Panel switch

The panel switching system was an early type of automatic telephone exchange, first put into urban service by the Bell System in the 1920s and removed during the 1970s. The Panel and Rotary systems were developed in parallel by Bell Labs before World War I, and had many features in common, though the Rotary system was used in Europe.

The first Panel exchange was installed at the Mulberry Central Office in Newark, New Jersey. It was placed in service on January 16, 1915. It was a semi-automatic system using non-dial telephones. The next installation was in the Waverly C.O. June 12th. of the same year, also in Newark, NJ.

The Panel Machine Switching System (M.S.S.) was named for its tall panels covered with 500 rows of terminals. Each panel had an electric motor, to drive its (usually sixty) selectors by electromagnetically controlled clutches. The selector was similar in effect to a stepping switch though it moved continuously rather than in steps. Each selector had five brushes, any of which had 100 terminals among which it could select, arranged in groups. Pulses were sent back from the selector to a Register which had received the dialled digits, rather than forward as in the SXS system, hence the signaling was called "Revertive Pulse".

Telephone numbering

As in the SXS system, each installed office could handle up to 10,000 numbered lines, requiring four digits for a line number within...
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