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Three-Phase Motor Full-Load Current

Also known as FLA · motor amps · full load amps

I=Pout3 V PF ηI = \frac{P_{out}}{\sqrt{3} \, V \, \text{PF} \, \eta}
sig figs

Worked example: 10 hp, 460 V, 0.85 PF, 89% → 12.37 A. Press Try an example to run it live, then adjust anything.

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Constant used: built into this formula, no need to enter
3=1.7320508075688772\sqrt{3} = 1.7320508075688772Square Root of Three · exact

Where Three-Phase Motor Full-Load Current fits

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Available Short-Circuit Current from Percent ImpedanceThree-Phase Apparent Power
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See also

Motor Efficiency: Both use shaft output power and motor efficiency.Three-Phase Apparent Power: Both use full-load line current and line-to-line voltage.Three-Phase Real Power: Both use line-to-line voltage and power factor.Transformer Full-Load Current: Both use full-load line current.Available Short-Circuit Current from Percent Impedance: Both use full-load line current.Motor Locked-Rotor Starting Current: Both use line-to-line voltage.
7 more relatedWye Line and Phase Voltage: Both use line-to-line voltage.Phase Angle from Power Factor: Both use power factor.Power Factor from Real and Apparent Power: Both use power factor.Power-Factor Correction kvar: Both use power factor.Single-Phase Real Power with Power Factor: Both use power factor.Transformer Efficiency from Core and Copper Losses: Both use power factor.Motor Torque from Power and Speed: Both use shaft output power.
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Three-Phase Motor Full-Load Current explained

MηVIPoutPF

A motor's rating is what comes out of the shaft; the line must supply that plus the losses, and it must supply it through a phase angle. So the input volt-amperes are Pout/(η · PF), and dividing by √3 V gives the line current. A 10 hp, 460 V motor at 89% efficiency and 0.85 PF draws 7457/(1.732 × 460 × 0.85 × 0.89) ≈ 12.4 A: reassuringly close to the 14 A that NEC Table 430.250 lists for sizing.

Use the code table, not this calculation, for conductor and overload sizing in North America: the NEC deliberately tabulates conservative currents and requires them for branch-circuit design, reserving nameplate amps for overload protection. Use this formula instead when you want to know what a specific machine really draws, to sanity-check a clamp-meter reading, or to see how an unloaded motor's collapsing power factor pushes current up out of proportion to the work being done.

Three-Phase Motor Full-Load Current formula

I=Pout3 V PF ηI = \frac{P_{out}}{\sqrt{3} \, V \, \text{PF} \, \eta}
Where
  • II= Full-load line current (A)
  • PoutP_{out}= Shaft output power (W)
  • VV= Line-to-line voltage (V)
  • PF\text{PF}= Power factor
  • η\eta= Efficiency (%)
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Motor calculations

5 formulasFull-load current, synchronous speed, slip, efficiency and input power — reading a motor nameplate and checking what it actually draws.

Revised 30 October 2026
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formula.expert. (2026, October 30). Three-Phase Motor Full-Load Current Formula & Calculator. https://formula.expert/solvers/motor-full-load-current-three-phase

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