DIN Rail Basics

If you deal with electrical installations for industrial control applications, no doubt you have heard the term DIN rail or have used DIN rail in your installations. Perhaps you have even read an article or two regarding some of the products that mount on DIN rail, such as terminal blocks or contactors. While much time has been spent educating customers on DIN rail mountable products, very little time has been spent on the backbone of this system, DIN rail itself. By gaining a valuable understanding of DIN rail applications in a control environment, such as materials available, options, and foot prints, new and long time users of DIN rail can better utilize this industry standard.

DIN, an acronym for "Deutsche Institute von Normen" or "German Institute of Standards", is a worldwide standard ensuring dimensional uniformity for products regardless of the manufacturer. DIN rail is the metal rail used to mount various electrical components (for example, terminal blocks, motor starters, relays, circuit breakers, contactors, remote I/O, power supplies, etc..) in a control cabinet. Since the rail is manufactured to DIN standards, end users can select DIN rail mountable product from different manufacturers (for example, terminal blocks from XYZ Corporation and contactors from ABC Corporation) and mount them on the same rail. This gives the end user the freedom to specify the electrical components desired without concern for being committed to a single supplier due to the mounting rail (Warning: be careful of using proprietary mounting rails which do not conform to DIN standards). In addition, the use of DIN rail saves time and space (no need to panel mount all components), as well as, provides a central location where external and internal wiring can be connected quickly and efficiently.

MATERIALS

DIN rail is available in various base metals of which, the most common are steel, aluminum, stainless-steel and copper. In addition, DIN rail is available in various finishes with respect to the base metal. The most common base metal and finish combination in the industry is zinc plated, yellow chromated steel. Zinc is less noble than steel and will sacrifice itself for the protection of the base metal against the elements/corrosion. The yellow chromate protects the zinc plating against wear and formation of zinc oxide. However, selection of metal type depends on the application.

When selecting a DIN rail with specific metal composition, several factors must be considered; enclosure/control cabinet material, environment (usually already determined with the selection of enclosure material), products to be mounted and short circuit requirements for grounding. For example, if you have selected an aluminum enclosure, an aluminum DIN rail should be selected. The aluminum enclosure was probably selected due to a corrosive or damp environment and deviating from this material spec on the DIN rail could cause the exact situation (corrosion) you were trying to avoid. Using dissimilar metals (aluminum enclosure and steel DIN rail) creates what is called a galvanic cell which, can lead to galvanic corrosion. Galvanic corrosion causes eventual deterioration of the aluminum enclosure and can cause electrical grounding problems. If mounting heavy components, such as large PLC's, steel rail is the best bet due to its strength and durability. And although all metal rails can be used as a ground busbar, copper DIN rail provide the optimum in conductance for creating a path to ground. For a quick reference guide for specify DIN rail metals see figure XXX.

FOOT PRINT

In addition to material specs, DIN rail is available in a variety of different footprints. There are three main footprints available; TS-32, TS-35, and TS-15.

When selecting a footprint, make sure that all the components specified accommodate the footprint. A complete representation of all profiles/foot prints is shown in figure XXX.

MOUNTING OPTIONS

DIN rail is also available with or without mounting slots. Pre-manufactured mounting slots come in two different configuration, standard (6.3 x 18mm slots) or long slots (5.2 x 25mm slots). These pre-manufactured slots allow for quick and easy fastening of the DIN rail into the enclosure and eliminates the need for a punching tool. Most suppliers of DIN rail offer custom punched holes to customer spec as well. Additional value added services offered include, PEM stud mounted and cut to length DIN rail (standard DIN rail lengths are 2 meters and 1meter). These services are beneficial if you lack the tools required to punching and cutting rail or just want to reduce installation time.

GROUNDING BUSBAR

With the use of a DIN rail ground (protective conductor) terminal block, the DIN rail itself can be used as the grounding busbar. The following is an illustration of how the system works to create a path to ground; the ground terminal has a metal foot that bits into the DIN rail, the rail is fastened to the enclosure, and the enclosure is connected to earth ground. This system allows all control components and their ground requirements to be placed on the same rail and in the same location (a separate ground busbar is no longer required). The benefits of this include reducing installation costs, saving panel space and allowing for quick and easy trouble shooting. When using DIN rail as a ground busbar, particular attention must be paid to the short circuit properties of the rail. Short circuit properties of the rail will depend on the metal material and the surface area of the rail (relating back to foot print). A reference on short circuit properties of DIN rail and short circuit calculation can be found in figure XXX.

CONCLUSION

As you can see by now, there is more thought required to specifying DIN rail than asking, "Do my components fit on this rail?" Using DIN rail in your next control panel design, can save time, money and give a professional appearance to the job. However, some time must be spent ensuring the best option to fit the application considering; environmental issues, galvanic corrosion, short circuit requirements, and mounting options.

Metal Selection

Short Circuit Properties

*Per UL 1059, mounting rails of a protective conductor terminal block intended to be connected to a busbar designated as the protective conductor shall be of steel, copper alloy, or aluminum alloy.

Formula: S= Square root of l² x t divided by k

S = minimum cross section in mm²or AWG

I = short circuit current in amperes

T = reaction time of switch-off in s

K = material coefficient

For more information, contact Dean Norton, [email protected], or call (910) 259-5050 or (800) WIELAND, or Enter 544.

Dean Norton is the VP of Marketing at WAGO Corporation