Electromechanical switching systems

Strowger is an electromechanical telephone switching system, known by the name Strowger in Britain and some English-speaking territories, and as ‘step’ or Step-by-Step (SxS) in North America.

Strowger 2 motion selectors (Photo BT Archive TCB_417E13309)

Although obsolescent now, it was once the most widely used telephone switching technology in the world. 


Almon Brown Strowger is the man credited with inventing this system in the late 19th century. As with so many ‘inventions’, the development work was not his entirely unaided work, but his was the first fully automatic switch to achieve commercial success and he certainly made the system what it is today.

And how do you pronounce Strowger? ‘ow’ as in ‘lower’ and the ‘G’ as a ‘J’.

Almon Brown Stowger

What was so special about STROWGER?

A maintenance engineer recalls; ‘You could compare Strowger with the appeal for steam trains- added dimensions of smell and sound! I remember well, being in an exchange late at night and hearing a single call progress its way through the exchange, selector by selector.   The smell of a stuck and overheating rotary magnet on a 2000 selector  as  you  walked  past the rack, then using your nose to locate it!’

How about the racket that Registers made in a busy GSC (Group Switching Centre) and the pile of brass  filings under the over-worked ‘send’ uniselector ? Or the sound of a group selector bending it’s wipers as it tries to go rotary and ends up clacking away because the wipers have gone out of adjustment and it can’t enter the bank.

All these type of things made the job more than just plain routine. The whole exchange seemed to have a life of it’s own, and as you got more experienced, you used all of your senses to look after the place. Marvellous really !

Strowger is heavy; most telephone exchanges had specially reinforced floors to carry the fantastic load of rack upon rack crammed with relays sets and selectors fitted in wherever space allowed. 
Photo BT Archive TCB_417_35808.                   

Thanks to Kevin, Andy Emmerson and Dave Milner for their contributions.