Explain the working of thousand line exchanges by using a combination of uniselectors and two motion selectors.

The schematic diagram for such an exchange is demonstrated in Fig. All subscribers is connected to a single rotary pre-selector switch at the exchange, and the outputs from  this switch being linked to a bank of two-motion switches termed as 'group selectors'. The outputs from the pre-selector switches of an entire group of subscribers are connected together in parallel such as group of subscribers share a single bank of group selectors. If a subscriber lifts his telephone then the cradle switch causes a circuit to be completed reverse to the telephone exchange, signaling which the subscriber wants to make a call. It is causes the pre-selector switch to step around till it find a free group selector. The pre-selector switch then stops in such position and the group selector are 'seized' through the subscriber wishing to make a call.

FIG - 1000 Line Exchange

In 1000 line exchange, all subscribers have a 3 digit identification number starting from 000 to 999. By seizing the group selector, the subscriber dials his first digit and the selector switch moves up to the suitable row on the switch contact array. All final selectors have the possibility of connection to 100 lines. Therefore the 1000 lines are divided in 10 groups of 100 each, the group being specified by the first digit in the subscriber's number. Therefore the vertical motion of the group selector selects a last selector in the group related with the first digit dialed. Each single row of contacts or levels, of the group selector is associated to a bank of last selectors associated with a particular group of 100 line numbers. Containing dialed the first digit to select the suitable group, the group selector arm after that automatically rotates in the vertical direction till it finds a free last selector. In the final selector, both directions of motion are in the control of the subscriber's dial and after dialing two additional digits, connection is established, giving the called subscriber's to answer his telephone.