1. What is Motor Inrush Current?

Inrush current is the instantaneous high current drawn by an electric motor when it is first turned on. This current can be 6-8 times higher than the motor's full load current (FLA) and lasts only for a short duration until the motor reaches its operating speed.

2. How Does the Calculator Work?

The calculator uses the inrush current formula:

Where:

• \( \text{FLA} \) — Full Load Amps (the motor's rated current at full load)
• \( \text{Inrush Multiplier} \) — Typically 6-8 for most AC induction motors

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

3. Importance of Inrush Current Calculation

Details: Knowing the inrush current is critical for proper circuit breaker and fuse sizing, preventing nuisance tripping, and ensuring electrical system reliability.

4. Using the Calculator

Tips: Enter the motor's full load current (FLA) in amps and the appropriate inrush multiplier (typically 6-8). The FLA can usually be found on the motor nameplate.

5. Frequently Asked Questions (FAQ)

Q1: Why is inrush current higher than running current?
A: At startup, the motor has no back-EMF and appears as a short circuit to the power supply, drawing high current until it begins rotating.

Q2: How long does inrush current last?
A: Typically 0.1-0.5 seconds for small motors, up to several seconds for large motors.

Q3: Can inrush current damage equipment?
A: Repeated high inrush currents can stress electrical components and reduce their lifespan if not properly protected.

Q4: How can inrush current be reduced?
A: Using soft starters, variable frequency drives (VFDs), or star-delta starters can significantly reduce inrush current.

Q5: Does inrush current affect power factor?
A: Yes, during startup the power factor is very low (highly reactive) before improving as the motor reaches operating speed.