Western Electric 355 A

The Western Electric 355 A is a Strowger step-by-step telephone switch. It uses the same principles as the original device patented by Almon Strowger in 1891, where electric pulses are used to step selectors up a number of times to make a telephone connection. The 355 A features improvements over Strowger's original design such as compact line finders and trunk equipment for connecting to other switching offices.

355 As required constant maintenance to continue running but were also reliable enough to remain in service for decades. Some were still in service as late as the 1980s.