1. What is Inrush Current?

Inrush current is the instantaneous high current drawn by an electrical device when first turned on. For three-phase motors, this current is typically 6-8 times the full load current and lasts only for a few cycles.

2. How Does the Calculator Work?

The calculator uses the inrush current formula:

Where:

• \( Inrush \) — Inrush current in amps
• \( I \) — Full load current in amps

Explanation: The formula provides a conservative estimate of inrush current, using the lower end of the typical 6-8 times multiplier for three-phase motors.

3. Importance of Inrush Current Calculation

Details: Calculating inrush current is crucial for proper circuit protection, preventing nuisance tripping of breakers, sizing transformers, and selecting appropriate motor starters and contactors.

4. Using the Calculator

Tips: Enter the full load current in amps. The value must be greater than zero. The calculator will estimate the approximate inrush current.

5. Frequently Asked Questions (FAQ)

Q1: Why is inrush current higher than running current?
A: Inrush current is high because the motor's rotor is stationary at startup, requiring more current to overcome inertia and establish the magnetic field.

Q2: How long does inrush current last?
A: Typically only a few cycles (less than a second), but the duration depends on motor size, design, and load characteristics.

Q3: When is the 8x multiplier used instead of 6x?
A: The higher multiplier is used for more conservative estimates or for motors with higher starting torque requirements.

Q4: How can inrush current be reduced?
A: Using soft starters, variable frequency drives, or reduced voltage starting methods can limit inrush current.

Q5: Does inrush current affect power quality?
A: Yes, high inrush currents can cause voltage sags that may affect other equipment on the same electrical system.