1. What is Motor Starting Current?

Starting current (or inrush current) is the instantaneous high current drawn by a 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 briefly until the motor reaches operating speed.

2. How Does the Calculator Work?

The calculator uses the simple formula:

Where:

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

Explanation: The inrush multiplier accounts for the brief period when the motor draws significantly more current than its rated full load current.

3. Importance of Starting Current Calculation

Details: Knowing the starting current is crucial for proper circuit breaker sizing, wire selection, and ensuring the electrical system can handle the temporary surge without nuisance tripping.

4. Using the Calculator

Tips: Enter the motor's full load amps (FLA) from its nameplate and the appropriate inrush multiplier (typically 6-8 unless manufacturer specifies otherwise).

5. Frequently Asked Questions (FAQ)

Q1: Why is starting current higher than running current?
A: The motor draws high current to overcome inertia and establish magnetic fields when starting. Once running, current drops to normal operating levels.

Q2: How long does starting current last?
A: Typically 0.1-30 seconds depending on motor size and load. Large motors may have longer start times.

Q3: Can starting current be reduced?
A: Yes, using soft starters, variable frequency drives (VFDs), or star-delta starters can reduce inrush current.

Q4: What happens if starting current is too high?
A: It can cause voltage dips, nuisance breaker trips, and excessive mechanical stress on the motor and driven equipment.

Q5: Is starting current the same as locked rotor current?
A: They're similar but not identical. Locked rotor current is measured with the rotor prevented from turning, while starting current occurs during normal acceleration.