500 switch father

Kåell, Knut, engineer (portrait, 1930s)
Knut Kåell, engineer and inventor. Worked for LM Ericsson 1911-1958. Took an active part in the development and marketing of the 500 point selector in the 1920s, and ended up as director.

In 1918, telecom engineer Knut Kåell was appointed manager of the department for automatic stations at Ericsson. Here he would refine the ideas for an automatic telephone system that Axel Hultman had developed within Televerket, the Swedish PTT. The smooth multiple bars were unique and ingenious, but the large switch, which was originally dimensioned for 10,000 lines was unwieldy. Kåell determined that the multiple size should be 500 lines. Hultman’s first switch was designed around two movements at right angles, but Kåell believed that the switch would be simpler and more reliable if a rotary movement was used, followed by a spiral movement. These ideas resulted in the renowned 500-switch, which would be the company’s main product for 1decades.

The first station using the 500-switching system was taken into operation in Rotterdam in 1923 and was installed under Kåell’s personal supervision.

Knut Kåell was born in Timrå in 1887. His name was originally Knut Larsson, but he took the surname Kåell based on the initials K and L. His wife Sigrid’s maiden name was Olsson. The couple had two sons, who both became engineers. Kåell’s son Åke joined Ericsson in 1939 and was appointed manager of the technical equipment department in 1955.

Knut Kåell remained with Ericsson until 1959. In recognition of the company’s appreciation of his work in telephone technology, he was presented with the one millionth 500-switch to be manufactured, an award which he valued highly. Knut Kåell died in 1962.

 Author: K V Tahvanainen


Switch, 500 point selector, drawing, 1922

© Telefonaktiebolaget LM Ericsson and Centre for Business History

Contact info/About the site