Mechanical Switching

In almost every neighborhood there is a windowless building that houses the switching equipment that connects your telephone to your neighbor’s telephone or routes your call to another central office for long distance calls. This building is called the central office. The switching equipment is located on panels in the central office. The museum has six operational panels of different vintages on display.

Master Test Frame for #1 and #5 Crossbar Switch

This frame uses relays to test other frame circuits. Today the equipment is computerized and is uses digital components. Our modern computers are direct descendents of the switches developed for telephone circuits.

#5 Crossbar Frames

This view of the #5 crossbar shows several frames one behind the other. The frame that is closest in the photograph is the automatic monitor test frame. The frame just behind it is the master timer that tallies the toll charges for subscribers. The next frame after that is the automatic test frame.

Panel Final Frame

This is a close up of a panel final frame it shows a terminal bank and select rods and the rotary sequence switches unique to the panel office. The rods are driven by electric motors and clutches and move up and down to make connections. On the left of this photograph, sequence switches control the operation of the rods. This office has been returned to operational condition and is thought to be the only operational unit remaining in the world.

Community Dial Office

This community dial office utilizes Strowger designed switches. These switches were manufactured by Western Electric. These rotary switches had contacts that were 10 switches high each with 10 positions. Pulses created from the subscriber’s rotary dialer cause the switches to rotate and connect to the next series of switches for each digit that was dialed. The Strowger equipment shown was originally installed in Crystal Mountain, Sumner and Belfair, Washington. Pieces of equipment were assembled to create this working display.

Main Distribution Frame

The main distribution frame (MDF) is located in the central office (CO). This frame terminates (connects) all the wires and cables that enter or exit the central office. The MDF contains fusible links to protect equipment from damage from lighting or other voltage surges.