Motor control centers are modular systems, which fit in a cabinet; the entire control center contains the equipment necessary to power and control motors installed in production facilities. It is not necessary for all motor control feeder buckets to have their own separate power source as several can be powered by the same switch, which in turn gets its power from the utility company. In large installations, there will be a transformer between the incoming power from the utility company and the switchgear.
A typical motor control feeder bucket is a grey box which is large enough for a circuit breaker, motor starter, control transformer and relay. Feeder buckets are available in many different heights and widths to accommodate large components or additional components such as soft-starters or variable frequency motor drives.
The motor control feeder buckets are designed for easy removal. The entire device sits on a set of rails, which allow it to be easily snapped into place on the bus bars that are located on the back of the motor control center. The bucket comes complete with a terminal strip which allows easy and simple connection of field wiring. This solution allows the bucket to be pre-wired prior to installation in the motor control center.
Years ago, the motor control center included all the control that was needed for industrial motors, today; most installations use the motor control center to distribute power to individual panels. This solution reduces the equipment in the motor control center to nothing but a circuit breaker with an external handle to shut the breaker or open it. The actual motor controls are mounted in separate enclosures. This motor control feeder bucket arrangement is ideal as today’s modern programmable logic controls can be pre-wired and kept away from the main power enclosure.
The wiring setup:
The motor control center is the device which is wired to the incoming power supply. The first bucket is used to connect the incoming supply cables to the bus bars which are positioned in the back of the motor control center. The next bucket from the feed-in usually includes a circuit breaker panel which is used for lighting and power outlets; the next bucket will contain the transformer for the circuit breaker panel. This transformer provides low voltage power and is separate from transformers that supply control current to the array of buttons, lights and sensors attached to each motor.
There is a definite move afoot in industry to change from one centralized motor control center to a simple power distribution setup. A power distribution center is ideal for being the central point to shut off power to a large population of devices for maintenance purposes.
