Jiangsu Acrel Electrical Manufacturing Co., LTD.
Jiangsu Acrel Electrical Manufacturing Co., LTD.

What Is Electric Motor Protection Devices? How to Choose?

The purpose of selecting motor protectors is to allow motors to fully utilize their overload capacity, prevent damage, and improve the reliability and continuity of the motor drive system's production. When a simple protector cannot meet the requirements or higher requirements are needed for protection function and characteristics, more complex protectors can be considered. So how to choose an economical and reliable electric motor protection device?

Common types of low-voltage electric motor protection devices

Ordinary type

The structure is relatively simple, and the set current value is set by a potentiometer knob or dip switch. The circuit generally adopts an analog type, and the action protection curve adopts inverse time-limited or timing-limited working characteristics. Its main function is to highlight overload, phase loss (three-phase unbalance), and blockage fault protection. The fault type is displayed by indicator lights, and the running power is displayed by a digital tube.

Digital monitoring type

The internal circuit of the electric motor protection device uses a single-chip microcomputer to achieve the intelligent comprehensive protection of the motor, integrating protection, measurement, communication, and display. The set current is digitally set and can be operated through the buttons on the operation panel. Users can modify and set various parameters on-site according to their actual use requirements and protection conditions. A digital tube is used as the display window. Since the information displayed by the digital tube is not rich enough, this type of protector belongs to the middle and high-end.

Special type

The structure characteristics, basic protection functions, and circuit control methods are roughly the same as the ordinary and digital monitoring types, but the output control wiring method of the protector's internal circuit is different, with a focus on special control, such as fans, pumps, lathes, oil pumps, etc.

Conditions to be considered when selecting electric motor protection devices


First of all, the model specification, motor functional characteristics, protection type, rated voltage, rated current, rated power, power frequency, and insulation must be understood. These contents can provide reference for users on how to correctly use, maintain and select electric motor protection devices.

Environmental conditions

Mainly refers to ambient temperature, high temperature, low temperature, corrosion degree, vibration degree, sandstorms, altitude, electromagnetic pollution, etc.

Motor usage

Mainly refers to the mechanical characteristics required for driving machinery and equipment, such as the mechanical characteristics of different loads, such as fans, pumps, air compressors, lathes, and oilfield pumps.

Control system-related

The control method includes manual, automatic, on-site or remote control, independent operation of a single machine, or a production line chain automation program, and there are many starting methods such as direct start, reduced voltage start, star-delta start, frequency-sensitive variable resistor, inverter, and soft start.

Other aspects

Whether the user's on-site production monitoring and management is more arbitrary or rigorous, and the severity of the impact of abnormal shutdown on production, etc.

There are many factors related to the selection of electric motor protection devices, such as the installation position, connection lines, and the coordination of electrical equipment in the system. However, the main factors are the degree of impact of changes in the motor's operating conditions and control changes on production. Based on the actual changes in the above-mentioned actual working conditions, a protector should be selected and adjusted reasonably.