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Motor Protection Circuit Breaker or MPCB

Published on 24/2/2012 & updated on 30/8/2018
Page Description: Learn what a motor protection circuit breaker is, motor protection circuit breaker working principle, chart, sizing (selection guide) and etc.
Motor protection circuit breakers are a specialized type of electrical protection device that is designed specifically for electric motors, like their name implies. Electric motors have plenty of applications and are used to drive mechanical devices of all types, so it is very important to protect them adequately with MPCBs. The following are just a few examples of devices driven by electric motors in commercial and industrial buildings: In all of these industrial and commercial applications of electric motors, the MPCB has the key role of providing electrical protection. motor protection circuit breaker

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Motor Protection Circuit Breaker or MPCB

What is a Motor Protection Circuit Breaker and what are its Functions?

A motor protection circuit breaker, or MPCB, is a specialized electromechanical device that can be used with motor circuits of both 60 Hz and 50 Hz. It has several functions that allow it to provide a safe electrical supply for motors:

Motor Protection Circuit Breaker Working Principle

The motor protection circuit breaker can be considered a subtype of thermal magnetic circuit breaker, but with additional functions that are specially designed to protect electric motors. The basic working principle is similar to all other circuit breakers.

Asynchronous Motor Protection

Most motors used in the industry are a asynchronous motors, also known as squirrel-cage induction motors. These motors use three-phase power to create a rotating magnetic field, which in turn magnetizes the rotor an creates rotational movement. When designing the electrical protection for an asynchronous motor and selecting motor protection circuit breakers, there are some very important factors to consider that aren’t present when protecting other types of electrical circuits. Then, what kinds of breakers can be used for the protection of asynchronous motors? Manufacturers generally offer three different motor protection circuit breakers, available for a wide range of voltages and currents, in order to meet most asynchronous motor protection needs. It is very common to complement motor protection circuit breakers with a contactor to allow automatic control of motor startup and disconnection. The system might also include and under-voltage protection device, which disconnects the motor in case the system voltage drops considerably below the rated value.

Motor Protection Circuit Breaker Sizing (Selection Guide)

The two main factors that determine the adequate motor protection circuit breaker size are the nameplate voltage and nameplate current, of the motor itself.

Motor Protection Circuit Breaker Specification Chart

MPCB manufacturers typically provide charts where the technical specifications of the circuit breaker are presented, in order to simplify the selection process. The following chart, provided as an example, is for the motor circuit breaker SGV2-ME model manufactured by CGSL. The current values at which the thermal and magnetic protections operate are displayed in the thermal release and magnetic release columns. Before installing a MPCB, it is very important to verify that voltage and current ratings are compatible with the motor being protected.

Conclusions of Motor Protection Circuit Breaker

Motor protection circuit breakers have a very important role in electrical safety, since the motors they protect have a wide variety of applications in commercial buildings and industry. Asynchronous motors, the most common type of electric motor in industrial and commercial settings, has special protection requirements that can only be met by a motor protection circuit breaker. It is also possible to complement MPCB with other protection or automation devices such as under-voltage protection, timers, and reduced voltage motor starters. Adequate selection of the MPCB is key in order to provide reliable motor protection. An undersized MPCB will not even allow the motor to start, while an oversized MPCB might be unable to detect over-current conditions for the electric motor being protected.

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