SCGF multipliers from Table 430.52; ambient and conduit-fill derating from 310.15.
Method: Branch-circuit conductor min ampacity (430.22) = 125% · FLC (Table 430.250). Overload (430.32): if SF ≥ 1.15 or rise < 40°C use 125% · nameplate FLA, else 115%. SCGF max device size (430.52): inverse-time CB 250%, time-delay fuse 175%, non-time fuse 300%, instant-trip CB 800% of FLC. Disconnect (430.110) = 115% · FLC. Ambient correction per 310.15(B)(1) for 75°C-rated insulation: 1.00 ≤86°F, 0.94 ≤95°F, 0.88 ≤104°F, 0.82 ≤113°F, 0.75 >113°F. Conduit-fill adjustment per 310.15(C)(1): 100% for ≤3 CCCs, 80% for 4–6, 70% for 7–9, 50% for 10–20, 45% for >20. Corrected ampacity required = (125% · FLC) / (ambient · fill). Does not cover VFD-fed motors (see 430.130 Part X) or DC motors (Table 430.247). References: NEC 2023 Article 430; Tables 430.250, 430.52, 310.16; 310.15(B)(1) and 310.15(C)(1); IEEE 242 (Buff Book).
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