On November 23rd 1964 a new telephone exchange was brought into service at Broughton near Preston. Unlike all other automatic exchanges in the UK at this time, Broughton was a Crossbar system. To mark the 50th anniversary, here we look through some of the material The Communications Museum Trust has in it's archives and explain what Crossbar was.
The British General Post Office (GPO) had resisted adopting crossbar up until this point, preferring to stick with Strowger until a viable electronic system could be developed. The three suppliers of switching equipment to the GPO (Plessey, GEC & STC) however faced a problem. The rest of the world had adopted crossbar and export orders for Strowger were declining. The Plessey research and production site at Edge Lane Liverpool had therefore developed a crossbar switching system called 5005 which they hoped to sell to export customers and were pushing the GPO to adopt it in the UK as well.
With demand for phone service rising, there was a growing waiting list of customers. There were also delays to the introduction of electronic exchanges in the aftermath of the Highgate Wood experiment
Therefore the GPO agreed to a field trial of a Plessey 5005 crossbar system which would serve two purposes - give the GPO experience of operating a crossbar system and give Plessey a real-world exchange which they could show to potential overseas customers.
The site was chosen to be as close as possible to Plesseys Liverpool site where the engineers who designed it and sales people who would be selling it, were based. Broughton, a few miles north of Preston, had a manual exchange which at the time was serving around 700 lines and was scheduled for replacement with a Plessey Strowger automatic system. Plans were already underway to build a new H type building to house the automatic exchange and a decision was made to install Plessey 5005 crossbar instead of the Strowger, with a planned Brought Into Service date of November 23rd 1964
New exchanges are typically designed to expand to handle the anticipated traffic and number of lines over a 20 year period. This gave Broughton's new exchange a planned ultimate capacity of 2500 lines, with an initial installation to cater for 1200. By 1973 it was serving 1800 lines and by 1983 it was serving 2800.
With the large reed-relay electronic system delayed (it would not be ready until 1976) the success of the Broughton field trial convinced the GPO to adopt the Plessey 5005 crossbar system for installation nationwide with rollout starting in 1968 (The first being at Bacup, Lancashire). The Broughton equipment would remain in service until August 11th 1993 when it was replaced with an Ericsson AXE digital exchange remote concentrator.
The last Crossbar system in the UK was removed from service at Droitwich in March 1994.