RAST - the old/new appliance standard

The global market for connectors used in consumer applications is expected to top $2.8 billion by 2013. A key segment of the consumer market is the household appliance, or whitegoods, industry.

Encompassing a variety of items we use daily, the whitegoods industry includes washing machines and dryers, refrigerators, microwaves, freezers, dishwashers, compactors and cookers, all generally referred to as major appliances.

It also includes small appliances, such as coffeemakers, mixers and toasters. These products are usually taken for granted until they stop working, but consumers are taking a greater interest in the category, due to improved designs that offer new convenience and safety features and consume less energy.

Many of these improvements have been spurred by the increased use of electronics in appliances over the last 10 years.

For instance, some new refrigerators do more than just keep your food cold; they feature TV, radio and internet access. You can look up recipes online and charge your mobile phone, MP3 player or DVD/CD player while you cook. While that model may not be in everyone’s home, other cutting-edge features are becoming commonplace.

Today, dishwashers rely less on chemicals for cleaning but instead count on higher water temperature to sanitise and clean. Dishwashers also use far less water and energy than units produced even 10 years ago and many, especially in Europe, incorporate heat-recovery systems that use the steam generated by the machine to heat incoming rinse water.

Another innovation is energy management, which enables appliances to receive signals from the utility and, using an internal program, regulate when operations such as frost modes on a refrigerator are performed, which reduces energy consumption during more expensive peak hours.

Two key factors in the increased use of electronics in appliances are standardisation and modularisation. In the realm of standardisation, the most influential connector system is the RAST system.

These connectors were developed more than two decades ago in Europe as a way to standardise components, ensure intermateability among manufacturers and reduce plugging errors. The RAST systems, like the appliance industry, have undergone a transformation in the last decade.

RAST, says Lee Thomas, industry marketing manager, home appliances at Molex, “is the acronym for Raster Anschluss Steck Tecknik, roughly translated from German as ‘pitch connection plug technology’.

Controlled by the ZVEI (Zentralverbank Elektrotechnik-und Elektronikindustrie e.V, German Electrical and Electronic Manufacturers’ Association) committee, RAST connectors form the connection system for the multiple sensor, switch, actuator and motor drive wires that connect to the control board.

Initially developed using a crimp-style contact - in which the wire was stripped, crimped and snapped into a plastic housing - many of today’s RAST system components now incorporate an insulation displacement termination contact that allows termination of the wire without stripping or crimping.

Because the contacts are pre-assembled in the housing, there are fewer components to worry about and less chance of wires being inadvertently snapped into the wrong position. These advantages broaden the RAST system’s appeal and potential.

Developed around two contact pitch configurations, 2.50 and 5 mm, the connectors are available in a variety of versions, with multiple keying, coding and locking options.

“The Molex line-up includes 5 IDT and crimp for indirect mating in either 10 or 16 A versions. RAST 2.5 for direct and indirect mating and Power for direct and indirect mating in both 6 and 10 A versions,” said Thomas.

“Optional polarising ribs, colour coding, side latches and pip locks and offered throughout the range, in addition to open or slotted sidewalls on the 2.5 and Power connectors.

“To complement its range, Molex also offers mating headers in vertical and right-angle versions.

In addition to thru-hole PCB-mount products, many European manufacturers also offer surface-mount versions. STOCKO Contact, the first company in Europe to offer surface-mount RAST connectors, has a product made of DSM Engineering Plastic’s high-performance Stanyl Fortii.

Use of this material allows connectors to be assembled on the board by lead-free reflow soldering, reducing assembly time.

Modularisation, the second key factor that has influenced electronics features in appliances, is also supported extensively through the RAST system. As more and more features are added to an appliance, the number of connectors increases, as each of these features must be connected to the control panel.

Rather than use individual connectors and harnesses, RAST provides the ability to gang up connections, reducing the number of harnesses. Using both colour-coded and uniquely keyed and polarised connectors, the system reduces assembly time and the chance of mis-wiring, while reducing the number of components a manufacturer has to keep in inventory.

