1. What is Inrush Current?

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

2. How Does the Calculator Work?

The calculator uses the inrush current formula:

Where:

• \( \text{FLA} \) — Full Load Amps (normal operating current)
• \( \text{Inrush Multiplier} \) — Typically 6-8 for most motors

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

3. Importance of Inrush Current Calculation

Details: Calculating inrush current is crucial for proper circuit breaker sizing, wire selection, and preventing nuisance tripping of protective devices.

4. Using the Calculator

Tips: Enter the motor's full load current (FLA) in amps and the appropriate multiplier (typically 6-8). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: Why is inrush current higher than running current?
A: Motors initially draw high current to overcome inertia, magnetize cores, and charge capacitors before settling to normal operating current.

Q2: How long does inrush current last?
A: Typically 3-30 electrical cycles (50-500ms at 60Hz), depending on motor size and design.

Q3: Can inrush current damage equipment?
A: Repeated high inrush can stress contacts and reduce equipment life. Proper sizing of components is essential.

Q4: How to reduce inrush current?
A: Soft starters, variable frequency drives (VFDs), or star-delta starters can limit inrush current.

Q5: Do all motors have the same multiplier?
A: No, high-efficiency motors may have higher multipliers (8-12x), while some designs like NEMA Design B are typically 6-8x.