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Dress control equipment appropriately for the environment

Oct. 28, 2018
Control-enclosure selection is important in the factory to meet the environmental needs of the application

The mechanical engineer asks the controls engineer, "How big of a control enclosure is needed?" If the controls engineer has not spent any time creating a design, the answer given, if any, is often just an educated guess. Instead, there should be many questions.

However, the obvious answer is the enclosure must be suitably sized for the application needs, but that will take some design work for an accurate answer. And does anyone know where they want to mount it? Also, don't forget, the enclosure needs to look good while environmentally protecting the control components inside, unless you are OK with an ugly design.

Before control-panel sizing and selection begins, the control-panel design should have already started. There are some basic design decisions that need to be made to get the preliminary squares and rectangles on paper, consuming panel space. The major components planned in the control enclosure should be listed in a spreadsheet, and a basic sketch of the electrical schematic, including the panel layout, should already exist.

When it comes to the panel layout, review previous or standard designs and related panel layouts, if available. Sometimes, an estimate is acceptable and using previous designs and then noting the new machine's complexity based on the major components listed and the documented number of expected I/O points will get a designer in the ballpark on size.

If no previous design exists or more than an estimate is needed, the control-system design must be well on its way or complete. The design will detail the type of controller and the number of motor starters, drives, power supplies, fuses, circuit breakers, terminals and such devices needed. These devices populate what must be a scaled control-panel layout created using a CAD program. When it comes to enclosure sizing, nothing beats a completed design that includes 20% or more spare panel space.

The mounting location of the enclosure also has a big impact on enclosure selection. Enclosures are often bolted directly to custom machines and OEM equipment, but will it mount under, to the side or take up the whole back of the machine? It depends on both the mechanical and electrical designs. You guys should talk.

Other applications will require the enclosure be separate from the machine in freestanding or wall-mounting configurations. This drives the type of enclosure and accessories.

The enclosure could be freestanding, or feet may need to be added to make it so. Other installations may require mounting tabs on the enclosure for wall mount. These tabs can be welded on by the factory or as a bolt-on accessory that attaches to holes in the rear of the enclosure.

Despite an enclosures size or mounting location, the control enclosure must look good.

After my tour of the USS Midway aircraft carrier at the USS Midway Museum, a maritime museum located in San Diego, alongside Navy Pier, I now know where the battleship-gray control enclosure was born. The U.S. Navy had much to do with it, and it started in the early 20th century.

There is nothing wrong with using battleship-gray enclosures. Just like bell-bottom jeans, bouffant hairstyles and the hula hoop, they have all, somewhat gracefully, stood the test of time.

It is important to get the enclosure specified and sized early in the design process. This will help to ensure time in the schedule to order a customized enclosure. Of course, you could just pick an off-the-shelf gray enclosure and cut the holes yourself, but that is a lot of work. Customized enclosures can be ordered from a manufacturer and can include nonstandard physical dimensions, cutouts, special features, such as swing-out panels and racks, and exterior paint colors.

Some people will wear Bermuda shorts and deck shoes, with no socks, to the farm, but it is better to be properly prepared to not stick out as the city guy who didn't know any better or didn't care. It's better to wear jeans and boots and bring the bug spray and sunscreen. Similarly, the control equipment must be dressed properly, and it depends on the destination, as well.

Finally, this brings up NEMA and IP ratings. Where is the enclosure going? Some may go in an office, clean room or semiconductor facility, which may limit the enclosure's duty to only protecting personnel from electrical shock and the components from mechanical damage.

However, in manufacturing facilities, such as automotive and metal cutting, the factory floor has many environmental risks for control components. Water, oil drips, spray and high-pressure washdown are just some of the means to damage components. Locating these components on the farm or outside under cover or in direct sunlight just adds to the risks.

The NEMA and IP ratings were certainly born because of the environmental risks. What happens outside a control enclosure can and will affect what's in it. It is the enclosure's job to provide protection from contamination and corrosion. Electrical specifications demand it. While the seal on the enclosure door and conduit fittings must protect from environmental issues, the enclosure material and paint finish must be up to the task, as well. And you may need a jacket.

The control components need to be dressed properly. Get with your favorite enclosure vendors, but be sure to have the enclosure size, mounting configuration, color and environmental requirements available to help you to specify the proper control enclosure.

ALSO READ: Control panel design starts with the basics

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About the Author

Dave Perkon | Technical Editor

Dave Perkon is contributing editor for Control Design. He has engineered and managed automation projects for Fortune 500 companies in the medical, automotive, semiconductor, defense and solar industries.

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