What Is A Motor Protection Circuit Breaker?
Post By: Ryan King On: 10-09-2018 Read Time: 3 minutes - Guides
Post By: Ryan King On: 10-09-2018 Read Time: 3 minutes - Guides
A Motor Protection Circuit Breaker is a simple electromechanical device that protects an individual electric motor against overload, fluctuations in input current or unscheduled interruptions to the main circuit. This includes line faults and phase loss or imbalance in three phase motors. A Motor Protection Circuit Breaker saves on space and costs, providing fuseless protection that switches motors off instantly to prevent damage. It will also safely disconnect the current in the event of a short circuit. It will usually be equipped with a thermal delay to allow the motor to cool down, and sometimes with automatic reconnection when it has done so.
The MPCB is constructed with three main functions, specially designed for the protection of electric motors.
A manual interrupt mechanism is also incorporated in the MPCB, which allows electric motors to be disconnected manually for standard maintenance or replacement.
There are two main reasons that excess current occurs; overloads, and short circuits. Overloads can occur when electrical equipment draws only slightly more current than it is rated for, but this can build up over time. Overloads do not cause damage when they first occur, but only when left unchecked. Conversely, short circuits occur very rapidly, and can produce currents that are far in excess of a full rated load. For this reason, short circuits must be dealt with immediately.
Differentiating between a Motor Circuit Protector and a Motor Protection Circuit Breaker is really splitting hairs, since an MCP is effectively just a special type of circuit breaker that only protects against short circuits. In order to protect against overloads when using an MCP it is necessary also to install an overload relay. These are common in industrial Motor Control Centre assemblies, where space is not such an issue and multiple components are collected together. MCPs are also only generally used in branch circuits, while MPCBs are more commonly used in feeder circuit,
MPCBs are preferred for low voltage switchgear, because they combine both types of protection in one thermal-magnetic circuit breaker, and don't require additional relays. They also cut down on reset time after a short circuit or overload, reducing overall operational downtime. Motor Protection Circuit Breakers come in a wide variety of sizes and settings which allows maximum flexibility in installation. A lot of low voltage control gear is now also constructed in modules, so that a number of MPCBs can be integrated into a compact unit with other devices.