Enter the power (kW), the voltage (volts), the efficiency factor, and the power factor into the calculator to determine the Motor Current. 

Motor Current Formula

The following formula is used to calculate the Motor Current.

Im = 1000 * P / [ SQRT(3) * V * EF *PF ] 
  • Where Im is the Motor Current (amps)
  • P is the power (kW) 
  • V is the voltage (volts) 
  • EF is the efficiency factor 
  • PF is the power factor

To calculate a motor current, multiply the power by 1000, then divide by the product of 1.732, the voltage, efficiency factor, and power factor.

How to Calculate Motor Current?

The following example problems outline how to calculate Motor Current.

Example Problem #1

  1. First, determine the power (kW). In this example, the power (kW) is determined to be 67 .
  2. Next, determine the voltage (volts). For this problem, the voltage (volts) is measured to be 20 .
  3. Next, determine the efficiency factor. In this case, the efficiency factor is found to be 5.
  4. Next, determine the power factor. This is .85.
  5. Finally, calculate the Motor Current using the formula above: 

Im = 1000 * P / [ SQRT(3) * V * EF *PF ] 

Inserting the values from above and solving yields: 

Im = 1000 * 67 / [ SQRT(3) * 20* 5 *.85 ]  = 455.08 (amps)

FAQ

What is the significance of the efficiency factor in calculating motor current?

The efficiency factor represents how well the motor converts electrical energy into mechanical energy. A higher efficiency factor indicates a more efficient motor, which requires less electrical current to produce the same amount of mechanical power. This factor is crucial in calculating motor current because it directly impacts the amount of current the motor draws from the power source.

How does the power factor affect the motor current calculation?

The power factor is a measure of how effectively electrical power is converted into useful work output. It ranges between 0 and 1, with values closer to 1 indicating more efficient power use. A lower power factor means the motor requires more current to deliver the same amount of power, making it an essential variable in calculating motor current. It reflects the phase difference between the voltage and current waveforms, affecting the overall efficiency of the motor’s operation.

Can the motor current formula be used for both AC and DC motors?

While the provided formula primarily applies to AC motors due to the inclusion of the power factor and the square root of 3 (which relates to three-phase power), variations of this formula or different formulas altogether may be used for DC motors. For DC motors, the calculation is often more straightforward, focusing on the direct relationship between power, voltage, and current without the need for power factor or efficiency factor adjustments. However, understanding the specific requirements and characteristics of the motor in question is essential for accurate calculations.