What is a Motor Protection Circuit Breaker (MPCB)

What is a Motor Protection Circuit Breaker (MPCB)


Have you been looking for a perfect solution for the smooth working of electric motors? 

Well, here’s everything you need to know, in a single place!

You wouldn’t like to spend money repairing and even replacing the motors due to overload and short circuit.

What is a Motor Protection Circuit Breaker?

Protecting an electric motor from such any issues is no more a problem. Because you have an electromechanical device like Motor Protection Circuit Breaker, this device has become a must component because it automatically disconnects the circuit if an overload or current fluctuations occur. In addition, MPCB comes equipped with a thermal delay that cools down the motor. 

Electric motors are essential for even everyday tasks in today’s world. Thus, to make them function smoothly and protect them from any faults, you would need MPCB. The industrial and commercial areas where MPCB’s application becomes essential are:

  • Elevators and other hoisting devices.
  • Heat Pumps, rooftop air conditioners, cooling towers, compression, chillers, etc.
  • Industrial conveyor belts.
  • Injection and extraction fans
  • Air handling units

To further make you realize the importance of Motor Protection Circuit Breaker, we have gathered all the information about the functioning, working principles, and many other aspects of this device.

Let’s proceed with the discussion.

Short Circuit Protection

The short circuit is the most frequently occurred problem caused when two phases contact one another. Or it may also be caused by the contact between the phase and earth conductor. To get your motor rid of such a problem, you would need a protection device like MPCB.

It would be best if you considered while choosing a protection device that its breaking capacity must be greater than a short circuit current. That is calculated in the point of the system. Breaking capacity, in this regard, is the characteristic of specific devices that allows you to open electric circuits such as fuses, motor protection circuit breakers, and switch disconnectors. 

Phase Loss Protection

Phase loss causes motor blowers, pumps, and other equipment to gain excessive current when one phase of the three-phase system is lost. Loss of such type occurs due to thermal overload, worn contact, blown a fuse, or mechanical failure.

Thus, to increase the level of reliability, you would require MPCB. If phase loss is kept unchecked, it can result in equipment failures, costly downtime, or other unsafe conditions. MPCB assures the safety of motors from burning of the windings.

Protection against Overload

The smooth functioning of the motor could be interrupted by the conditions like; the jamming of the rotors, too frequent starting, high resistance torque, or loss of one of the three system phases. Such conditions result in overloading that causes the motor to overheat. 

The built-in thermal relay of MPCB can regulate the tripping current. It can cover a range of motors having a nominal current from 0.1 A to 100 A. Its development is such that it makes it possible for you to view the value of the thermal release. Not just this, but your motor gets safe from voluntary or accidental tampering. 

Now that you have grasped an overview of the importance of a protection device. It’s time for you to get familiar with MPCB so that you could make motors reliable and make them work smoothly.

That isn’t all about MPCB. We have got much more.

Keep scrolling!

What is an MPCB?

A Motor Protection Circuit Breaker takes every best measure possible to provide the motor with fuseless protection. It is capable of switching off the motor if it detects any threat to prevent damage. In addition, MPCB comes equipped with a thermal delay that cools down the motor. 

To get you updated about the fault signalling, MPCB comes with an LED display that turns ON every time MPCB trips. This feature allows you to beware of the fault that occurred to the motor. This protection device has been used widely for both dynamic and static electric equipment. 

Construction of an MPCB

A Motor Protection Circuit Breaker contains five parts: magnetic trip, auxiliary switches, thermal overload release, the main contact, and Enclosure. .  

  1. Magnetic Trip: 

A magnetic trip is a mechanism that protects the motor from short circuit faults. 

  • Auxiliary switches

Auxiliary switches are the switches that enable the MPCB status to be sent to external circuits.

  • Thermal Overload Release: 

Thermal overload release protects against a high balanced current by limiting the current flow to the motors. Thermal overload release becomes functional when the electric current becomes higher in value than the preset value.

