Motor Contactor Size Calculator

Determine the correct contactor size for your motor applications

Motor Contactor Size Calculator

Compliant with IEC 60034 Standards

Results:

Motor FLC (A): 0.00

Contactor Size (A): 0.00

Making/Breaking Capacity (A): 0.00

Motor Capacitor Calculator
Motor Breaker Size Calculator

How to Use the Calculator

AC Single Phase Motor

  1. Select "kW" or "HP" for Motor Power and enter value.
  2. Enter the motor's rated Voltage (V).
  3. Choose "Single Phase" for Phase.
  4. Input the motor's Power Factor (PF) (0-1).
  5. Enter the Service Factor (SF) (e.g., 1.15, 1.25).

AC Three Phase Motor

  1. Select "kW" or "HP" for Motor Power and enter value.
  2. Enter the motor's rated Line-to-Line Voltage (V).
  3. Choose "Three Phase" for Phase.
  4. Input the motor's Power Factor (PF) (0-1).
  5. Enter the Service Factor (SF) (e.g., 1.15, 1.25).

Motor Contactor Sizing Fundamentals

Full Load Current (FLC)

FLC is the current drawn by a motor when operating at its rated power and voltage. It's crucial for sizing protective devices and control components like contactors.

  • Depends on motor power, voltage, and efficiency.
  • Higher FLC requires larger contactor ratings.

Service Factor (SF)

  • A multiplier applied to the FLC to account for continuous operation, overloads, and safety margins.
  • Common SF values are 1.15 or 1.25.
  • Ensures the contactor can handle peak loads without premature failure.

Key Formulas:

kW = HP × 0.746

Single Phase AC FLC: I = (P × 1000) / (V × PF)

Three Phase AC FLC: I = (P × 1000) / (√3 × V × PF)

Contactor Size = FLC × SF

Making/Breaking Capacity = 8 × FLC

Calculation Formulas

Motor Power Conversion:
P(kW) = P(HP) × 0.746

AC Single Phase FLC:
FLC = (P_kW × 1000) / (V × PF)

AC Three Phase FLC:
FLC = (P_kW × 1000) / (√3 × V × PF)

Recommended Contactor Size:
Contactor Size = FLC × SF

Making/Breaking Capacity:
Making/Breaking Capacity = 8 × FLC

Example Calculation

Three Phase AC Motor:

Motor Power: 10 kW

Voltage: 400V

PF: 0.85

SF: 1.25

FLC = (10 × 1000) / (√3 × 400 × 0.85) ≈ 16.98 A

Contactor Size = 16.98 A × 1.25 ≈ 21.23 A

Making/Breaking Capacity = 16.98 A × 8 ≈ 135.84 A

Motor FLC = 16.98 A | Contactor Size = 21.23 A | Making/Breaking Capacity = 135.84 A

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