Rotary system

The Rotary machine switching system was a type of automatic telephone exchange manufactured and used in Europe from the 1910s. It was developed by Bell Labs in America when they were developing the Panel system [ Fagen, M.D. "A History of Engineering and Science in the Bell System; The Early Years (1875-1925)" (1975, Bell Telephone Laboratories) pages 581, 607. ] . The Rotary and Panel systems had many features in common eg machine driven switches and sequence switches powered via shafts and clutches, and revertive impulsing from the switches back to the controlling Register which received the dial impulses; but the switches were smaller (200 rather than 500 outlets). The initial version was called 7A, succeeded by 7A1 and then 7A2; with a 7D rural system also.

While the Panel system was chosen for American large cities, the Rotary system was selected for use in Europe and manufactured at the Bell Telephone Manufacturing (Western Electric) factory in Antwerp, Belgium. The first exchanges were installed in England at Darlington (10 October 1914) and Dudley (9 September 1916). However the British Post Office standardised on the Step-by-Step (SXS) system in 1922, and subsequently the SXS Director system for London and other large cities. Rotary exchanges were used by Hull (where telephone service was not supplied by of the BPO).

The Rotary system was chosen for The Hague, Holland and New Zealand in 1913-14, but manufacture was disrupted by the German invasion of Belgium. Dies were moved to England, then to the Hawthorne Works of Western Electric in America (manufacture resumed at Antwerp in 1920). The first exchanges cutover were Masterton, New Zealand on 31 May 1919 (followed by Courtenay Place and Wellington South in Wellington on 18 October 1919) [ Shrimpton, E.A. "The 7-A Rotary Machine Switching System in New Zealand" (Electrical Communication Volume VI Number 2, October 1927) ] and Scheveningen, The Hague on 7 January, 1920 [ Turkhud, B.A. "The Hague Telephone Network" (Electrical Communication Volume 4 Number 4) ] . The Hague was the first multi-office area served entirely by the No. 7-A machine system with the cutover of the new Centrum office on 15 February 1924. There were four offices equipped with 23,000 lines; Bezuidenhout, Centrum (or Hofstraat), Hague West (or Marnix), and Scheveningen. The system was owned by The Hague Municipality; initially only 5000 lines were fully automatic, the rest were semi-automatic.

In 1925 IT&T purchased the Bell Telephone Manufacturing company in Belgium, which was formerly affiliated with AT&T; as the Bell System agreed with regulators to sell its overseas manufacturing interests. In the 1930s, ITT grew through purchasing German electronic companies Standard Elektrizitaetsgesellschaft and Mix & Genest, both of which were internationally active companies.

Apart from Holland (38,100 lines) and New Zealand (48,400 lines), other countries who had installed or ordered Rotary equipment by 1925 [ Deakin, Gerald "No. 7-A Machine Switching System" (Electrical Communication Volume III Number 3, January 1925) ] were Australia, Belgium (29,000 lines), Denmark, England, France, Hungary, Italy, Norway (41,160 lines), Romania, South Africa, Sweden and Switzerland. There was a total of 104,615 lines in service, and 137,330 lines “proceeding”. Subsequently at Zurich, Switzerland; the mechanical registers were replaced by PDP computers.

The Rotary system used 1st and 2nd linefinders; when a customer picked up the phone all free linefinders in the group drove until one picked that customer line. Calls were switched over two, three or four group selection stages followed by a final selector. An office could start with two group selection stages for local calls (a first group level would serve 2000 lines), and be expanded to three group selection stages if it outgrew say 2000 or 4000 lines, depending on the number of first group levels required for other offices in a multi-exchange area.

References

*Note: Electrical Communication was published quarterly by the International Standard Electric Corporation. Subsidiaries of the company included the Bell Telephone Manufacturing Company, Antwerp and Standard Electric or Standard Telephones and Cables in various countries. Deakin and Turkhud were with the Bell Telephone Manufacturing Company, Antwerp; Shrimpton was with Standard Telephones and Cables (Australasia).

External links

* [http://web.ukonline.co.uk/freshwater/histuk.htm UK Telephone History]