Motor Amp Calculator (3 Phase Power)

3-Phase Motor Current Formula:

\[ Current (A) = \frac{Power (kW) \times 1000}{\sqrt{3} \times Voltage (V) \times Power Factor \times Efficiency} \]

Power:

Voltage:

Power Factor:

(0-1)

Efficiency:

(0-1)

Current:

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1. What is 3-Phase Motor Current Calculation?

The 3-phase motor current calculation determines the amperage drawn by an electric motor based on its power rating, supply voltage, power factor, and efficiency. This is essential for proper circuit sizing and protection.

2. How Does the Calculator Work?

The calculator uses the 3-phase power formula:

\[ Current (A) = \frac{Power (kW) \times 1000}{\sqrt{3} \times Voltage (V) \times Power Factor \times Efficiency} \]

Where:

\( Power \) — Motor power rating in kilowatts (kW)
\( Voltage \) — Line-to-line voltage in volts (V)
\( Power Factor \) — Ratio of real power to apparent power (typically 0.8-0.95)
\( Efficiency \) — Motor efficiency as a decimal (typically 0.85-0.95)

Explanation: The formula converts kW to watts, then divides by the product of √3 (for 3-phase), voltage, power factor (accounts for phase difference), and efficiency (accounts for losses).

3. Importance of Current Calculation

Details: Accurate current calculation is crucial for selecting proper wire sizes, circuit breakers, overload protection, and ensuring safe operation of motor-driven equipment.

4. Using the Calculator

Tips: Enter motor power in kW, line voltage in volts, power factor (typically 0.85 if unknown), and efficiency (typically 0.90 if unknown). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical power factor for motors?
A: Induction motors typically have power factors between 0.8-0.9 at full load, lower at partial loads. Synchronous motors can achieve 1.0.

Q2: How does voltage affect current?
A: Current is inversely proportional to voltage. Higher voltage systems draw less current for the same power.

Q3: Why include efficiency in the calculation?
A: Efficiency accounts for energy lost as heat. The actual current drawn will be higher than the theoretical value due to these losses.

Q4: What's the difference between line and phase current?
A: In delta connections, line current = √3 × phase current. In wye connections, line current = phase current.

Q5: How accurate is this calculation?
A: It provides a good estimate for steady-state operation. Actual current may vary with load conditions, temperature, and motor design.