Understanding Three-Phase Motors

Three-phase motors are commonly used in large pump applications, such as those affiliated with agriculture and manufacturing operations, as opposed to the single-phase motors typically found in residential and light-non-industrial applications.

Single phase power is not recommended for use on motors greater than 5HP because a single-phase motor draws significantly higher current than a three-phase motor of the same horsepower rating. Based on cost, single-phase motors are less efficient compared to three-phase, increasing operational costs.

For larger applications requiring efficiency and consistency, a three-phase motor is the best option. The advantages to using a three-phase motor include:

  • Energy savings, as three-phase motors use up to 90% less power to do the same work as a single-phase motor and can turn over the same amount of water at a lower pump speed. Three-phase motors can transmit three times the amount of power of a single source, while using only 1.5 times the amount of conducting wires.
  • Three-phase motors provide smooth, balanced power. The consistency in the supply of power is due to three identical overlapping wave cycles, which are evenly spaced 120 degrees apart, so the supplied power remains constant.
  • The constant power potential is not only preferable, but necessary in many situations where the business, farm, or factory needs and depends on consistent power.
  • Three-phase motors can run at a higher voltage with thinner gauge wire due to the lower amperage used. The lower pump speed and reduced friction also produces less stress and cooler temperatures for other components. Plus, there is less vibration, reducing stress on pipes.
  • A three-phase motor water pump has a simple design and smaller body size, also resulting in cost savings. Their reliability and longer life span also extends the pump replacement interval.

Important Installation Note — Check the Pump’s Rotation

One critical factor that must be adhered to after the power is supplied and before the pump is lowered into the basin is to check the pump’s rotation so the performance desired is achieved and no damage occurs. Not to mention the time and energy required to reverse the issue after the fact.

Three-phase power is easily wired to run a pump in reverse; the motor can run forward or backwards (clockwise and counter-clockwise). Even with running backwards (or in the wrong direction), the pump will still function – and pump water, but this type of misuse will eventually cause pump/motor failure.

Three-phase pumps have stickers, engravings, or casted directional arrows indicating the rotation direction when looking at the entire pump/motor assembly. To test, give the pump a quick bump of power and check that the impeller is rotating in the same direction as the arrow. If a three-phase motor rotates in the wrong direction, you can swap any two leads to change the desired direction. Just make sure you test the motor again before installing and note the terminal/wire color combination as well.

With installations where more than one pump is being installed, rotation must be checked on each pump. Do not assume the color coded wires from the pump are the same – they typically are but not always.

If you have questions on this or the rest of your application, the pros at JMI Pump Systems are ready to help. Your Partners in Pumping since 1958 are available to assist you at 262-253-1353 or sales@jmipumps.com.

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