3 Phase Motor Current Calculator

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 the 3-Phase Motor Current Formula?

The 3-phase motor current formula calculates the current drawn by a three-phase AC motor based on its power rating, supply voltage, power factor, and efficiency. This is essential for proper motor sizing and electrical system design.

2. How Does the Calculator Work?

The calculator uses the 3-phase motor current 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 (0-1)
\( Efficiency \) — Motor efficiency as a decimal (0-1)

Explanation: The formula accounts for all three phases of power delivery and converts kW to watts (×1000). The √3 factor comes from the relationship between line and phase voltages in a 3-phase system.

3. Importance of Current Calculation

Details: Accurate current calculation is crucial for selecting proper wire sizes, circuit breakers, overload protection, and ensuring the electrical system can handle the motor's starting and running currents.

4. Using the Calculator

Tips:

Power: Typically found on motor nameplate (in kW or converted from HP)
Voltage: Line-to-line voltage (e.g., 208V, 230V, 460V, 480V)
Power Factor: Typically 0.8-0.95 for motors (0.85 default)
Efficiency: Typically 0.85-0.95 for modern motors (0.90 default)

5. Frequently Asked Questions (FAQ)

Q1: How do I convert HP to kW for the formula?
A: Multiply HP by 0.746 to get kW (1 HP = 0.746 kW).

Q2: What's the difference between line and phase voltage?
A: In 3-phase systems, line voltage is between any two lines, while phase voltage is between any line and neutral.

Q3: Why is power factor important?
A: Lower power factor means more current is required to deliver the same real power, increasing system losses.

Q4: How does motor efficiency affect current?
A: Less efficient motors draw more current to deliver the same output power.

Q5: What about motor starting current?
A: Starting current (inrush) is typically 5-7 times running current but lasts only briefly during startup.