  • Main contact 

The main contact of the Motor Protection Circuit Breaker enables the flow of current from the source to load circuits. It comprises moving contacts and two-part fixed contacts.

  • Enclosure: 

The Enclosureis used to cover the inner mechanism of the protective device. It a component made from plastic resins. The strength of the Enclosure increases by adding fillers to the plastic resin.

Working Principle of MPCB

We have gone through the construction of a Motor Protection Circuit Breaker. The next thing that becomes important to consider is its working principle. We could get an idea from the components of MPCB that it is the subtype of the thermal-magnetic circuit breaker. However, MPCB comes featured with additional functions for the efficient protection of motors. 

MPCB comes equipped with a manual interruption mechanism. This feature allows you to disconnect the electric motor for maintenance and replacement. In addition, magnetic protection utilized by MPCB protects the motor against a line fault, short circuit, or other electric faults. The dangerous fault currents are disconnected immediately by the instantaneous functioning of magnetic protection.  

The thermal protection of MPCB protects the motor against overload. In case of excessive current, the motor disconnects by the expanding and contracting contact. MPCB contains a magnetic coil that works such that, is high electric current flows through these coils, the armature enclosed by the coil receives a force. That unlocks the loaded switch latch, which causes it to release the stored spring energy. This course of the event opens the main contact and disconnects the overflow of electric current. 

It becomes necessary to mention that motor protection circuit breakers are available with a variety of current ratings. Their noticeable feature is that you get to adjust the current ratings in most of the models. That is to say that MPCB could provide protection even from different capacities.


Motor Protection Circuit Breaker and Moulded Case Circuit Breaker are the devices used widely to interrupt the circuit automatically in case of faults. In addition, both are used to protect the motor against short circuits or overload. However, when it comes to applications, both these devices are entirely different. 

MPCB is designed especially for motor protection.MCCB is designed for general circuit protection.
MPCB doesn’t require a relay for its functioning.MCCB does require a relay for its functioning.
MPCB could be turned ON or OFF manually.MCCB requires contractors for this purpose.
MPCB comes equipped with the auto-resetting feature that enables the motor to resume its operation over a period.MCCB doesn’t have any such feature.

There are plenty of other differences that make MPCB more efficient in its application when compared to MCCB.

Advantages of an MPCB

  • Motor Protection Circuit Breaker comes in a compact size.
  • You get to save the motor from phase loss, short circuit, over-current, and other under-voltage faults just by a single device.
  • You wouldn’t require any external overload relay.
  • It comes with easy adjustments.
  • MPCB would require less maintenance.
  • The adjustable strips of MPCB for overload protection are bimetallic.
  • You get to set the maximum load current based on the full load current of the motor.

Disadvantages of MPCB

  • Its high cost makes it beyond the reach for those who are budget conscious.
  • It restricts you from setting a short circuit current tripping limit.
  • MPCB cannot be repaired. 

Selection Guide for MPCB

Now that you have a lot of knowledge about MPCB, you probably would have made your mind to go for one. In this regard, you would be required to keep certain factors in your mind so that MPCB could serve useful in the best possible way.

  • Frequency is the first factor that you need to consider while choosing the MPCB for motors. 
  • You need to buy the device whose voltagerating matches the nameplate voltage of the motor.
  • Check for the optimal short circuit performance. 
  • Analyze the interrupting capacity.
  • The tripping behavior should be efficient.
  • Check the sensitivity to phase failure.

If you are not experienced with circuit breakers and all that, you could consent to a certified electrician.


We have had a detailed discussion about Motor Protection Circuit Breaker. The role MPCB plays in electrical safety is quite evident. Usually, MPCB is used for low voltage motors. That is because it provides multiple types of protection and doesn’t require any additional relays.

Hence these are the best choices you have for motors of any type, whether commercial or industrial. With the Right protection device, you could save yourself from any costly repairs.

The fact that motor ratings are declared on the product makes MPCB an easier protection device. Not just this, but MPCB recommends because its operating life is longer than any other device in the market. With the provided details, you won’t have any second thoughts about the efficiency of MPCB.


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