1. What is the Locked Rotor Amps Calculation?

The Locked Rotor Amps (ILR) calculation determines the current drawn by an electric motor when its rotor is locked and full voltage is applied. This is an important parameter for motor protection and circuit design.

2. How Does the Calculator Work?

The calculator uses the ILR formula:

Where:

• \( FLA \) — Full Load Amps (amps)
• \( \frac{LRA}{FLA} \) — Locked Rotor Amps to Full Load Amps ratio (unitless)

Explanation: The equation calculates the maximum current a motor will draw during startup when the rotor is stationary.

3. Importance of ILR Calculation

Details: Accurate ILR calculation is crucial for proper sizing of motor starters, circuit breakers, fuses, and other protective devices to prevent nuisance tripping while ensuring adequate motor protection.

4. Using the Calculator

Tips: Enter FLA in amps and the LRA/FLA ratio (typically between 5-8 for most motors). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical LRA/FLA ratio for AC motors?
A: For most AC induction motors, the LRA/FLA ratio typically ranges from 5 to 8, but can be higher for some specialized motors.

Q2: Why is locked rotor current important?
A: It helps determine the required interrupting capacity of protective devices and ensures proper motor starting without causing voltage dips that could affect other equipment.

Q3: How is LRA/FLA ratio determined?
A: The ratio is typically provided by the motor manufacturer and can be found on the motor nameplate or in technical specifications.

Q4: Does motor size affect the LRA/FLA ratio?
A: While the ratio is relatively consistent across motor sizes, larger motors may have slightly lower ratios due to design differences.

Q5: Can this calculation be used for DC motors?
A: No, this calculation is specific to AC induction motors. DC motors have different starting characteristics.