An electric enclosure is a cabinet for electronic or electric equipment for mounting displays, knobs and switches. It helps to prevent shocks to users of equipment as well as protect its contents from the vagaries of the environment.
The enclosure is only part of the equipment seen by users. It may be designed not only for its utility but also for its aesthetic value. The performance and features of the enclosures may be dictated by regulations, especially in hazardous applications like coal mines or petrochemical plants.
The enclosure may be subject to many demands in case of electronic packaging like radio frequency interference, heat dissipation, electrostatic discharge protection and also, functional, commercial and aesthetic constraints.
Electric outdoor enclosures are typically made of rigid plastics or metals such as aluminium, steel or stainless steel. The cabinets made of steel may be galvanized or painted. Mass-produced equipment will typically have a customized enclosure. However, standard models are created for small production runs of equipment.
Plastic enclosures are used for indoor applications and not for harsh environments. Where stronger materials are required, fibreglass, glass-reinforced and polycarbonate boxes are used, and they may feature a gasket to prevent seepage of moisture and dust.
Metal cabinets might meet the needs of conductivity for electrical safety bonding and shielding of enclosed equipment from interference from electromagnetic waves. Non-metallic enclosures may need extra steps of installation to ensure proper bonding of metallic conduit systems.
Electrical enclosures are installed in widely varying locations- often, a switchboard may be placed outdoors, vulnerable to high humidity, heavy rain, corrosive minerals like sea salt, solar radiation and dust. Another concern is that it is sadly becoming common prey for sabotage and vandalism. Hence, it is important to select the right enclosure material:
- Polycarbonate enclosures
This material has many advantages over metallic enclosures, especially its resistance to acidic and corrosive environments. It is surprising that such plastics often have great impact resistance and don’t scratch or dent easily. Its non-conductive nature gets rid of the requirement for earth bonding straps for covers and doors.
These enclosures are typically used for smaller applications like marshalling boxes and local control stations. They are rarely used in big sizes because of cost. Ideal applications include local control stations, small enclosures, chemical environments, and marshalling boxes.
- Mild steel enclosures
Steel has always been a commonly used material. This is because of its relatively lower price and high strength -some 25 times the strength of plastic.
But raw steel is highly vulnerable to corrosion. It must be coated using methods like zinc coating, painting, powder coating or galvanizing.
Mild steel enclosures are used for everything from indoor switchboards to roadside traffic control boxes. They are suitable for all outdoor enclosures except areas impacted by corrosion like coastal areas. Since steel is highly conductive, it is good to earth all steel surfaces to prevent electrocution. These enclosures can be used for almost all indoor and outdoor use, especially in non-corrosive and non-coastal areas.
- Aluminium enclosures
Just like steel, aluminium is also vulnerable to corrosion, but it quickly builds up a layer of whitish material called aluminium oxide which protects the inside layer of aluminium from Oxygen and prevents further corrosion. Uncoated aluminium can be used easily for outdoor applications but are painted, and powder coated for aesthetic reasons.
Aluminium is lightweight but not as strong as steel, so thicker sheets are used. One benefit of aluminium is that it is not magnetic, avoiding the formation of eddy currents inside the enclosure. Such enclosures are ideal for coastal applications.
It is a steel alloy which contains a quantum of nickel and chromium that makes it virtually impervious to staining and corrosion. There are several grades of stainless steel. Most common are 304 grade (made of 8% nickel and 18% chromium) and 316 (made of 2% molybdenum, 10% nickel and 16% chromium).
This steel alloy is harder than mild steel. It is tougher to cut and work with but is stronger structurally. Because of the high resistance to corrosion, it is commonly used in a totally uncoated form, even in locations, outside. Uncoated stainless steel is typically polished for aesthetic reasons. This steel is popular in the food industry as it can be washed easily, getting rid of bacteria and grime.
However, because of its content of other metals, stainless steel is 3 times as expensive as mild steel. The high nickel content makes higher grades of stainless steel more expensive. Ideal applications are for electrical enclosures in outdoors, even in coastal areas and other corrosive environments.
Enclosures for certain uses have partially punched openings (knockouts) that can be removed to accommodate conduits, connectors, and cables. Where these are small and mainly intended to conceal electric junctions from sight or protect them from sabotage or tampering, they are also called as junction boxes, street cabinets or technically as serving area interface.
These are some of the top facts about electric enclosures.