Reducing the number of components in an inventory is especially advantageous in North America when a consumer or business owner requires repair on a domestically manufactured product. Due to a lack of standardisation, service centres that support repairs are often required to carry a much wider range of parts to satisfy a large number of manufacturers.

Lack of standardisation is even more noticeable to the North American consumer when the required repair is on an appliance assembled in China or the Asia-Pacific region.

Because of the broad number of manufacturers who supply components to the whitegoods industry, it is not uncommon for a consumer to wait weeks while a part is ordered and shipped from overseas.

Although the RAST connector system is still primarily in use in Europe, many signs indicate that, as the benefits of the system become more apparent, other countries will adopt it as well. According to Thomas, “The new global interest in the RAST system is based both on process improvements and cost savings.

“Automated IDT systems not only add speed to the wire harness assembly but also provide testing to lower the applied costs in the manufacturing process. As IDT typically uses an automated process, harness failures are significantly lowered compared with manually built harnesses, which are normally crimp-and-poke-type systems.

“A harness failure can be extremely costly for a manufacturer when considering the rework costs to replace a failed connector on a harness that is already loaded into an appliance.”

Another reason the RAST systems have not become as prevalent in other countries, primarily Asia and China, is that, unlike other industries, in the whitegoods industry, geographic presence plays a much larger role in shaping product types and preferences.

In North America, it is not uncommon to have a large washer and dryer. The average American home is designed with a separate area just for doing laundry. But go to China, a country with the greatest population in the world, and space is at such a premium that most Chinese families live in small apartments.

“In China, stacking or compact units are more prevalent,” says Brian Krause, vice-president of marketing and communications for Molex.

“In Asia, the acceptance of RAST by OEMs is somewhat limited to global OEMs selling into the market. At present, the relatively inexpensive labour in the region, coupled with the low capital expenditure, does not make the transition from the manual crimp-and-poke-type systems to automated RAST systems cost effective.

“In the future, Asian OEMs may adopt a RAST crimp/RAST IDT hybrid concept for them to adopt new technologies and better serve their growing indigenous market,” said Thomas.

Driving both their indigenous market and the international market is exactly what China-based Leoco is doing. One of the few Chinese connector manufacturers to offer RAST connectors, the company only offers the crimp RAST 5 wire-to-board connector in two to 12 positions but Claire Chang, sales director for Leoco US, said the 2.5 RAST and the IDC RAST are both currently under development.”

Chang also acknowledges that although its primary customers are European, they do work extensively with Chinese-based contract manufacturers who are buying and assembling parts for European customers.

Notably, rather than being used in a major appliance, such as a washer, dryer or refrigerator, the company’s RAST products are currently used in smaller appliances, designed for both commercial and consumer use.

The ability to satisfy local safety standards is also very important when dealing with manufactured equipment, especially equipment such as appliances that are geared primarily towards consumer use.

In North America, this means being able to satisfy UL and CSA standards, in particular, UL94V-0. UL94V-0 evaluates the combustion of a particular item when brought in contact with a direct flame. To satisfy UL94V-0 requirements, a flame must be out in 10 seconds or less, no glow must be visible beyond 30 seconds and no burning material can fall from the flame.

In Europe, this means not only being able to satisfy TÜV standards but also IEC 60335-1, fourth edition. IEC 60335-1, fourth edition, often referred to as the Glow-Wire European safety standard, is much more stringent than UL94V-0 requirements in that it covers both direct flame and indirect flames.

“This certification is required on all home appliances sold in Europe. The Glow-Wire standard acts as protection against fire for unattended electrical household appliances. The test is designed to identify plastic materials that could ignite when wires are overloaded.

“To pass the test, a connector is submitted to a glow wire at 750°C for 30 seconds. There can be no ignition, or any flames must self-extinguish within two seconds,” said Thomas.

Chang also acknowledges the importance of satisfying the European Glow-Wire safety standard.

One additional driving force behind the increased use of RAST worldwide is the number of component manufacturers and subassembly manufacturers now incorporating built-in RAST headers and terminals in their products.

Robin Pearce, Bishop & Associates
rpearce@bishopinc.com