1. What is Inrush Current?

Inrush current is the instantaneous high current drawn by an electrical device when first turned on. For motors, this current can be 6-8 times higher than the normal full load current, lasting for a few cycles until the motor reaches operating speed.

2. How Does the Calculator Work?

The calculator uses the inrush current formula:

Where:

• FLA — Full Load Amps (normal operating current)
• Inrush Multiplier — Typically 6-8 for induction motors

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 crucial for proper circuit breaker sizing, wire selection, and preventing nuisance tripping. It also helps in designing soft-start systems.

4. Using the Calculator

Tips: Enter the motor's full load current (FLA) in amps (found on nameplate) and the appropriate multiplier (typically 6-8 for standard induction motors).

5. Frequently Asked Questions (FAQ)

Q1: Why is inrush current higher than running current?
A: At startup, the motor needs to overcome inertia and establish magnetic fields before back-EMF develops to limit current.

Q2: How long does inrush current last?
A: Typically 3-10 cycles (50-200ms) for standard motors, though large motors may have longer inrush durations.

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

Q4: What affects the inrush multiplier value?
A: Motor design, load inertia, and starting method. 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 measured with the rotor prevented from turning.