Motor protection circuit breakers (MPCB)

Motor protection switches, explained in simple terms

Motor protection switches, also known as Motor Protection Circuit Breakers (MPCBs), are electromechanical switches with which motors can be switched on and off. They are used primarily for the monitoring of 3-phase motors.

During ongoing operation, the switches are used mainly for the protection of motors against thermal and electronic overload, which would otherwise result in motor damage. This is achieved by means of the monitoring of the absorbed current, using thermal, mechanical, thermal-electrical, or electronic processes.

If the thermal-mechanical principle is adopted, the process is comparable to the function of a bimetal thermometer. When heated, the metal integrated into the inside of the switch bends and, from a certain length, touches the trigger, which causes the motor protection switch to switch off.

With the thermal-electrical variant the behaviour is similar, except that here the temperature of the current sensor is monitored. When a pre-defined temperature value is reached, a bimetal strip or a temperature sensor is activated, which switches off the drive.

With an electronic process, the flow of current through the sensors is monitored and the switching off of the drive is induced as soon as a specified threshold value has been exceeded.

After correcting the causes of the fault, the motor can be manually switched on again.

Some motor protection models have padlocks on the rotary handle, which prevent unintentional reactivation.

Motor protection switches are also referred to as circuit breakers, as they are now not necessarily used solely for motor protection, but can also perform other functions.

For example, the switches can be used for general system protection against short circuits and phase failures and as a means to disconnect from the power supply in order to safely perform maintenance work. In addition, they can also be used to monitor the failure of the motor to start up and to perform switching operations, which is particularly applicable with machines that are only seldom switched on and off.

In summary, a differentiation can be made between circuit breakers for motor protection with integrated overload monitoring, that is, motor protection switches in the true sense, circuit breakers for transformers, and circuit breakers for starter combinations for simple protection against short circuits.

Where are motor protection switches used?

Motor protection switches are essential in almost all industries, in order to control motors and protect them against damage. For example, they are used in the following areas:

• Energy technology
• Water and sewage services
• Oil and gas industry
• Building technology

With products from Siemens & Schneider Electric, Automation24 supplies motor protection to suit your needs

In the Automation24 online shop, you can purchase motor protection switches from the reputable manufacturers Siemens and Schneider Electric, available within the Protection Technology product range.

Siemens SIRIUS motor protection switches are available in the sizes S0 and S00, with rotary controls and spring-clamp terminals or screw connections. Depending on the specific switch design, the operating current at AC-3 400 V is between 0.16 A and 40 A.

The motor protection switches can be optimally combined with Siemens components from the SIRIUS modular system, such as contactors, overload relays, and soft starters, which are also available in the shop.

On the other hand, if you use Schneider Electric motor protection, you can find circuit breakers in the TeSys Deca size, with rotary knob or pushbutton operation in the product range. Here, the operating current range at AC-3 400 V ranges from 0.16 A to 32 A, depending on the product variant.

Schneider Electric motor protection switches are ideally used in combination with other modules from the TeSys Deca switching and protection equipment series.

In addition, you can also find compatible accessories for circuit breakers and industrial enclosures for the operation and protection of motor protection switches at Automation24.