Here’s Everything You Need to Know About Motor Protection Circuit Breakers

A Motor Protection Circuit Breaker (MPCB) is an electromechanical device which protects a motor against fluctuations in current, overload, and unscheduled or sudden interruptions in the main electric circuit. Additionally, it offers protection against phase imbalance or loss and line faults in 3-phase motors. MPCBs help in saving costs and space and provide fuseless protection, which switches off the motor instantly to prevent it from damage. It also disconnects the current safely in case of short circuits. Furthermore, MPCB is typically equipped with thermal delay for allowing electric motors to cool. Now, let’s understand the difference between motor circuit protectors and MPCBs. 

Difference Between Motor Circuit Protectors and Motor Protection Circuit Breakers

The two reasons behind the occurrence of excess current are short circuits and overloads. 

Overloads can possibly occur when the electrical equipment draws marginally more current, which might even build up over time. Usually, overloads don’t cause any damage whenever they occur for the first time. In contrast, short circuits usually occur rapidly, which can generate currents over full rated loads. Therefore, it is important to deal with short circuits immediately. 

There is a minor difference between a motor protection circuit breaker and a motor circuit protector. A motor circuit protector is a distinct type of circuit breaker which protects motors from short circuits. When you use a motor circuit protector, installing an overload relay is important to protect the motor against overloads. 

Motor circuit protectors are commonly used in Motor Control Centre assemblies in industries, where multiple components are integrated together, and space isn’t an issue. The motor circuit protector is generally designed with magnetic settings that are adjustable, allowing the operator to set the magnetic protection level of a breaker just above the motor’s inrush level. The motor’s overload protection is supplied in the overload relay of a starter. 

Generally, motor circuit protectors are utilised in branch circuits, whereas motor protection circuit breakers are widely used in feeder circuits. However, in low-voltage switchgear, generally, MPCBs are used because they do not require additional relays and combine the protection of both types in one single thermal-magnetic circuit breaker. They even reduce the reset time right after an overload or short circuit, which reduces the overall downtime. In addition, MPCBs come in a variety of settings and sizes, which allows significant flexibility during installation. 

How Does an MPCB (Motor Protection Circuit Breaker) Work?

A Motor Protection Circuit Breaker has three significant functions, especially designed for electric motors’ protection. 

• MPCB’s thermal protection safeguards the electric motor against overload. A contracting and expanding contact will eventually disconnect the electric motor in case it detects excess current. For allowing the high inrush currents that occur when a motor starts, a delayed response is in-built. However, if the inrush current is extended for a longer period and the motor doesn’t start, it results in tripping of thermal contact.
• Magnetic protection safeguards against short circuits and severe electrical faults as it disconnects the current as and when there is fault detection. 
• Phase protection safeguards against phase imbalance or loss. 3-phase circuit motors are able to function efficiently with balanced or equitable voltages in their 3 live conductors. An imbalance of more than two percent in the phase voltage reduces the service life and efficiency of the motors, and sudden or unexpected loss of any of the phase voltages might damage it further. In this case, the motor might run continuously; however, the current flow might exceed the rated value in the other two phases. Additionally, this might even burn the motor windings. A motor protection circuit breaker keeps measuring the variation in phase voltages and disconnects the motor immediately if any imbalance or loss occurs. 

As motor circuit protectors and motor protection circuit breakers have a crucial role to play, it is important to choose an appropriate one as per the scope of your application. Therefore, it is advisable to get in touch with expert professionals who can assist you in making the right choice, helping you reduce downtime and enhance motor efficiency.