Motor Control Centres are used in general to describe combinations of enclosures, busbars, circuit breakers, power contactors, power fuses, protective relays, controls and indicating devices.
Motor control centers (MCC) are centralized systems that organize the controls for industrial electric motors typically associated with factory machinery. These centers range in size from smaller moveable cabinets to larger systems that are bolted to the floor.
Motor controls can vary in range from motor starters or contactors to more complex systems, including variable frequency drives that allow the motor speed to be adjusted. Most motor control centers also contain some form of motor protection, often in the form of circuit breakers, overload relays or other devices that protect the motors. A thermal overload relay will protect a motor from overheating but will not protect against a short circuit where a circuit breaker or fuse will. often both are used.
why do we use them?
If we have large industrial area where many electrical motors are used.
these motors need to be protected from abnormal conditions and/or any overload. But controlling and monitoring the operation of each motor from the field requires hundreds of controllers and control panels.
However monitor and control is always done from the electrical central room, therefore an Motor control center is located in that room and electrical signals are sent to the motors in fields.
Components used in MCCs
There are many common components among all types of MCCs and some special components that depends on the application.
- We have already discussed usage of those devices in other articles, but briefly they are used for protection from faults. The used circuit breakers types shall be as follows:
- Circuit breakers feeding loads 1-7.5kW shall be of the Manual Motor Starter or Motor Circuit Breaker type.
- Circuit breakers feeding loads up to 0.75kW shall be of the miniature type.
- CB feeding loads greater than 7.5kW shall be of the Moulded case type.
- Indicator lamps: They are used to show the status of operation whether it is start, stop or fault.
- Push Buttons and Selector Switches: They are used for start stop operation of the motor either manual or automatic.
- Digital Multi-meter: To measure voltage, current and frequency.