1. What is 3 Phase Motor Inrush Current?

The inrush current is the instantaneous high current drawn by a motor when it is first turned on. This current can be several times higher than the motor's normal operating current and is important for sizing circuit protection devices.

2. How Does the Calculator Work?

The calculator uses the inrush current formula:

Where:

• \( Code\ Factor \) — Motor code letter factor (kVA/hp)
• \( HP \) — Motor horsepower
• \( V \) — Line voltage (volts)

Explanation: The equation calculates the approximate inrush current based on the motor's code letter, horsepower rating, and operating voltage.

3. Importance of Inrush Current Calculation

Details: Knowing the inrush current is critical for proper selection of circuit breakers, fuses, and other protective devices to prevent nuisance tripping while still providing adequate protection.

4. Using the Calculator

Tips: Enter the code factor from the motor nameplate (in kVA/hp), the motor's horsepower rating, and the operating voltage. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical code factor range?
A: Code factors typically range from 3.14 (Code A) to 22.4 (Code K) kVA/hp, with most motors falling between 5-10 kVA/hp.

Q2: How long does inrush current last?
A: Typically 0.1-0.5 seconds, though it can last longer for large motors or under heavy load conditions.

Q3: Why is the square root of 3 in the formula?
A: For three-phase systems, the square root of 3 (≈1.732) accounts for the phase relationships between the three voltage waveforms.

Q4: Can this be used for single-phase motors?
A: No, this formula is specifically for three-phase motors. Single-phase motors have different inrush characteristics.

Q5: How accurate is this calculation?
A: It provides a good estimate but actual inrush may vary based on specific motor design, load conditions, and power system characteristics.