Equipment practices in the 7E rotary telephone switching system

The principles of this system were presented in a previous paper (see Abstr. 1957B03763), and this second part covers mainly the redesign of the main distributing frame, bay equipment, grading and typical layouts. The main distributing frame enables all subscribers' line changes to be made without alterations in the switch room; line jack-strip is illustrated and the schematic of connections is given. Line finder, relays and selector bays are described, and the arrangement of apparatus on bays is illustrated. Homogeneous grading is used because the switches have no home positions. Curves are produced for the accessibility and number of outlets required, plotted against the number of splits, for traffic values from 2 to 152 erlangs per group, valid for probability of loss = 0.01. Grading arrangements are illustrated for 4,5 and 6 splits, and 10-contact grouping. Junction diagrams and floor plans are given and discussed for 3 typical exchanges: 10 000-line exchange in a large multi-exchange area, 6000-line rural centre exchange, and 900-line rural end exchange.