Electronic solid state phase protector has been around for some time now with the advancement in the semiconductor technology. It has enabled the design of this device that is used as part of the motor controls. They are accessory devices that designers used to protect the motors from premature failure due to voltage faults.

In the field of HVAC, these devices are used to protect large three phase fan motors and compressor motors from being damaged.

Phase Protector Features

Check the specifications for the features that are being offered as they varies from one manufacturer to another. Here are some of them that you will want to consider.

Undervoltage & Overvoltage

Motors operate the best when the input voltages are within the specifications with a small tolerance. Undervoltage will reduce the torque in starting up the motor, increase in current flow and eventually causing heat to build up in the windings. This will cause the insulation of the windings to breakdown hence decreasing the lifetime of the motors.

When overvoltage occurs due to a fault in the incoming power supply, the motor will go into saturation causing high current to flow and eventually damage the windings of the motors.

Check that the devices are able to protect the motors when this happen.


A 3-phase monitor from ICM Controls

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Phase Reversal

The three-phase motors will rotate in the reverse direction when the phases of the power supply are reversed. This will cause improper operation to the compressors in particular the rotary, scroll and centrifugal compressors. Having this protection is necessary in the design of these systems.

Phase Loss

All the three phases to the motor must be present or else it will overload. If one phase is loss, the device will stop the power to the motor and alert the user through the indicators on the phase protector.


It is always necessary to ensure that there is a certain minimum duration that has elapsed before the motors can start again. This is critical for large motors as it is usually not designed to restart immediately. A time duration of a few minutes is usually recommended by the manufacturers or the designers. Having this feature in the device will help to ensure the lifetime of the motor is protected.

Voltage Imbalance

When the 3-phase power supply voltage from the utility company is not balanced or an unbalanced happens that is caused by the load in the building, it will cause the motor to overheat and damage the windings.

The imbalance voltage usually can be set and the recommended value is usually below 2%.

Editorial Contributors
Alora Bopray

Alora Bopray

Staff Writer

Alora Bopray is a digital content producer for the home warranty, HVAC, and plumbing categories at Today's Homeowner. She earned her bachelor's degree in psychology from the University of St. Scholastica and her master's degree from the University of Denver. Before becoming a writer for Today's Homeowner, Alora wrote as a freelance writer for dozens of home improvement clients and informed homeowners about the solar industry as a writer for EcoWatch. When she's not writing, Alora can be found planning her next DIY home improvement project or plotting her next novel.

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Roxanne Downer


Roxanne Downer is a commerce editor at Today’s Homeowner, where she tackles everything from foundation repair to solar panel installation. She brings more than 15 years of writing and editing experience to bear in her meticulous approach to ensuring accurate, up-to-date, and engaging content. She’s previously edited for outlets including MSN, Architectural Digest, and Better Homes & Gardens. An alumna of the University of Pennsylvania, Roxanne is now an Oklahoma homeowner, DIY enthusiast, and the proud parent of a playful pug.

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