1. What is Motor Rated Current?

The motor rated current is the current a motor draws from the power supply when operating at its rated power, voltage, and frequency under full load conditions. It's a crucial parameter for selecting proper protection devices and conductors.

2. How Does the Calculator Work?

The calculator uses the 3-phase motor current formula:

Where:

• \( I \) — Rated current (amps)
• \( P \) — Motor power (watts)
• \( V \) — Line voltage (volts)
• \( PF \) — Power factor (0-1)
• \( \eta \) — Motor efficiency (0-1)

Explanation: The formula accounts for the three-phase power system (√3 factor) and the motor's power factor and efficiency which affect the actual current draw.

3. Importance of Current Calculation

Details: Knowing the rated current is essential for proper circuit design, selecting appropriate wire sizes, circuit breakers, overload protection, and contactors to ensure safe and reliable motor operation.

4. Using the Calculator

Tips: Enter motor power in watts, line voltage in volts, power factor (typically 0.8-0.95 for motors), and efficiency (typically 0.8-0.95). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What's typical power factor for motors?
A: Induction motors typically have 0.8-0.9 PF at full load, dropping to 0.2-0.3 at no load. Synchronous motors can achieve 1.0 PF.

Q2: How does voltage affect current?
A: Current is inversely proportional to voltage. A 10% voltage drop increases current by about 11% to deliver same power.

Q3: What's motor efficiency range?
A: Small motors (50-75%), medium (80-90%), large premium efficiency motors (93-97%).

Q4: How to account for starting current?
A: Starting current (inrush) is typically 5-8 times rated current but lasts only seconds. Special protection devices are needed.

Q5: Single-phase motor formula?
A: For single-phase: \( I = P / (V \times PF \times \eta) \) (no √3 factor).