INDUSTRIAL ENCLOSURES often are viewed as necessary evils that present more of a challenge than they should. There rarely is anything glamorous about them, and if they do everything they should for your customer, youll never hear about them again. If your enclosure fails to do something its supposed to, youll never hear the end of it.
The task of the industrial enclosure seems simple, yet when presented with all of the constraints that it needs to work within, it can get very complex.
The job of the industrial enclosure is to protect control components from the rigors of the environment, including exposure to dirt, chemicals, moisture, heat and physical harm. Further, it should provide protection for all personnel working in the vicinity of equipment under control (EUC) from electric shock.
This sounds simple enough, except when you add constraints such as footprint, thermal loading, and other dimensional aspects. After you have figured all this out, which may take a bit of doing, you then need to ensure that it fits within the ever-shrinking budget that youve been allotted.
Advances in the area of industrial enclosures over the past several years have been impressive and make the job of specifying them easier, but many of the tried-and-true principles still apply (See Figure 1 below).
Machines today are more and more modular. The base machine is designed, then options are added to and subtracted from this base design as directed by the customer. With modular machine design, a modular enclosure design makes sense as well. Enclosure systems that can be scaled to meet specific needs save me a lot of time, states Keith Beadle, controls engineer for Valeo Electrical Systems (www.valeo.com), Rochester, N.Y., a systems supplier to the automotive industry. By using a flexible enclosure, it allows me to maximize the amount of engineering that I get to re-use from one project to the next.
Figure 1: Get the Most From the Box
The components in this enclosure might be densely populated, but application of proper design principles makes it a workable and visually agreeable panel.
Because of the frame, modular enclosures can grow quite large by baying the enclosures together. Just bolt a couple of frames together for one contiguous mounting panel. Further, the hole patterns in the enclosure frame lend themselves to mounting devices just about anywhere.
Beadle recalls equipping modular enclosures with mounting bars that allowed him to affix devices on sidewalls, doors and floors. He says hes even seen them mounted to ceilings. Accessories are also available that allow the user to make use of nearly every piece of real estate available inside of the box.
Wont Fit? Customize It
Despite the enhancements added to the modular enclosures, sometimes all your devices still wont fit into the space allotted. The mechanical design of the EUC, footprint constraints, or custom control hardware requirements might still dictate something different, including varying degrees of depth within the enclosures rectangular geometry (See Figure 3 below). When we create a control system, some of our enclosures are standard catalog items, and some are heavily customized from the factory, says Robert Spencer, applications engineer from Electric Service and Sales Inc. (www.esscoinc.com), a system integrator out of Greensboro, N.C., with its own UL508A panel shop.
Product costs and labor costs are a balancing act for us. We have found that the deciding factor [whether to customize enclosures ourselves or have them made] is volume and quantity discounts. For our OEM accounts that use a high volume of identical enclosures, the manufacturer modifications are the way to go. But for smaller quantities, we can do it cheaper and faster in our shop.
In addition to custom modifications from his enclosure vendors, adds Spencer, he gets detailed CAD drawings of the enclosures. Saginaw Controls (SCE, www.saginawcontrol.com), says it understands the need machine designers have for CAD drawings and the convenient customization of enclosures. Our customers can download a standard drawing from our web site, add modifications to the drawing and send it back to SCE, explains Dave Pankow, national sales manager for SCE. Our Customized Standard Enclosures Program provides the cost effectiveness of using standard enclosures, while providing the cost savings of having these modifications done before the enclosure arrives at your facility.
To meet the customization needs of its customers Rockwell Automation took a different approach. The ability to configure the enclosures to meet the customers design without much added cost was seen as a real problem, says Lynn Chin, product manager for Rockwell Automation (www.ra.rockell.com).
Using our Mod Center Plus on-line configuration page, a customer can specify a completed assembly to fit certain applications. This customization includes not only the electrical enclosure, but one that is fully outfitted with the internal hardware required for the job. The designer avoids the need for panel layout design or bill of material. Best of all, you know that when the assembly arrives at your facility, it meets all applicable UL and NEC codes for your application with no need for you to look them up.
Still Not Right? Lose the Box
Of course, there are alternatives to the industrial enclosure. Some new product developments allow designers to move much of the content out of the box and on to the machine itself.
