Скачать или смотреть Plessey 15/3 private Automatic Exchange using uniselectors

Prior to the 1980s, telephone installation in Australia was the exclusive preserve of the Postmaster Generals department (PMG). In the 1960’s the only product the PMG could offer the NSW Education department for schools was a manual telephone exchange system. Automatic equivalents were way too large and expensive to justify installation in a typical high school campus.

Because of this, the education department embarked on a program of obtaining its own “private automatic exchange” equipment on the private market. This would typically be installed alongside the manual PMG solution using separate cabling. Since this private system was not interconnected with the PMG’s lines in any way whatsoever, it “got around” a exclusive legal requirement at the time which prohibited anyone else but the publicly owned PMG from installing telephones in buildings.

Typically two separate telephones would be located in each staff room of a school, one to “dial out” of the school (through the manual exchange in the main office) and another to dial and communicate with other staff within the campus through this equipment. The ultimate irony was that in most cases, this equipment ended up being installed and maintained by the PMG’s department anyway, under contract to the private firm “PAX Telephones” who in turn held the contract with the NSW Education department!

The units use three groups of two 25 point uniselectors, one acting as a line finder and the other as a final selector arranged in a “2+4” numbering scheme to provide the switching function so that up to three conversations could be made through the unit at any one time. By the early 1980s, the legal situation changed allowing private operators into the public system, resulting in these systems all being replaced by electronic “key station” systems by 1985.