3 Phase Motor Current Calculation Formula

3-Phase Motor Current Formula:

\[ I = \frac{P_{kW} \times 1000}{V \times PF \times \sqrt{3}} \]

Motor Current (amps):

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1. What is 3-Phase Motor Current Calculation?

Definition: This calculator determines the current drawn by a three-phase electric motor based on its power rating, supply voltage, and power factor.

Purpose: Essential for electrical engineers and technicians to properly size circuit breakers, wires, and protection devices.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ I = \frac{P_{kW} \times 1000}{V \times PF \times \sqrt{3}} \]

Where:

\( I \) — Current (amps)
\( P_{kW} \) — Motor power (kilowatts)
\( V \) — Line voltage (volts)
\( PF \) — Power factor (0.1 to 1)

Explanation: The formula converts kW to watts (×1000), divides by the product of voltage, power factor and √3 (1.732) for three-phase systems.

3. Importance of Motor Current Calculation

Details: Accurate current calculation prevents electrical hazards, ensures proper equipment selection, and maintains system efficiency.

4. Using the Calculator

Tips: Enter motor power in kW, line voltage (default 400V for many industrial systems), and power factor (default 0.85 for motors).

5. Frequently Asked Questions (FAQ)

Q1: Why is √3 used in the formula?
A: √3 (approximately 1.732) accounts for the phase difference in three-phase systems.

Q2: What's a typical power factor for motors?
A: Induction motors typically have 0.85 PF at full load, but this varies with load and motor type.

Q3: How does voltage affect current?
A: Higher voltage means lower current for the same power, following Ohm's Law (P = VI√3×PF).

Q4: Should I use line or phase voltage?
A: Use line-to-line voltage (e.g., 400V for 400Y/230V systems).

Q5: Does this account for motor efficiency?
A: No, this is input current. For output power, divide by efficiency if known.