All-in-One Motor Calculator | HP, Current, Cable Size & Protection

All-in-One Motor Calculator

Professional Electrical Engineering Tool | IEEE/IEC Standards

CircuitSecrets.com

Common Input Parameters

Motor Phase

Line Voltage V

Required

Line Current A

Motor Power HP/kW

Power Factor (cos φ) pu

0-1

Efficiency %

0-100

Frequency Hz

Motor Speed RPM

Cable Length m

Conductor Material Copper Aluminium

Installation Method Method A (Bunched) Method B (Tray) Method C (Conduit) Method D (Direct)

Ambient Temperature °C

Starting Method DOL (Direct-On-Line) Star-Delta Soft Starter

Formulas: Single Phase: P = V × I × PF × η | Three Phase: P = √3 × V × I × PF × η

Motor Power Calculations

Formula: P_out = V × I × PF × η (1Φ) | P_out = √3 × V × I × PF × η (3Φ)
HP Conversion: HP = kW / 0.746

Full Load Current (FLC)

IEC Standards: FLC calculation based on motor power, voltage, efficiency and power factor.
Formula: I_FLC = P_out / (√3 × V × PF × η) [3Φ] | I_FLC = P_out / (V × PF × η) [1Φ]

Cable Size Selection

Standards: IEC 60364 / BS 7671 | Derating Factors: Temperature, Installation Method
Rule: Selected cable must carry FLC with derating applied

Voltage Drop Calculation

Limit: 5% maximum (IEC/IEEE)
Formula: V_drop = (2 × L × I × R × cos φ) / 1000 [1Φ] | V_drop = (√3 × L × I × R × cos φ) / 1000 [3Φ]

Protection Devices

Standards: IEC 60947 / BS 88 | MCB: 1.25 × FLC | MCCB: 1.25 × FLC
Contactor: 1.5 × FLC | Overload: 1.15 × FLC | Fuse: 1.5 × FLC

Starting Current

DOL: 5-7 × FLC | Star-Delta: 2.5-3.5 × FLC (starting) / 1.73 × FLC (running)
Soft Starter: 2.5-4 × FLC | VFD: 1.2-1.5 × FLC

Torque & Slip

Torque: T = 9550 × kW / RPM (IEC Standard)
Slip: S = (N_s - N_r) / N_s × 100%
Synchronous Speed: N_s = 120 × f / P

⚠️ Disclaimer:

This calculator is for estimation purposes only. Always verify with motor nameplate data and consult local electrical codes (NEC, IEC, BS 7671) before installation. Professional engineering judgment required.

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