1. What is Motor Inrush Current?

Inrush current is the instantaneous high current drawn by an electric motor when it is first turned on. This current can be 5 to 7 times higher than the motor's full load current (FLA) and lasts only for a few cycles.

2. How Does the Calculator Work?

The calculator uses the inrush current formula:

Where:

• \( I_{inrush} \) — Inrush current in amps
• \( FLA \) — Full load amps (motor's rated current)
• \( 5 \text{ to } 7 \) — Multiplier based on motor characteristics

Explanation: The multiplier accounts for the initial surge of current needed to overcome the motor's inertia and establish magnetic fields.

3. Importance of Inrush Current Calculation

Details: Knowing inrush current is critical for proper sizing of circuit breakers, fuses, and other protective devices to prevent nuisance tripping while still providing adequate protection.

4. Using the Calculator

Tips: Enter the motor's full load current (FLA) from its nameplate. Select a multiplier (5 for conservative estimates, 7 for worst-case scenarios). All values must be valid (FLA > 0).

5. Frequently Asked Questions (FAQ)

Q1: Why does inrush current occur?
A: Inrush current occurs because the motor draws high current to establish magnetic fields and overcome initial inertia when starting.

Q2: How long does inrush current last?
A: Typically 5-30 cycles (0.1-0.5 seconds for 60Hz systems), depending on motor size and design.

Q3: Can inrush current be reduced?
A: Yes, through soft starters, variable frequency drives, or star-delta starting configurations.

Q4: What affects the multiplier value?
A: Motor design, efficiency, and load characteristics. High-efficiency motors often have higher inrush currents.

Q5: Is inrush current the same as locked rotor current?
A: They're similar but not identical. Locked rotor current is sustained when the motor can't turn, while inrush current is transient during normal startup.