Motor circuit conductor sizing follows NEC Article 430 rather than the general wire sizing rules in Article 310. Motor branch circuit conductors must be sized at a minimum of 125% of the motor full load current (FLC) from NEC Tables 430.248–430.250, not the motor nameplate current. The motor full load current tables account for normal motor characteristics and provide the basis for all motor circuit sizing. From the FLC: conductors are sized at 125% FLC, overload protection is set at 115–125% of nameplate current, and the branch circuit OCPD can be up to 250% of FLC for inverse-time breakers. This calculator performs the full NEC Article 430 motor circuit sizing automatically.
10 HP, 460V, 3-phase motor: NEC Table 430.250 FLC = 14A. Branch circuit conductor minimum = 14 × 1.25 = 17.5A → 12 AWG copper (20A at 75°C). OCPD (inverse-time breaker) max = 14 × 2.5 = 35A → use 35A breaker.
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