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 5 to 30 times higher than the motor's normal running current and typically lasts for a few cycles of the input waveform.

2. How Does the Calculator Work?

The calculator uses the standard inrush current estimation formula:

Where:

• \( I_{inrush} \) — Inrush current (Amps)
• \( I_{steady} \) — Steady-state operating current (Amps)
• 30 — Typical multiplier for AC induction motors

Explanation: The multiplier of 30 is a conservative estimate that accounts for the worst-case scenario when a motor is started at the peak of the voltage waveform.

3. Importance of Inrush Current Calculation

Details: Knowing the inrush current is critical for proper sizing of circuit breakers, fuses, and other protective devices. It also helps in voltage drop calculations and determining if soft-start systems are needed.

4. Using the Calculator

Tips: Enter the motor's steady-state operating current in amps. The value must be greater than zero. The calculator will estimate the worst-case inrush current.

5. Frequently Asked Questions (FAQ)

Q1: Is the multiplier always 30?
A: No, the actual multiplier varies (typically 5-30) depending on motor design. 30 is a conservative estimate for worst-case scenarios.

Q2: How long does inrush current last?
A: Typically 3-10 cycles of the AC waveform (50-200 milliseconds at 50/60Hz), though this varies by motor size and design.

Q3: Can inrush current be reduced?
A: Yes, through soft-start systems, variable frequency drives, or star-delta starters.

Q4: Why is inrush current higher than running current?
A: At startup, the motor's rotor is stationary, presenting very low impedance to the power supply, resulting in high current flow.

Q5: Does inrush current affect power quality?
A: Yes, large motors starting can cause voltage sags that may affect other equipment on the same circuit.