Fashion and function

Michael Murphy
Rittal Corp.
Springfield, Ohio

A unibody welded enclosure limits designers to a narrow selection of configurations and flexibility.

The process of selecting floormount or freestanding enclosures for electrical systems involves plenty of variables, not all of which are obvious. Of course, enclosure size and providing enough space is essential, but there are other questions to consider when designing a control system, such as what is the application. Design requirements may be defined by application needs, be it industry type, equipment type, or installation type. Also, consider the environment the enclosure will be in, whether it be outdoors, indoors, or a harsh environment. In addition to the space requirements inside, take a look at space restrictions that might limit enclosure size — outside the enclosure. Temperature conditions outside and inside the enclosure are another factor.

Other considerations when selecting an enclosure include whether or not the user interfaces with the enclosure; any ergonomic considerations; the material of construction; any aesthetic issues; how panel builders and field installation personnel are going to work with and enter the enclosure with cables, conduit, or raceway; service issues; and internal design requirements for the enclosure.

Traditionally, the answer was a unibody welded enclosure. When selecting a unibody enclosure, the primary concerns are:

• How big does it have to be and what mounting panel size is necessary?
• Does it come in a standard model from the catalog? If not, a special size and configuration must be ordered.
• Are any value-added services necessary, such as special brackets, holes, paint, locking handles, and/or a floormounting kit?
• What material is needed?
• What NEMA rating is required?

Although this is a simplified list, it includes the primary drivers when it comes to selecting a unibody enclosure. Going outside the parameters of a standard catalog solution leads to quality, lead-time, and potential workmanship issues. Not to mention, there are additional engineering and procurement costs due to the need for special configurations, considered nonstandard.

A modular enclosure is just another way of protecting electrical components from an unsafe environment and keeping personnel from harm.

The design concept is simple. A welded frame provides the overall strength and form of the enclosure. The enclosure builds up from the frame with the addition of doors, sidewalls, roof, base, rear wall, and mounting panels. These enclosures meet certifications such as UL Type, NEMA, and IP.

A multiapplication approach to modular design means all modular enclosures use the same fundamental platform. This consists of a frame structure, configured with surfaces (skins) to complete the design. The overall strength of the enclosure comes from the frame. This approach provides near endless configurability and, therefore, enough flexibility for any market. One application example is an electrical drive housing. Start with a frame that suits space requirements, then add solid doors, roof, mounting panel, and a rear wall. In this case, most likely, multiple doors and frames will be necessary to accommodate the drive line-up. The size of the line-up dictates the number of doors and frames required. Designers may need to gang enclosures together to accommodate the overall system.

Flange-mount enclosure, sidewalls, and a hardware interlock kit complete the design. A base is an option as required. As the system grows, it's possible to expand the enclosure without going into a new, larger unibody multidoor unit. Bays can be added to an existing system as required. Modular enclosures also provide significant advantages in the field. Additional bays easily accommodate field expansions and retrofits.

THE ENVIRONMENT
The most common installation in the industrial market is a NEMA-12 carbon-steel enclosure. This is also the easiest place to use a modular enclosure. Modular enclosures can serve in NEMA-4 and 4X applications as well and there are many solutions available. But the prevalent application is NEMA-12.

Modular enclosures can be bayed together without redesigning an entire enclosure system.

Space restriction is one of the biggest concerns impacting enclosure design. Typical limiting factors include floor space in the control room; whether the enclosure can mount directly to the floor or if it needs bottom clearance; height limitations; and aisle or safety egress to name a few.

There are many options including full-size mounting panels; swing-out mounting panels; swing-out 19-in. frames; partial mounting panels; mounting panels and doors front and rear; and components such as bars, chassis, and rails.

All these accessories can be designed into the modular enclosure from standard catalog items. The same could not be said of a unibody enclosure without special designs. Typically a modular enclosure will have 30% more mounting panel space than a unibody enclosure of the same size.

Frequently temperatures inside and outside the enclosure can play a large part in determining the design. High ambient temperature combined with high internal heat generation can require additional, active cooling such as an air conditioner or heat exchanger. If so, the space needed to mount these devices becomes an issue. There are only a few ways to cool an enclosure below ambient. Assuming there's room for active cooling, options may consist of one or a combination of the following: an air conditioner or air/water heat exchanger; recirculation fans mounted to plates to move the air around more efficiently; air plenum with directed air at hot spots from plant-supplied ducting; fans and filters on the door; and an integrated door/AC combination that only modular offers.

ERGONOMICS
In many applications, the freestanding control enclosure doubles as an operator interface point. Traditionally this was accomplished by installing pushbuttons or similar discrete devices in the door, along with data-entry portals such as a keyboard or touch pad.

It can be difficult to make operator controls ergonomically friendly, aesthetically pleasing, and easy to use on unibody enclosures. In contrast, a modular platform offers a plethora of solutions and configurations. For example, partial doors and panels allow compartmentalization of the front of an enclosure, separating the control, viewing, and keyboard areas. Other configurations include keyboard drawers with integral mouse pads; sloped viewing windows and shelves; and writing surfaces. Also, modular enclosures can bay another module directly onto an existing control enclosure and create an entirely independent HMI solution, integrated into the current design.

AESTHETICS
As with unibody, there is the choice of painted carbon steel and stainless steel for modular construction. The selection process is the same, via part number differentiation. Remember, however, that the surfaces are removable from the enclosure, giving further flexibility. Materials can be mixed and matched as when the need arises for wipe-down surfaces.

In today's market, especially in the OEM sector, aesthetics play a larger role. Of course, functionality, precision, quality, delivery, service, and price are still the largest factors for OEM equipment. Aesthetics, however, is becoming the finishing touch and the enclosure is part of that. Designers are being challenged to make their product look better and still be cost competitive. Many marketing departments are dictating the final look of the product to assure it appeals visually to the customer. In general, modular enclosures present a cleaner and more technologically advanced appearance, albeit with the same control solution inside.

The practicalities of field installation impact not only the size, but also the arrangement of devices within the enclosure. It also affects space requirements in the surrounding area as well as mounting possibilities.

Installation of unibody enclosures is straightforward but also limiting. With modular, removable surfaces simplify assembly and construction significantly. Also, any panel that needs modification is removable. The work takes place in the flat, improving speed and quality simultaneously. Finally, consider a mistake or scratch on the enclosure. With a unibody, the hole must be plugged, a cover plate made, sanded, and refinished. Alternatively, the enclosure becomes scrap. With modular, the damaged section-is discarded and a new one added.

IN THE FIELD
Depending upon where the entry point is, the openings can be precut or left to field installers. Ultimately, it's best to plan on installers cutting into the enclosure. Also, the internal design must avoid any interference points. Field installation concerns typically include, but are not limited to:

• When the installer cuts into the panel, will metal filings fall on the electrical equipment?
• How will the equipment be protected during installation?
• Is there enough room inside the enclosure for wire bending (per NEC), wire bundles, termination points, tie-off points, and spares?
• Is there enough room around the enclosure for the installer to work?

HOW IMPORTANT IS SERVICE?
Service is incredibly important and differs for every job. Where price and delivery is important, the best bet is to pull something from a catalog and get it off the shelf. This applies with both unibody and modular. But a tight time frame, price concerns, and the need for custom design changes things. Modular offers many more options while still using a standard solution through use of accessories and options. It is also easier to manufacture a modular enclosure of a special size as the processes are highly automated and size deviation on a modular frame is relatively simple. All in all, modular provides endless options and accessories — all standard.