Enclosures - Preventing poor design degrading long-term reliability
Steve Gallon explains why the integrity of a systems design depends on the reliability
of conductors (wires, cables, and fibre optics), terminals, connectors, sockets, circuit boards, back plates, and the overall enclosure
Not wishing to teach Grandma how to suck eggs, it's worth reiterating electrical and electronic enclosures typically come in two grades: commercial and industrial.
Commercial cabinets ideally suit office and light industrial environments, whilst industrial equipment is normally more robust. The operating environment then determines the type of cooling, shielding, and IP protection needed.
These basic considerations establish the type of materials and plating or finishing needed for the enclosure to withstand the environment and successfully contain, protect and shield the device, to finally operate in.
Another consideration may be shock and vibration, especially in factories and environments prone to shaking as may found in the rail or mining industries.
Overall enclosure dimensions dictate the closest standard catalogue size available, and free space surrounding the cabinet works into calculations for selecting a cooling unit. (Heat exchanger and air-conditioner equations include the exposed surface area of the cabinet - enclosure bottoms and sides resting against walls and floors are ignored).
Intended use is important because some industries such as petroleum and food processing enforce rules and regulations concerning materials, finishes, paint, seals (for fluids and radiation), and explosion-hazard factors. For example, many food and beverage-processing plants mandate stainless-steel enclosures whilst other installations require GRP or polycarbonate enclosures.
There was once a time many UK panel builders and enclosure users overlooked GRP because they were of the belief that these products were not as strong as steel, however with today's advanced manufacturing techniques, modern GRP enclosures offer impact resistance (IK) ratings, equal to those of steel.
In addition and because of the material is inherently corrosion-proof, the suitability of GRP products for use in tough environments is amply demonstrated by their widespread adoption throughout Europe for extensive use in demanding applications which include traffic light controls, railway signalling, telecommunications and remote metering and monitoring.
Another issue crops up especially around telecommunications equipment, medical instruments, switchgear, machine tools, telephone links, and optical links. Many of these products are regulated by national standards, and special features may have to be incorporated in the cabinets.
Whenever possible, the designer should try to stick to standard enclosures as much as possible to keep costs down. What might be a custom job for one enclosure manufacturer may be a standard catalogue item for another. Standard enclosures, climate controllers, and accessories typically are available off the shelf or within two to three days. Modifications, however, may take four to six weeks!
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