The Technology of a Motor Control Center
All machineries that are driven by motors need to be controlled. The basic controlling operation of a motor is to switch it on or off, and this is usually done by a motor starter, which consists of an overload relay and a contactor. The motor is started when the contacts of the contactor are closed and stopped when the contacts are opened. This procedure is generally accomplished by start and stop pushbuttons. When an overload is experienced, then the overload relay disconnects the power to the motor. However, in an overload situation, the wires supplying power to the motor maybe short-circuited. To protect this, fuses or circuit breakers are used. To visually see whether current is flowing or not, indicator lights may be used. Thus, the motor starter is also linked with a circuit breaker or a fuse, pushbuttons, and indicator lights, which all together make a motor control unit. If there are many motors than an equal number of motor control units are required, as usually one motor is controlled by one motor starter unit. The motors are usually spread over a given geographical region and it is desirable to have all the motor control units at one central location, so that all the motors may be controlled from a single location only. When all the motor control units are physically grouped in one assembly and located at one physical location, then a Motor Control Center (MCC panel) is created. Definition The National Electrical Manufacturers Association (NEMA) in ICS-18-2001 defines a MCC as Combination Motor Control Units An industrial or a large commercial application needs effective power distribution, which is accomplished by switchboards, switchgears, panelboards, transformers, and MCC panel. These power distribution systems are used for several purposes like cooling, heating, driving motors, and lighting. Switchboards or panelboards mainly consist of fusible switches and circuit breakers; whereas MCCs mainly contain combination motor control units. However, many MCCs also contain other distribution devices like panelboards, and lighting transformers. The maximum voltage of a MCC cannot exceed 600 volts and generally, a three-phase supply voltage of 480VAC is implemented in a typical MCC. Bus Bars Each combination motor control unit is provided power by a bus bar, which serves to connect two or more circuits. The bus bars are vertical and horizontal metal bars that are connected together. Each vertical bus bar is connected with only one corresponding horizontal bus bar and remains unconnected with other horizontal bus bars. When the MCC is not in operation, the bus bars are at ambient temperature, which is the surrounding air temperature. When the MCC is in operation, then current flows thorough the bus bars and the temperature rises, but it is rises only to a certain allowed temperature. The ambient temperature and the allowed temperature give the maximum temperature to which the bus bar can rise. Standards for the temperatures are given by UL (Underwriters Laboratories) and NEMA. If the ambient temperature is 400 C, then the allowed temperature rise is 650 C (NEMA) and 500 C (UL), for a maximum temperature of 1050 C (NEMA) and 900 C (UL). Future The technology of a MCC is designed to provide safety, efficiency, and ease of use. With overall advancement in the academic field of Science & Technology, the use of robotics knowledge is also being experimented for controlling MCCs. However, as of now, this seems to be a far-fetched idea and better suited in the realm of science fiction. Nevertheless, advancement in the MCC expertise is underway, and the future of MCC technology looks bright. …if you want to read more about mcc panel