Getting into Enclosures

Housing for control and automation devices and networks is evolving right along with the devices they contain, so it's even more important now to choose the appropriate enclosure for your application. Here's how.

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Simpler Specifying
To help users select the most appropriate enclosures, Orvik adds that Hoffman offers six tips to help them cover and evaluate all of the necessary options:

1) Application. By fully understanding the demands of your application, you can rank its most important features and attributes. For instance, do you need a high level of protection against corrosion? Is your enclosure in the traffic areas on a busy plant floor or in a less conspicuous location? Do environmental contaminants such as dust or oil pose a threat to your equipment? Answering these concerns will help narrow selection options regarding enclosure type, materials and performance. Ranking these considerations allows you to better recognize priorities needed for your application. Use these requirements to select from welded steel or the corrosion protection of stainless steel. Perhaps an aluminum, fiberglass or ABS enclosure better serves the application, and provides the proper level of protection, strength, performance and value.

2) Size. Early in the process, you'll need to determine the physical characteristics of your enclosure. Consider the dimensions of the equipment you'll be housing to calculate the total amount of panel space you need, including minimum height, width and depth. Many control and network devices require 19-in. and 23-in. rack standards, which may enable you to select a modular enclosure design, while other types of electronics may require a different size to accommodate your equipment.

After you determine the containment size of the enclosure, you'll also need to consider if any space or use limitations exist in the installation environment. There are often many different cabinet and mounting configurations that can provide the performance you require. An experienced application engineer or knowledgeable distributor can present options that will fit most effectively within your workspace. These might include horizontal, low-profile, or wall-mount cabinets or even portable enclosures.

3) User Interface. It's seldom adequate to specify a simple square box. Examine your need to access the enclosed equipment. Will accessories make the enclosure user-friendly? What is the anticipated frequency of service or maintenance? Are there cleaning, ergonomic, security, safety and usage considerations? Considering these requirements, you might select removable panels, wiring and/or backplane access. This can be through an added set of doors, locking latches, reconfigurable interior mounting, secure cabinets with partial accessibility to keyboards or a limited number of components. You also can address usage issues with operator interface workstations or pushbutton enclosures. You’ll also need to assess the routing of wiring, and consider the mounting option that will work best for your application.

With every enclosure there are two environments that require attention: the interior environment of the populated enclosure and the exterior environment surrounding the enclosure. Each presents distinct challenges to proper specification. NEMA standards can help you evaluate your needs where non-hazardous environmental conditions exist, and other worldwide standards can help you narrow your specifications as well.

4) Environment. Examine the immediate area in which you intend to install the enclosure. Will your enclosure be installed indoors or outside? Assess the environmental threats to your components. Contaminants may range from dust, water, oil and dirt, harsh chemicals, UV light, solar heat gain, weather forces, salt water or temperature extremes. In an equipment-rich environment, hidden threats might include electromagnetic or radio-frequency interference, which can play havoc with enclosed equipment. In a busy industrial area, the enclosure could be subject to periodic accidental impact or shock. And more sensitive, critical components could be at risk from excessive vibration or seismic dangers in certain geographic regions. Suppliers offering a complete line of enclosures and in-house testing can address your performance needs in even the most demanding environments.

5) Additional Protection. Whether generated internally or externally, excessive heat and humidity are the most common challenges in protecting components from premature failure or unreliable performance. Todays compact devices consume more power and generate more heat in less space, making thermal management an even more crucial consideration when specifying an enclosure. Because managing excessive internal temperatures is so critical to reliable operation, most manufacturers offer solutions to deal with these conditions. For example, Hoffman provides free thermal management sizing and selection software to help you calculate your heat dissipation needs based on your specific equipment, and suggests the appropriate thermal solution for your enclosure.

6) Certifications. Ratings governed by national and international standards organizations such as NEMA, UL, CSA, IEC and VDE are critical to help you specify the appropriate product for your application. These ratings standardize product performance from one manufacturer to the next, identify an enclosure's ability to withstand environmental influences, and/or offer assurance that products conform to established guidelines for performance and public safety. Standards such as UL and CSA require enclosure testing by qualified evaluators and perform site inspections to assure manufacturing compliance for methods and materials. By selecting a manufacturer that demonstrates strict adherence and fluency with international standards, your enclosure will not only perform in a safe and effective manner within your application, but will also satisfy electrical/building codes, OSHA requirements and even workers' union-based provisions.

In addition, RoHS, which regulates environmentally sound end-of-life disposal of components, continues to receive attention. This EU directive went into affect in July 2006. China and California are expected to follow with their own versions.

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