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3-Phase Motor Amperage Calculator

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1. What is a 3-Phase Motor Amperage Calculator?

Definition: This calculator computes the current (I) drawn by a 3-phase motor at full load, based on its power rating, voltage, power factor, and efficiency.

Purpose: It is used in electrical engineering to determine the current requirements for motor circuits, aiding in the design of wiring, circuit breakers, and other components.

2. How Does the Calculator Work?

The calculator uses the following equation:

\( I = \frac{P}{\sqrt{3} \times V \times \text{Cos}\phi \times \text{Eff}} \)

Where:

  • \( I \) is the current (A)
  • \( P \) is the power (W)
  • \( V \) is the voltage (V)
  • \( \text{Cos}\phi \) is the power factor (unitless, between 0 and 1)
  • \( \text{Eff} \) is the efficiency (as a decimal, e.g., 90% = 0.9)
  • \( \sqrt{3} \) is approximately 1.732

Steps:

  • Enter power (P), voltage (V), power factor (Cos φ), and efficiency (Eff)
  • Convert power to watts (W) if necessary
  • Convert efficiency from percentage to decimal
  • Calculate \( I \) using the formula
  • Display the result in amperes (A) or kiloamperes (kA)

3. Importance of 3-Phase Motor Amperage Calculation

Calculating the current drawn by a 3-phase motor is essential for ensuring proper electrical system design, preventing overloads, and selecting appropriate conductors and protective devices.

4. Using the Calculator

Examples:

  • For \( P = 5.5 \, \text{kW} \), \( V = 415 \, \text{V} \), \( \text{Cos}\phi = 0.89 \), \( \text{Eff} = 90\% \):
    • \( I = \frac{5.5 \times 1000}{\sqrt{3} \times 415 \times 0.89 \times 0.9} = 9.55 \, \text{A} \)
  • For \( P = 10 \, \text{hp(I)} \), \( V = 400 \, \text{V} \), \( \text{Cos}\phi = 0.85 \), \( \text{Eff} = 92\% \):
    • \( P = 10 \times 745.7 = 7457 \, \text{W} \)
    • \( I = \frac{7457}{\sqrt{3} \times 400 \times 0.85 \times 0.92} = 13.77 \, \text{A} \)

5. Frequently Asked Questions (FAQ)

Q: What is a 3-phase motor?
A: A 3-phase motor is an electric motor powered by a three-phase alternating current (AC) supply, commonly used in industrial applications due to its efficiency and power.

Q: What are the different horsepower units?
A: Mechanical horsepower (hp(I)) is 745.7 W, metric horsepower (hp(M)) is 735.5 W, and electrical horsepower (hp(E)) is 746 W. These units are commonly used in different regions and applications.

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