S.T.C. Type 4200-D
P.A.B.X.

Used by other telephone administrations

This is based on the principles of this company's well known Rotary Public Exchange system, in which the selectors and line finders are power driven through gears from a shaft operated by an electric motor. A small " marker " switch is also employed and this is the only switch controlled by dialled impulses.

The equipment is manufactured in loo line units, each unit being 7' 5" high, 3' 10" wide and 2' 4" deep. Space in each unit is left for the addition of an auxiliary unit which when fitted allows two additional too line units to be interconnected with the first, the capacity of the installation being increased thereby to 300 lines. Two, three or four too line units may be inter-connected in this manner, thus increasing the capacity ultimately to 400 lines, and only two auxiliary selector units are required for this purpose.

Each 100 line unit is wired for a maximum of:-
100 - extension line circuits, each of 2 relays.
13 - connecting circuits, each comprising one line finder, one final selector, one sequence switch, one marker switch and associated relays.
1 - Starting circuit.
1 - Ringing and tone circuit.
1 - Traffic metering circuit.
1 - Alarm circuit.
13 - Auxiliary final selectors (only required when the equipment exceeds or will exceed too lines).

The initial quantity of equipment fitted is determined by traffic requirements.

The 1/30 h.p. motor driving the shafting may be arranged to start up when a call is originated or to run continuously if desirable.

Being power driven the equipment is very robust and all the selectors are unidirectional in operation. The provision of a sequence switch reduces the number of relays and with its index disc is useful from a maintenance point of view. In addition to the usual facilities, group hunting, information, "call back," tie line, conference, preference, and code calling facilities can be provided.

The system operates on 46 volts.

Last revised: June 18, 2022