RAST connectors include signal and power designs based on insulation displacement technology. The original specification included a maximum of 12 contacts, but RAST connectors are currently available with 20 or more contacts. They were developed for consumer white goods and have been adopted by various applications, including automotive systems.
The RAST connector system was designed to be assembled with automatic equipment to ensure high quality and support high production volumes for use in applications that don’t require a high number of mating/unmating cycles. They are available in several contact formats and styles, including wire-to-board, wire-to-wire, and wire-to-panel formats with insulation displacement connections (IDC), sometimes called insulation-piercing contacts (IPC) or insulation displacement terminals (IDT), and with crimp contacts.
This FAQ reviews the RAST standard and how it relates to appliances like HVAC and white goods and automotive applications like LED lighting and looks at the connectors included and how the range of connectors has expanded over time.
RAST is a de facto connector standard from the German Raster Anschluss Steck Technik, or “grid connection plug technology” in English. It was developed by a group of European home appliance manufacturers, including AEG (Electrolux), Bauknecht (Whirlpool), Bosch, Miele, Siemens Hausgeräte, and AEG (Electrolux), together with connector makers like AMP (TE Connectivity), Lumberg, Molex, Stocko Contact GmbH, and Wieland Electric, under the coordination of the Central Association of the Electrical Engineering and Electronics Industry (Zentralverband Elektrotechnik- und Elektronikindustrie, or ZVEI). It was finalized in 1986 and has evolved in an ad hoc manner since.
RAST nomenclature includes the word “RAST” followed by a number, like RAST 5. The number indicates the centerline spacing of the contacts. The original standard included RAST 2.5 and RAST 5 connectors, with centerline spacings of 2.5 and 5 mm, respectively. More recently, RAST 1.5 and RAST 7.5 designs have been added. Common RAST connectors include RAST 2.5 designs rated for 2 A and 4 A for signal contacts and 10 A for power contacts and RAST 5 designs rated for 16 A. RAST 1.5 was developed to provide a higher-density solution and usually has contacts rated for 1 A. RAST 7.5 targets higher power applications and has contacts rated for 25 A or higher.
The standard includes basic connector specifications like housing geometries and dimensions, tabs (also called coding lugs) to identify specific connector types like RAST 2.5 versus RAST 5, polarization features to prevent incorrect assembly, and some designs include optional housing color coding for easy identification or external latching mechanisms for increased robustness (Figure 1).
The RAST system was developed to achieve several design goals, including:
- Reducing the variety of components in harness assemblies.
- The option to customize the keying and polarization features using automatic termination equipment further reduces the number of parts that are kept in inventory.
- Reduction in plugging errors using polarization.
- A latching system to improve connector retention and system reliability.
- Reducing labor costs compared with the previous crimp-style contacts since the IEC contacts are suited for use in automated harness-making equipment.
These features make RAST connectors suitable for various white goods and HVAC applications, including rotary switches, pressure sensors, relays, pumps, etc. They are also used to provide interconnects for PCBs in motor controls.
After the initial introduction, RAST 5 connectors lost some market share when designers discovered that RAST 2.5 connectors could be used in higher voltage applications simply by using every second contact to carry power and using the intervening contacts for added isolation. That strategy successfully reduced the part numbers in inventory until current levels exceeded the ratings of RAST 2.5 contacts. Designers returned to using RAST 5 connectors and developed the newer RAST 7.5 connectors, sometimes called RAST Power, for even higher current ratings (Figure 2).
Additional features of the RAST connector system include:
- Mating headers with vertical and right-angle orientations
- Surface mount versions have been added to the original through-hole PCB mount design.
- Colors have been added to simplify connector identification, especially in complex wiring harnesses and hand assembly operations.
- Mounting can be made directly on the PCB or with headers. Mounting the connectors on the PCB can reduce assembly costs and speed system integration.
- Polarizing ribs on the bottom latches on the side and various types of locks ensure proper polarization for improved assemblies. Some series have several PCB footprint keying options like in-line, staggered, and reverse staggered.
- RAST connectors are available for various wire types, including ribbon cables, increasing design flexibility.
Getting better with more options
While the formal standardization effort has long been disbanded, connector suppliers and makers of automated assembly equipment continue to evolve and improve the RAST system. The original IDC terminations are widely used, and the system has expanded to include double IDC slot contacts to support daisy chaining in wiring harnesses (Figure 3). Crimp and screw-type connections have also been added.
RAST power connectors have evolved to include new contact geometries like 4 points of contact at the mating surface and contacts with high normal forces for reliable high current interconnects. RAST connectors are available with the latest materials that meet the requirements of IEC and UL needle flame and glow wire flammability testing and UL V-0 ratings. They have various plating options, including tin for lower-cost solutions and silver for higher performance.
The European white goods industry developed RAST connectors. It’s an industry standard that has continued to develop in an ad hoc manner to include more pinout options, high contact densities, higher current solutions, and other features to meet the evolving needs of applications ranging from white goods to HVAC systems and automotive applications like LED lighting.