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Motor Branch Circuit Sizing (NEC 430) | Engineering Database

Motor Branch Circuit Sizing (NEC 430)

electrical

Sizes motor branch circuit components per NEC Article 430: conductor ampacity (430.22), overcurrent protection (430.52), overload relay settings (430.32), and feeder sizing for multiple motors (430.24/430.62).

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Hp*

Motor nameplate horsepower. Must match an NEC Table 430.248/250 entry (common: 0.5–500 HP).

Voltage

Motor nameplate voltage in volts. Standard values: 115, 200, 208, 230, 460, 480, 575 V. Standard: 208V small motors, 480V commercial/industrial, 4160V large motors. If omitted, defaults to 480 V.

Phases

Number of electrical phases. Use 1 for single-phase or 3 for three-phase motors. If omitted, defaults to 3.

Motor Type

Motor type key matching the motor-flc table. Common values: 'ac_induction_3phase', 'ac_induction_1phase', 'dc'. If omitted, defaults to 'ac_induction_3phase'.

Ocpd Type

Overcurrent protective device type per NEC 430.52. Determines the maximum OCPD multiplier applied to FLC. If omitted, defaults to 'inverse_time_breaker'.

Num Motors On Feeder

Number of identical motors on the feeder. When >1, feeder sizing per NEC 430.24/430.62 is calculated. Typical: 1-6 motors per feeder. If omitted, defaults to 1 (single motor, no feeder sizing).

Service Factor

Motor service factor from nameplate. SF >= 1.15 allows 115% overload relay setting; otherwise 125% per NEC 430.32. Standard: 1.15 for NEMA Design B. Check nameplate — affects overload setting. If omitted, defaults to 1.15.

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Reference data

This calculator pulls live values from the following engineering reference tables in the database.

motor flc
nec ocpd ratings
motor efficiency

About this calculator

Motor Branch Circuit Sizing (NEC 430) is part of the Engineering Database calculator suite. Each tool runs deterministic calculations against authoritative reference data and code-compliant methods, so results are reproducible and traceable to source standards.

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