Small 3 Phase Electric Motor Calculator

Current Formula:

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

Current (amps):

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1. What is a Small 3 Phase Electric Motor Calculator?

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

Purpose: It helps electricians and engineers determine the current requirements for small three-phase motors (typically under 5 kW).

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)
\( V \) — Voltage (volts)
\( PF \) — Power factor (unitless, typically 0.8-0.9)

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

3. Importance of Current Calculation

Details: Proper current estimation ensures correct wire sizing, circuit breaker selection, and protection device settings for motor circuits.

4. Using the Calculator

Tips: Enter the motor power in kW, line voltage (default 400V), and power factor (default 0.85). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is √3 used in the formula?
A: The √3 factor accounts for the phase difference in three-phase systems, converting between line and phase quantities.

Q2: What's a typical power factor for small motors?
A: Most small three-phase motors have power factors between 0.8 and 0.9 at full load.

Q3: Does this work for large motors?
A: While the formula is valid, large motors may have different characteristics and efficiency considerations.

Q4: How do I find the motor power rating?
A: Check the motor nameplate which typically shows kW or HP (1 HP ≈ 0.746 kW).

Q5: Should I use line-to-line or line-to-neutral voltage?
A: Always use line-to-line voltage (typically 400V, 480V, etc.) for three-phase calculations.