Amp Calculator 3 Phase Motor

Three Phase Motor Amps Formula:

\[ I = \frac{HP \times 746}{V \times \sqrt{3} \times PF \times Eff} \]

Horsepower (HP):

Voltage (V):

volts

Power Factor (PF):

(0-1)

Efficiency (Eff):

(0-1)

Current (Amps):

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1. What is the Three Phase Motor Amps Formula?

The three phase motor amps formula calculates the current drawn by a three-phase motor based on its horsepower rating, operating voltage, power factor, and efficiency. This calculation is essential for proper electrical system design and motor protection.

2. How Does the Calculator Work?

The calculator uses the three phase motor amps formula:

\[ I = \frac{HP \times 746}{V \times \sqrt{3} \times PF \times Eff} \]

Where:

\( I \) — Current in amperes (A)
\( HP \) — Horsepower rating of the motor
\( V \) — Operating voltage (volts)
\( \sqrt{3} \) — Mathematical constant (approximately 1.732)
\( PF \) — Power factor (dimensionless, 0-1)
\( Eff \) — Motor efficiency (dimensionless, 0-1)
746 — Conversion factor from horsepower to watts

Explanation: The formula converts horsepower to electrical power (watts), then calculates the current based on the three-phase power equation, accounting for power factor and efficiency losses.

3. Importance of Current Calculation

Details: Accurate current calculation is crucial for proper wire sizing, circuit breaker selection, motor protection device setting, and ensuring the electrical system can handle the motor's starting and running currents.

4. Using the Calculator

Tips: Enter horsepower as a positive number, voltage in volts, power factor and efficiency as decimal values between 0 and 1. All values must be valid and greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: Why is the 746 factor used in the formula?
A: 746 watts equals 1 horsepower, so this factor converts mechanical horsepower to electrical watts for power calculation.

Q2: What is a typical power factor for three-phase motors?
A: Power factor typically ranges from 0.8 to 0.9 for most industrial motors at full load, but can be lower at partial loads.

Q3: How does motor efficiency affect current draw?
A: Higher efficiency motors draw less current for the same power output, as less electrical energy is wasted as heat and other losses.

Q4: Why is the √3 factor used for three-phase calculations?
A: The √3 factor accounts for the phase relationship in three-phase systems, where the line-to-line voltage is √3 times the phase voltage.

Q5: Should this calculation be used for motor starting current?
A: No, this formula calculates running current only. Starting current (inrush current) is typically 5-7 times higher than running current and requires separate calculation.