1. What is Motor Starting Current?

Motor starting current (or inrush current) is the instantaneous current drawn by a motor when it is first turned on. This current is typically much higher than the normal running current (FLA) and lasts only briefly as the motor comes up to speed.

2. How Does the Calculator Work?

The calculator uses the motor starting current formula:

Where:

• \( FLA \) — Full Load Amps (normal operating current)
• \( Inrush\ Multiplier \) — Typically 6-8 times FLA for most AC induction motors

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

3. Importance of Starting Current Calculation

Details: Knowing the starting current is crucial for proper circuit breaker and fuse selection, voltage drop calculations, and ensuring the power supply can handle the initial surge without nuisance tripping.

4. Using the Calculator

Tips: Enter the motor's full load current (FLA) in amps and the appropriate inrush multiplier (typically 6-8). For exact values, consult the motor manufacturer's specifications.

5. Frequently Asked Questions (FAQ)

Q1: Why is starting current higher than running current?
A: At startup, the motor has no back-EMF and draws more current to establish magnetic fields and overcome inertia.

Q2: How long does the starting current last?
A: Typically 0.1-30 seconds depending on motor size and load, until the motor reaches about 75% of full speed.

Q3: What affects the inrush multiplier?
A: Motor design, load characteristics, and starting method (DOL, star-delta, soft starter, etc.).

Q4: Can starting current damage the motor?
A: Normally no, as it's brief. But frequent starts can cause overheating due to I²R losses.

Q5: How to reduce starting current?
A: Use soft starters, variable frequency drives, or star-delta starters to limit inrush current.