Motor Current Calculator

Motor Current Calculator for Formula Amps, Nameplate Checks, and NEC Next Steps

Use this page when you need to estimate or compare motor current from the motor's operating data: horsepower or kW, voltage, efficiency, and power factor. For example, a 10 HP, 460V, three-phase motor at 90% efficiency and 0.85 power factor calculates to about 12.2 A by formula, while the NEC 430.250 table value for the same HP and voltage is 14 A. That comparison is useful because formula current, NEC table FLC, nameplate FLA, starting current, and protection settings do not all serve the same job.

What Each Mode Does

• NEC Table FLC vs Formula Current - compares entered motor data with the NEC table full-load current for the selected horsepower, voltage, and phase count.
• Starting Current Screen - provides only a light bridge to inrush planning. Use the dedicated Motor Starting Current Calculator when the task is really locked-rotor current, inrush, DOL, star-delta, soft starter, VFD, or autotransformer comparison.
• Operating Current - estimates running current, kW, kVAR, and kVA from the entered power, efficiency, and power factor.
• Preliminary Branch-Circuit Sizing - shows why branch work starts from NEC table FLC, then points deeper conductor and protection tasks toward the dedicated FLC, cable-sizing, and protection calculators.

FLC vs FLA: The NEC Distinction That Drives the Whole Page

NEC 430.6(A)(1) sends branch-circuit conductor sizing and branch-circuit short-circuit and ground-fault protection back to the standard ampere ratings in the NEC motor tables. For the AC motors covered by this page, that means Table 430.248 for single-phase motors and Table 430.250 for three-phase motors.

NEC 430.22 then uses that table full-load current for conductor ampacity. NEC 430.32 is different: overload devices are based on actual motor nameplate current, not the NEC table value. That is why this calculator does not pretend that one current value does every job.

Three-Phase NEC Table 430.250 Quick Reference

The following values are common checkpoints for three-phase AC motors. They are useful when you want to sanity-check the calculator output or compare nearby horsepower values before moving to conductor and breaker review.

How the Branch-Circuit Sizing Screen Is Framed

The branch-circuit sizing mode is intentionally narrow. It uses 125% of NEC table FLC for a conductor ampacity screen under NEC 430.22 and applies a 250% inverse-time circuit-breaker screen under NEC 430.52 and NEC 240.6(A) standard sizes. For overload devices, the page only calculates a setting if you enter actual nameplate FLA, because that is what NEC 430.32 uses.

Starting Current Mode Is a Screening Tool, Not a Locked-Rotor Study

The starting-current mode uses common planning multipliers for DOL, star-delta, soft starter, VFD, and autotransformer starts. That is helpful for quick feeder and nuisance-trip discussions, but it is not a replacement for locked-rotor current data, commissioned soft-starter current limits, VFD overload settings, or a manufacturer starting study. For deeper inrush work, use the dedicated Motor Starting Current Calculator.

When to Use the Dedicated Full Load Current Tool Instead

If your job is only to look up NEC table current and branch-circuit sizing from horsepower, voltage, and phase count, use the Full Load Current Calculator. That page is the direct lookup page for examples such as NEC Table 430.250 10 HP 460V FLC and 200 HP 460V FLC. When the next question is motor branch short-circuit and ground-fault protection, move from the FLC result to the Motor Branch Protection Calculator, not to the general breaker page first. This page keeps formula current, operating-current review, and the next-step links together for one-motor planning.

Worksheet Follow-Ups After the Current Result

Use this current page for formula amps, table FLC comparison, and nameplate FLA context. Use the Motor Nameplate Data Worksheet when the next step is recording nameplate FLA, service factor, duty, and manufacturer notes. Use the Motor Contactor Selection Worksheet when coil voltage, NEMA basis, auxiliary contacts, enclosure, and SCCR notes need to stay with the starter selection.

What the Page Does Not Claim

This calculator does not claim to size every motor circuit in every condition. It does not handle every specialty motor type, every reduced-voltage starter detail, every conductor derating case, or every branch-circuit protection device option. Use it as an honest AC motor planning page, then verify the final design with the adopted NEC edition, actual nameplate data, and manufacturer documentation.