Electronic and electrical equipment requires robust protection. A durable enclosure is vital to its safety so a designer will need to address several key considerations when building an effective enclosure.
When designing a complex network of electrical and electronic components, most of the time an enclosure is something of an afterthought. After all, it is simply a box that houses components, connections, wiring, controls units and other equipment – what a development engineer calls “the important stuff”.
Sadly, this is a misconception that leads to failure – especially if important design considerations are forgotten or unfulfilled. Although enclosures can seem like a non-critical element in system design, a failure to secure the equipment can result in a build-up of moisture or dirt, a drastic change in temperature and poor ventilation.
Keeping it cool
When designing a heat management system for an enclosure, manufacturers must account for external temperature fluctuations such as solar gain – heat from the sun. In addition, electrical and electronic equipment can generate significant heat inside the cabinet as a by-product of operation, known as losses. Failing to safely remove these losses will increase the temperature inside the enclosure and could adversely affect its contents.
One option is passive cooling, a method that uses convection to distribute heat from a higher to a lower temperature area. To do this, enclosures must be designed with strategically placed vents that replace the hot air inside with cooler, external air.
However, the feasibility of passive cooling depends on its environment, and the ambient temperature surrounding the enclosure must remain lower than the air inside it. Additional air filters may also be required to prevent dust or dirt from infiltrating the enclosure. Instead, design engineers may choose active cooling by installing heat exchangers or air conditioners to cool the air inside the enclosure.
Following the rules
For an enclosure to comply with local guidelines, manufacturers must consider its end destination. The International Electrotechnical Commission (IEC) 60529 Specification for ingress protection (IP) is for countries following this standard, whereas for the European market the applicable EN standard should be followed.
Understanding these regulations can be daunting, which is why manufacturers should work alongside their customers to advise on the most effective solution. If the IP rating is too high, for example, it will place tighter opening restrictions on the enclosure’s panel which restricts ventilation.
Enclosures should only be opened using a key or tool, and when all live parts are disconnected. Installing a viewing window reduces the need to access inside the enclosure. Other safety features include interlocking the enclosure door with a disconnecting device to prevent direct human contact with the equipment, should the door need be opened.
It’s a matter of materials
Of the numerous materials available for enclosure construction, each offers its own protective benefits. Whilst painted carbon steel is the most cost-effective metallic choice, it has limited resistance to solvents, alkalis and acids and is thus best suited to indoor applications.
Stainless steel provides a much higher resistance, and variants such as grade 316 are specified in industries that require resistance to chemical attack, such as pharmaceutical manufacturing, which must avoid excessive metallic contamination. As the material has better resistance against sulphates, seawater and high temperatures, we recommend this type of steel as the preferred choice for both indoor and outdoor applications.
Away from metals, fiberglass is a lighter weight choice, making it suitable for wall- or pole-mounted installations. As fiberglass is not conductive, any open circuit would stay safely inside the enclosure and current wouldn’t be transmitted through the material. The conductivity offered by a metallic enclosure enables it to be ground-connected to reduce the risk of electrical shock should an exposed conductor come into contact with the enclosure.
Ultimately, designers should never underestimate the value of enclosure materials. They may seem like just a box, but enclosures play a vital part in equipment protection and their design should be carefully considered.
Power resistor enclosures
Design engineers as well as resistor end-users across various industries need to understand the requirements of their power resistor enclosure, which provides a number of functions, including protection from harsh weather conditions, cooling, and preserving the safety of the public. Each of these specifications will vary, depending on the exact client requirements and the components they purchase; nevertheless, a full understanding is crucial to the design phase.
There are several key questions that must be answered to design and manufacture an effective enclosure that meets the required specifications. These will cover the final resistor environment, industry challenges, aesthetic considerations, health and safety, and choices around shipping and installation. By thinking about these points early, the final product can be designed to meet each and every requirement.
“We, at Cressall Resistors, produced an infographic to provide design engineers, as well as end users, with a checklist of things to consider when they are planning their resistor and corresponding enclosure,” said Andrew Keith, engineering director at Cressall Resistors. “Sometimes enclosures can be left as an afterthought, but this will rarely achieve the most efficient, advantageous solution. Thinking about the enclosure at the same time as designing the resistor is crucial to ensuring the final product will meet all the requirements, reducing the risk of compromises having to be made.”
By Andrew Keith, Product Development Director, Cressall Resistors