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Eights aren't so crazy after all

Eights aren't so crazy after all

Springfield, OH -Naming a new rail system TS8 after the figure eight it reveals in cross section, Rittal Corp., with headquarters in Herborn, Germany, claims a 30% improvement in enclosure rigidity and stability for the new profile. According to Walter Nicolai, who led the team that invented the profile, the new shape brings a 15% reduction in material use along with increased stiffness over a previous design.

Why does the rigidity of an enclosure frame matter to engineers? Explains Product Manager Mike Murphy: "In 98% of applications, people are populating the box with something on the mounting panels-mostly control components, drives, and bus bars. These represent significant weight for an enclosure, he says. "And during transport, there is a lot of shear and potential twisting as you lift and move the enclosure."

For users of traditional welded unibody boxes, Murphy says, mounting panel capacity and torsional rigidity aren't major issues. That is to say, strength is an issue, but engineers here have come to trust the design of the traditional fabricated cabinet. And while some skeptics may question the strength of a modular enclosure, Europeans, who are used to working with such designs, take it as a given. For them, the benefits of easy baying needs no underlining. Add to that list the flexibility of modular design-unmatched by unibody cabinetry.

The figure eight profile stems from development efforts dating back six years ago, according to Murphy. By then, a modular enclosure designated PS, which Rittal had begun selling in 1985, had attracted quite a pile of user comments.

Many customers were looking for symmetry in hopes of being able to join, or bay, one cabinet to a second along any face, rather than on the sides only. In response, engineers set out to find a profile from which such a symmetrical enclosure could be fashioned. At the same time, they insisted that the new design be manufactured easily and be as strong as, or stronger than, existing products. Cost reduction was important, too.

It took 40 tries to get it right, Murphy says. What evolved finally was a 16-sided profile, which actually is not as structurally rigid in the vertical axis as the older PS frame members were, he says. It's only after individual pieces assemble into an electrical enclosure that the design shows off its strength.

The PS corner used a three-prong joint to connect horizontal and vertical pieces, with all three fingers connected to identical profiles. An inside weld bonded the assembly together, he adds. In contrast, no corner piece graces the new TS. Instead, a rectangular steel block serves as a key to align all three axes. Plasma welds on the outside of the joint and MIG welds inside hold the corner fast.

One challenge in developing the TS8 profile, explains Nicolai, was managing the trade off between the higher moment of inertia inherent in closed holes and the better manufacturability of formed holes that are left open. According to Rittal test data, the PS profile doubles in one plane, and nearly quadruples in another, the moment of inertia of the TS profile. But forming the TS takes strip coil a mere 154 mm wide; the PS needs 200 mm to shape up. Another difference: the PS doubles back along the seam to complete the profile; the TS relies on a laser weld every 4 inches to tack down its folds.

Kevin Jones, a senior electrical designer at Cincinnati-based Pak/Teem Inc., said he chose TS8 enclosures over PS models on a recent integration project because the TS8 came more fully assembled for less cost. The specification called for Rittal enclosures but left model choice to the integrator, Jones says.

One of the key features of the TS8 enclosure for this particular project-which Jones said required CE markings though it is destined for a U.S. site-was its base plinth design. The control cabinets will all be installed on a second story mezzanine, he explains. All cables and conductors will run up through the bottom of the enclosure rather than down from the top-the traditional method. The TS base accommodates this unusual routing, he says.

Engineers might want to turn their attention towards this product for another reason, Murphy says. Much tele- and data-communications equipment is going into earthquake prone regions. Many of these components ride in 19-inch rack mounts, Murphy says, a popular TS8 configuration. The standard TS8 enclosure is certified to handle up to 330 lbs in seismic zone 3 areas. With an enhanced base, or plinth, the same enclosure can protect 400 lbs of equipment in a zone 4 seismic area. And, adding stiffeners to the doors, corners, and sides raises zone 4 enclosure capacity to 1,100 lbs.

Additional Details

Contact Michael Murphy, Rittal Corp., 1 Rittal Place, Springfield, OH 45504; Tel: (800) 477-4000; Fax: (973) 390-5599; or Enter 501

Typical Applications

Process and heavy industry

Environments requiring EMI protection

Data and telecommunications

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