Motor protection is the isolation of the motor from the main supply when there is an abnormal condition in the running state of a motor(i.e. when the motor is supplied with electric power). A motor protection device is used to avoid the burning of the motor due to overload.

What is MPCB?

As the name implies, MCPBs are specially designed electrical protection devices to protect electrical motors(generally AC motors) from overload and short circuit conditions more effectively. It also protects the motor against phase unbalances, phase loss, line-to-ground fault, line-to-line fault, etc. MPCB has an inbuilt contactor and relay. So, there’s no need for external contactors and relays.


The main function of MPCB is to protect the motor from

  • Overload: It occurs when a motor draws current above its nameplate value for a long time. Overload is sensed by a bi-metal strip.
  • Single phasing or phase failure: Phase failure is detected by phase angle displacement.
  • Over/under voltage: Over/under voltage protection is generated by an electronic circuit.
  • Short circuit: Short circuit protection is given by solenoid.
  • Dry run (If motor used for water pump): Dry run is detected by lack of water pressure generated by the pump.

Working Principle of MPCB

MPCB is generally used as a Motor circuit breaker for low-rating motors. It can be considered a substitute for a Thermal overload relay with advanced features. The basic working principle of an MPCB is similar to all other Circuit Breakers.

  • Thermal Protection is used for Overload protection. Thermal Protection works with a bimetallic strip. It has these strips in all three phases which give overload protection. The bimetallic strip bends when the current passing through it increases from the rated current due to heat generated by the over current. The bending of the bimetallic strip operates the tripping mechanism of the Circuit breaker. It depends on the current setting of the relay.
  • For short circuit protection, it has an electromagnetic coil. A magnetic coil is shaped in the form of a small coil. If a high current flows through these coils i.e when the current rating increases, a force acts on the armature enclosed by the coil. This armature unlocks the loaded switch latch that releases the stored spring energy and hence opens the main contacts and disconnects the over current.

Selection Parameter of MPCB

The two major selection parameters for MPCB are as follows-

  1. MPCB voltage rating must be the same as that of the motor nameplate rating for which we are doing the protection.
  2. MPCB's current rating should be in the range of the nameplate's current rating.

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You can now buy motor protection circuit breakers(MPCB) along with other electrical appliances online at We offer you the top brand ABB products at the best and most affordable prices and with exciting discounts. We also offer the best quality products according to your needs and requirements.

Main Features of ABB MPCB

  • Annual control/short-circuit current and overload protection.
  • The adjustable current setting for overload protection and a magnetic trip indication.
  •   Disconnection function.
  • Temperature Compensation.
  •   Remote control via under-voltage release or shunt trip.
  • Short-circuit service breaking capacity Ics up to 100 kA.

Ranges of ABB MPCB Available at

●     MS116 with a standard performance range up to 32 A (0.10 A - 32 A).

●     MS132 /MO132  with high performance ranges up to 32 A (0.10 A - 32 A).

●     MS165 / MO165 with high performance ranges up to 80 A (16 A - 80 A).

●     MS132-T with high performance ranges for transformer protection up to 25 A (0.10 A - 25 A).

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