Rockwell Automations On-Machine line of products includes IP67-rated distributed I/O devices along with a variety of other products. The system lets designers place automation devices closer to points of control on a machine, rather than housing them in a central control enclosure.
|Figure 2: Framed for Strength|
|Modular enclosure designs typically acquire their strength from a frame construction within the enclosure. A variety of accessory mounting hole patterns can be designed in.|
If You Cant Stand the Heat
One of the ironies with industrial enclosures is that you work hard to get everything enclosed to protect it, and then find yourself stuck with the problem of it being closed up too tightly. Most controls systems today need some form of cooling in order to insure reliable operation.
The most difficult challenge we face has to do with temperature control, says Spencer. This arises from a combination of factors--the necessity for a sealed enclosure is only part of it. Many control systems today employ either variable-frequency or servo drives, which generate a lot of heat. This heat, when not dissipated, can lead to premature failure of the electronics of the control system that runs these drives.
According to Herzog, an increase in the operating temperature of 10° C over the maximum rated temperature shortens the service life of semiconductors by half. Because of this, it is very important that an operating temperature within the manufacturers specifications of every device in the enclosure be maintained.
How to go about achieving this balance, however, can be difficult to determine. Factors that affect the thermal performance of an enclosure and, as a result, the amount of cooling required include the heat dissipated within the enclosure, maximum ambient temperature, the cabinets material, mounting location (free air or against a wall or other device), and air quality (dust or other particulates in the atmosphere).
This can create problems as well. We have been purchasing NEMA-12 enclosures but when they are installed at the plants we discover the contractors drill holes and don't seal them. Consequently the ventilation system is not properly handled and the NEMA features are lost, states Alejandro Barreto, controls engineer at Carmeuse North America Inc. (www.carmeusena.com), a Pittsburgh-based lime products manufacturer. Each time an opening is installed for either climate control or cable entry/exit, the new opening must be sealed to the rating that is desired or the NEMA rating for the entire enclosure is compromised. According to Rittals Herzog, an air leakage rate of just 3 CFM can lead to a continuous vapor condensation rate of 5.5 tablespoons per hour.
The cost of fiberglass and thermoplastics has risen over the last year, but not as much as the price of steel. As the cost delta between alternative materials and steel closes, the advantages of using alternative materials might be realized more easily. Typically thought of only for washdown areas or where harsh chemicals are used, alternative-material enclosures are starting to appear in a diverse set of non-traditional applications.
One advantage of composite materials is that they are easily modified for wire and cable entry/exit points. Even if you pay slightly more for the box itself, the labor saved in preparing the box for duty could more than cover the difference. Additionally, these non-metallic enclosures are lightweight and durable, making them even more attractive.
Figure 3: Play All the Angles
The mechanical design of the control components, footprint constraints, etc., might dictate something different in enclosure shape, including varying degrees of depth within the rectangular height and width.
According to Spencer, he believes electrical enclosures are his companys showcase opportunity. Just as the exterior of an automobile is the component by which the entire car is judged, our enclosures are what we as a company are judged by.
While its true that the outside of the box needs to look professional, the interior must present a clean, polished look as well. This can present a challenge considering the higher component density that manufacturers are able to achieve.
Features designed to help with the space usage and mounting of control devices are all very important, but it doesnt address all the needs machine and/or panel builders might have with an industrial enclosure. Wire management can be a big issue as well, and getting all of the necessary wiring into and out of an electrical cabinet often is no small feat.
To facilitate the maneuvering/positioning of cables to the appropriate entry/exit point, manufacturers can supply options that help direct and guide these power, control and networking links. Connector covers, removable gland panels, and cable-collecting rails are all standard options that we provide to help keep the interior neat as well says Herzog. Another innovation that made its débute at the Hanover Fair is an Ethernet connection block. With the rapid growth of Ethernet, this allows our customers to neatly organize and collect their Ethernet communications cables into one area with easy access.
False bottoms, often referred to as cable chambers, and cable closets located on the side of electrical enclosure, also are alternatives that afford the ability to direct cables safely out of the enclosure, especially as the volume of conductors increases. The method protects conductors from harm, and presents a clean look since the mass of cables and wires can be hidden away Herzog explains.
Enclose the NoiseElectromagnetic interference, or noise as it is commonly known, is another wire and cable-related issue that many manufacturers are taking steps to help with. Innovations such as zinc-coated mounting panels, EMC-friendly strain reliefs, and integrated grounding systems all help machine builders avoid noise issues from the beginning of the design, often without even realizing it. Addressing some of these issues up front may save a lot of time trying to track down the source of noise related nuisance faults later on--especially those intermittent ones that keep your machine from meeting run-off criteria.