1. What is Motor Inrush Current?

Inrush current is the instantaneous high current drawn by a motor when it is first turned on. This current can be 6 to 8 times higher than the motor's full load current (FLA) and lasts only for a short duration (typically 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)
• \( Multiplier \) — Typically 6 to 8 depending on motor characteristics

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 crucial for proper sizing of circuit breakers, fuses, and other protective devices to prevent nuisance tripping while still providing adequate protection.

4. Using the Calculator

Tips: Enter the motor's full load current (FLA) in amps, select an appropriate multiplier (6 for conservative estimates, 8 for worst-case scenarios). All values must be valid (FLA > 0).

5. Frequently Asked Questions (FAQ)

Q1: Why does inrush current occur?
A: Inrush current occurs due to the need to magnetize the motor's core and overcome the initial inertia when starting.

Q2: How long does inrush current last?
A: Typically only a few AC cycles (fractions of a second), though it can last up to several seconds for very large motors.

Q3: What factors affect inrush current?
A: Motor design, load characteristics, applied voltage, and point in voltage waveform when starting.

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

Q5: Is inrush current the same as locked rotor current?
A: They are similar but not identical. Locked rotor current is sustained while the rotor is prevented from turning, while inrush current is the initial transient.