1. What is Inrush Current?

Inrush current is the instantaneous high current drawn by an electrical device when first turned on. For motors, this can be 6-8 times the full load current (FLA) and lasts 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 most AC motors

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

3. Importance of Inrush Current Calculation

Details: Knowing inrush current is critical for proper circuit breaker and fuse sizing, preventing nuisance tripping, and ensuring electrical system stability during motor starting.

4. Using the Calculator

Tips: Enter the motor's full load current (FLA) in amps and the appropriate multiplier (typically 6-8). For exact values, consult motor specifications.

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, requiring much more current than during normal operation.

Q2: How long does inrush current last?
A: Typically 0.1-0.5 seconds for most motors, though large motors may have longer inrush durations.

Q3: Can inrush current damage equipment?
A: Repeated high inrush currents can stress electrical components. Soft starters or variable frequency drives can reduce inrush.

Q4: Do all motors have the same multiplier?
A: No, multipliers vary by motor type (e.g., 3-5 for high-efficiency motors, up to 12 for some specialty motors).

Q5: How does voltage affect inrush current?
A: Inrush current is directly proportional to applied voltage - lower voltage reduces inrush current.