3-Phase Motor Amperage Calculator

Created by Kenneth Alambra
Reviewed by Madhu Raman
Last updated: Mar 30, 2022

This 3-phase motor amperage calculator will help you determine the amperage or the full load current needed to run any 3-phase motor depending on its power rating, motor voltage, power factor, and efficiency.

In this calculator, you will learn:

  • What a 3-phase motor is;
  • How to calculate a 3-phase motor current requirement; and
  • The importance of knowing what a 3 phase motor's amperage is.

This tool can also work as a motor efficiency calculator. Motors age and wear in time due to usage, affecting its performance. Keep on reading to start learning.

What is a 3-phase motor?

A 3-phase motor is an electric motor that runs on a 3-phase alternating current (AC) power. We use this kind of motor in hydraulic pumps, compressors, and other industrial machinery that requires high power or angular velocity. Inside a 3-phase motor is a series of electromagnets that interact with each other resulting in the rotational motion of the motor's rotor.

When powering a 3-phase motor, we would want to follow its specifications printed on its motor rating plate. The motor rating plate indicates how much power and voltage would run the motor, how efficient it is in translating the input power to output power, and even how much amperage it could allow. If we do not follow these specifications, we take the risk of overheating or even burning the motor. We could also end up using the wrong wire sizes when connecting to its power supply.

However, sometimes, the motor rating plate is incomplete or tampered with, especially for old and used motors. This is where our 3-phase motor amperage calculator turns out to be of use. Before we learn how to calculate the 3-phase motor current, let's first learn how to use this calculator in the next section of this text.

How to use this 3-phase motor amperage calculator?

Our 3-phase motor amperage calculator has some default values that you can change depending on your requirements. To use our tool to find the amperage of a typical 3-phase motor:

  1. The first step is to enter the motor voltage of your motor.
  2. Then, input its power rating. Choose the unit of measure that matches the motor rating plate.
  3. Type in both your motor's power factor and efficiency. If your motor rating plate doesn't show the power factor, you can approximate it by entering a value from 0.80 to 0.98 - which is the range of a typical 3-phase motor power factor. On the other hand, the typical value for efficiency is from 75% to 95%.

After entering these values, our 3-phase motor amperage calculator will instantly display your motor's estimated amperage or full load current.

On the other hand, if your motor rating plate has all the parameters provided except the motor efficiency, you can find its value by leaving it empty and entering all the other information you have. Newer motors tend to have higher efficiencies as we discover and implement new technology. Having a high-efficiency motor means that less electricity goes to waste.

Now that we know how to use this calculator, how about we discuss how to calculate the full load current of a 3-phase motor? 🙂

✅ You can also use this tool for single-phase motors. Simply choose Single phase on the Load distribution parameter to calculate 🙂.

How to calculate a 3-phase motor current requirement

To calculate how much current flows through the motor, we can use the concept of Ohm's Law, where the strength of the electric current flowing through a system is equal to the power applied divided by the voltage, expressed in equation form as shown below:

I = P / V

However, for 3-phase systems, we apply a voltage multiplier equal to √3 for line-to-line voltage configuration, and 3 for line-to-neutral. For 3-phase motors, we also divide the power rating by the power factor and efficiency. In equation form, we have:

For 3-phase line-to-line configuration

  • I = P / (√3 × V × cos Φ × η)

For 3-phase line-to-neutral

  • I = P / (3 × V × cos Φ × η)

where:

  • I - Full load current or amperage (Amperes);
  • P - Real power required to power the motor (Watts);
  • cos Φ - Power factor of the motor;
  • V - Voltage needed to for the motor to work (Volts); and
  • η - Efficiency of the motor (%).

🔎 If the power rating provided in the motor rating plate is in horsepower (hp), we can multiply it by 746 to convert the power rating to watts.

Since we also cover single-phase motors in our calculator, here is the formula for that:

For single-phase load distribution

  • I = P / (V × cos Φ × η)

Now that we know how to calculate the full load current of 3-phase motors, why not check our other related calculators?

FAQ

How do I calculate the full load current of a 3-phase motor?

To calculate the full load current or the amperage of a 3-phase motor,

  1. First, know your motor's specifications including the power rating (P), voltage requirement (V), power factor (cosΦ), and efficiency (η).
  2. If P is in kW, use this equation: amperage = 1000 × P / (1.73205 × V × cosΦ × η).
  3. If P is in hp, using this equation: amperage = 746 × P / (1.73205 × V × cosΦ × η).
  4. Substitute the corresponding values of your motor's specifications to find the full load current in amperes.

How many amps does a 2 hp 3-phase motor use?

Let's say we have a 2-hp 3-phase motor with a motor voltage of 230 V, a power factor of 0.85, and an efficiency of 95%. We can calculate its amperage using this equation: amperage = power rating × 746 / (1.73205 × motor voltage × power factor × efficiency). By substituting each parameter's values, we have amperage = 2 hp × 746 / (1.73205 × 230 V × 0.85 × 95%). Which results in amperage = 4.638 amperes

How do I calculate a 3-phase motor horsepower?

You can use this equation HP = amperage × motor voltage × power factor × efficiency × 1.73205 / 746 to calculate the power rating of a 3-phase motor in horsepower. Make sure to use values for amperage in amperes, the motor voltage in volts, and efficiency in percentage to calculate the power rating in horsepower correctly.

Kenneth Alambra
Load distribution
3-phase
Voltage type
Line to Line Voltage
Motor voltage (V)
V
Motor power rating (P)
kW
Power factor (cos Φ)
Motor efficiency (η)
%
Amperage (I)
A
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