25 years ago, ZIEHL-ABEGG laid the foundations for the launch of energysaving EC motors in ventilation technology. This came as the result of Germany’s telephone exchanges changing to digital technology that required safe and reliable cooling of the operating rooms. The Austrian post and telegraph administration service also moved to this technology in the 1990s. Until then, fans in ventilation systems were driven using uncontrolled asynchronous motors. ZIEHL-ABEGG had been working on mains-powered electronically commutated DC motor (EC) drives. But the much higher costs had prevented them from being used en masse. In 1989 came the first serious discussions with Hansa, a company that made air conditioning units, about the use of the new motors for the postal service. RD40K-4KW.4R.1L was the type designation of the first fan fitted with EC motors. The first serial products were delivered in 1991 and were used in the digital exchanges at the Deutsche Bundespost. Due to their high efficiency, EC fans from ZIEHL-ABEGG were increasingly used by leadingmanufacturers of digital exchanges.