Motor Full Load Current Calculator (kW ↔ HP)
Full load amps for three-phase and single-phase motors from power, voltage, power factor and efficiency — with kW ↔ HP conversion.
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Full Load Amps
Three-phase: I = P ÷ (√3 · U · cosφ · η); single-phase: I = P ÷ (U · cosφ · η) — where P is shaft (mechanical) power in watts, U line voltage, cosφ power factor (~0.85 typical) and η efficiency (~0.90). The tool also shows apparent power in kVA and converts kW ↔ HP (1 HP = 0.7457 kW). A 15 kW / 400 V motor draws about 28 A at full load — matching manufacturer tables.
Nameplate current on the actual motor wins over any formula: it reflects the real cosφ and η of that machine. Starting (inrush) current is 5-8× full load for direct-on-line starts — breakers and contactors are sized for that, not just FLA.
Frequently Asked Questions
Why does the calculated current differ from the nameplate?
Because cosφ and η vary per motor design and load. Adjust the two fields to the nameplate values and the numbers converge. When in doubt, the nameplate is authoritative.
What is kVA versus kW?
kW is real work at the shaft; kVA is what the supply must deliver, inflated by power factor and efficiency losses. Transformers and generators are sized in kVA for exactly this reason.
How do I size the breaker and contactor?
Not from full load amps alone — direct-on-line starting draws 5-8× FLA for a moment. Motor protection uses dedicated motor breakers or thermal relays set to FLA with a starting-tolerant curve. Follow the code and the motor manual.
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Motor Full Load Current Calculator (kW ↔ HP)