CMS:Completing Marker 0 (CM0)

Completing Marker 0 (CM0) is a marker in the 5XB switch at Connections Museum in Seattle. It is one of two completing markers in the 5XB, and one of three markers overall in that exchange.

A wide-angle view of CM0 (left side), consisting of four bays. Note the bay farthest left with cross-connect fields, and the several bays of relays to the right of it.

Completing Marker 0 (SD-26002-01) is a wirespring type, named for its extensive use of wirespring relays. This is in contrast to Completing Marker 1, which is an older U&Y type, using U&Y "flatspring" type relays. CM0 was part of the original 5XB as it existed in the Adams exchange on Mercer Island. It was manufactured by Western Electric in 1957. It consists of four bays of equipment, plus a route relay frame shared with the other two markers. The two leftmost bays are Translator & Code Treatment (T&CT) bays, and the two rightmost are Common Equipment (CE) bay, which contains most of the shared relay logic.

Notably, CM0 contains most of the leaky potted relays in the 5XB. Most of these were repaired by Sarah Autumn in 2024, however some still leak on occasion and must be checked regularly.