1. What is Inrush Current?

Inrush current is the instantaneous high current drawn by an electrical device when first turned on. For 3-phase motors, this current can be 6-8 times higher than the normal full load current (FLA) and lasts for a few cycles.

2. How Does the Calculator Work?

The calculator uses the inrush current formula:

Where:

• \( FLA \) — Full Load Amps (motor's rated current at full load)
• \( Inrush\ Multiplier \) — Typically 6-8 for most 3-phase 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 critical for proper circuit breaker sizing, overload protection selection, and preventing nuisance tripping during motor startup.

4. Using the Calculator

Tips: Enter the motor's full load current (FLA) from its nameplate and the appropriate multiplier (6-8 is typical, but consult manufacturer specs for exact values).

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 3-30 electrical cycles (50-500ms at 60Hz), depending on motor size and load.

Q3: What affects the inrush multiplier?
A: Motor design, winding type, load inertia, and starting method (DOL, star-delta, soft start).

Q4: Can inrush current damage equipment?
A: Repeated high inrush can stress contacts and windings. Proper protection devices are essential.

Q5: How to reduce inrush current?
A: Use soft starters, variable frequency drives, or star-delta starting methods.