Motor kW to Amps Calculator (Three Phase)

Three Phase Current Calculation:

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

Power (kW):

Voltage:

Power Factor:

(0-1)

Efficiency:

(0-1)

Current:

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1. What is Three Phase Current Calculation?

The three-phase current calculation determines the electrical current drawn by a three-phase motor based on its power rating, supply voltage, power factor, and efficiency. This is essential for proper circuit design and protection.

2. How Does the Calculator Work?

The calculator uses the three-phase current formula:

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

Where:

\( kW \) — Motor power rating in kilowatts
\( Voltage \) — Line-to-line voltage in volts
\( Power\ Factor \) — Ratio of real power to apparent power (0-1)
\( Efficiency \) — Motor efficiency (0-1)
\( \sqrt{3} \) — Constant for three-phase systems (≈1.732)

Explanation: The formula converts kW to watts (×1000), then divides by the product of voltage, square root of 3 (for three-phase), power factor, and efficiency to get current in amperes.

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 electrical equipment.

4. Using the Calculator

Tips:

Enter motor power rating in kW (nameplate value)
Use line-to-line voltage (typically 400V for 380V systems due to voltage drop)
Typical power factor: 0.85 for motors
Typical efficiency: 0.9 (90%) for standard motors

5. Frequently Asked Questions (FAQ)

Q1: Why multiply by 1000 in the formula?
A: The formula converts kilowatts (kW) to watts (W) since voltage is in volts and current in amperes.

Q2: What's the difference between line and phase voltage?
A: In three-phase systems, line voltage is between two lines, while phase voltage is between line and neutral. The calculator uses line voltage.

Q3: How does power factor affect current?
A: Lower power factor increases current for the same real power. Improving power factor reduces current draw.

Q4: What if I don't know the efficiency?
A: For estimation, use 0.9 (90%) for standard motors. High-efficiency motors may have 0.93-0.96.

Q5: Can I use this for single-phase motors?
A: No, single-phase motors use a different formula without the √3 factor.