The electric and electronic components which are necessary for the control of a plant or a machine are located in a control cabinet. The closed control cabinets protect the components against contamination and moisture, thus components with the lowest protection type can be used (IP protection classes according to DIN EN 60529). Inside of the control cabinet the ideal temperature for electric and electronic components can be uphold by the use of air-conditioning or of control cabinet heating.
Generally control cabinets can be subdivided into control area and power range. The power range is composed of components and the wiring for voltages with 230V or more e.g. the activation of electric motors with contactor triggering, soft start or frequency converter.
The control area consists of components and voltages for low voltages, e.g. a programmable logic controller, briefly PLC. The signals of sensors from outside the control cabinets are wired on terminals and thus added to the PLC.
Terminal boxes with terminal blocks can be applied in the same way locally to the plant as electronic components belonging to the control. The connection to the control cabinet takes place by the use of cords or different bus systems. As a result the effort of the wiring is reduced.