switch cabinet
A control cabinet houses the electrical and electronic components of a process engineering system, a machine tool or manufacturing facility that are not located directly in the machine ( field device ).
Construction and manufacturing
In the simplest case, it only contains terminals in the form of terminal strips for the clear electrical connection of various components of a system ( terminal box , distribution box ). In a closed cabinet, accidental and unintentional contact with live components is impossible; Cabinets that contain touchable parts with dangerous voltages inside can only be opened with tools (switch cabinet key, triangular or square key).
Manufacture of common sizes is carried out by the switch cabinet manufacturer or, in the case of special designs, by the machine manufacturer himself. The internal assembly takes place in an electrical workshop. The finished control cabinet can have plug connections (electricity, media) so that it can be delivered as a transport unit.
function
An empty housing should provide the following functions for electrical and electronic equipment :
- for the components in the interior:
- Protection against dust and water ( degree of protection , IP protection classes according to DIN EN 60529)
- Mounting and structuring of the internal structure (e.g. support rails, mounting plate, division into power and control areas)
- Protection against overheating ( control cabinet air conditioning )
- Protection against electromagnetic interference ( EMC )
- Protection against mechanical influences, vandalism and earthquakes (cabinets with additional struts)
- for the environment:
- Shielding against electromagnetic emissions
- Protection against contact with dangerous voltages ( protection classes : protective earthing or protective insulation )
- Fire protection (special solutions for smoke extraction systems)
Some control cabinets have a window for reading / recognizing switching states or measured values.
Many control cabinets have an emergency stop button on the outside and / or a suitable main switch for shutting down the associated machine in the event of danger, which can be locked for the machine service.
Types
As a rule, switch cabinets are made of painted or powder-coated sheet steel. Depending on the application - (e.g. when installing outdoors), the switch cabinet housings are also made from sheet steel with a special outdoor coating or from aluminum, stainless steel sheet or plastic.
The standard color for painted control cabinets is currently RAL 7035 (light gray), after RAL 7032 (pebble gray) was previously used. For switch cabinet manufacturers who have specialized in the construction of special switch cabinets, the switch cabinet housings can also be coated / painted in special RAL tones.
For corrosive environmental conditions as well as pharmaceutical and food companies, cabinets are also made of stainless steel, which are usually not painted.
The following designs are common:
- Floor-standing control cabinet: Stand-alone housing with one or two doors, often with castors
- Baying control cabinet: Individual elements without side walls, cables and lines can be laid internally over the elements. Walls can be attached to the ends of the screwed- together panels . In modern modular switchgear cabinets, the front posts can be removed to lay cables.
- Terminal box (any installation)
- Wall housing (wall mounting)
- with inner swivel frame so that additional mounting surfaces are available for better space utilization
Control cabinets can also be supplied with additional components that are already pre-assembled or included:
- Fans , filter fans , cooling air openings (slots, grilles or separate roof)
- Heat exchanger
- Cooling units (enable cooling with a tight housing)
- Interior lighting
- Feet or castors
- Cable entries
Further options are e.g. B. Locks and transparent doors.
Special control cabinets
In the case of technically complex control cabinet requirements, some manufacturers can adapt the housings to customer requirements in advance. There are hardly any limits to the shape, size, color, function, etc. of the control cabinet for individual control cabinet production. Depending on the requirements, housings are already manufactured with gills, holes, cut-outs, control cabinet viewing windows and much more.
Dimensions / control cabinet sizes
The following sizes are standard sizes for free-standing or modular cabinets, which are combined accordingly:
- Width: 600, 800, 1000, 1200 mm
- Height: 1600, 1800, 2000, 2200 mm
- Depth: 400, 500, 600, 800 mm
Compact control cabinets or wall housings are usually available in the following standard sizes, depending on the control cabinet manufacturer:
- Width: 200–1200 mm
- Height: 200-1400 mm
- Depth: 125-400 mm
Terminal boxes or switch boxes / switch boxes are available in these standard sizes, depending on the manufacturer:
- Width: 150–400 mm
- Height: 150-400 mm
- Depth: 80-120 mm
Control cabinets with a width of around 600 mm on the inside often have threaded straps on the side or brackets for inserting cage nuts for inserting 19-inch racks or subracks . Such control cabinets are also called racks .
literature
- Theodor Schmelcher: Handbook of Low Voltage, project planning information for switchgear, switchgear and distribution boards. 1st edition, Siemens Aktiengesellschaft (Abt. Verlag), Berlin and Munich, 1982, ISBN 3-8009-1358-5
- Ernst Hörnemann, Heinrich Hübscher: Electrical engineering specialist training in industrial electronics. 1st edition. Westermann Schulbuchverlag GmbH, Braunschweig, 1998, ISBN 3-14-221730-4
