Motor Starter Sizing

Motor Starter Sizing Calculator

How It Works & Sizing Logic

This calculator determines Full Load Current (FLC) and sizes motor starter panel components based on standard IEC 60947 recommendations, supporting both motor rating power input and direct nameplate current values.

Operating Modes & Calculation Formulas:

1. Calculate by Power (HP / kW): Calculates exact FLC considering adjustable Power Factor ($\cos\phi$) and Efficiency ($\eta$):
  • 3-Phase FLC: FLC = (kW × 1000) / (√3 × Voltage × cos φ × η)
  • 1-Phase FLC: FLC = (kW × 1000) / (Voltage × cos φ × η)
2. Direct Current Input (FLC from Nameplate): Uses the motor's actual full-load current directly from the nameplate to size panel components with maximum accuracy.
3. Component Sizing Factors (IEC 60947 Standard):
  • Main Circuit Breaker (MPCB/MCCB): Rated at 1.25 × FLC – 1.50 × FLC to accommodate motor starting inrush current.
  • AC-3 Line Contactor: Minimum rating = 1.15 × FLC for continuous motor load duty.
  • Thermal Overload Relay: Adjustable setting range set between 0.80 × FLC and 1.20 × FLC (Center set point = 1.0 × FLC).
*Power conversion: 1 HP = 0.746 kW