Three-Phase Motor Sizing Calculator
kW + V + cos φ + efficiency → current + protection
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Three-Phase Motor Sizing Calculator
Full-load current, locked-rotor amps, recommended overload protection. From kW + voltage + power factor + efficiency. IEC standard sizing.
How to use this tool
- 1
Motor rating
kW + voltage + cos φ + efficiency.
- 2
See full-load current
Plus locked-rotor amps.
- 3
Protection sizing
Overload + short-circuit recommendations.
Frequently Asked Questions
Three-phase current formula?
I = P / (√3 × V × cos φ × η). Power in W, voltage line-to-line, cos φ = power factor, η = efficiency. For 11 kW @ 400V, 0.85 PF, 92% eff: I = 11000 / (1.732 × 400 × 0.85 × 0.92) ≈ 20.3 A.
Locked-rotor (starting) current?
Typically 5-7× full-load current. Code letter on nameplate: B = 6.3-7.1 kVA/HP, F = 5.0-5.6, etc. Affects upstream protection + cable sizing.
Overload protection setting?
Per IEC: 1.05-1.20 × full-load current (FLA). For class 10A relay (most common): 1.15 × FLA. Set higher for high-inertia loads (compressor, fan with damper).
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