The switching equipment consists of 4000 type two-motion selectors and Type 2 Uniselectors. The trunking arrangements, which are shown on Dgm SA 8540, are essentially similar to those of the PABX 1. The equipment is accommodated in two cabinets, known as Equipment's, PABX 7/1 .... and 7/2.... having capacities of 9 + 50 and 11 + 50 respectively these cannot be extended. The Equipment, PABX 7/1 .... which includes the ringing and tone supplies can itself form a complete PABX but generally the PABX 7 will be supplied only to those subscribers requiring both units. Both equipment cabinets have doors back and front for engineering access. Power is supplied by secondary cells float charged by a rectifier from the mains supply, this is of the type described in Q0070. The layout of the equipment is shown on Drgs CD 2289 and CD 2290. Relay- sets of types not shown on the drawings are fitted in any of the positions allocated to miscellaneous circuits shelf jacks and the necessary wiring is provided on site when required. A single desk-mounted cordless switchboard, known as Switchboard SA 8551 (see picture) is provided with a handset as standard, but a lightweight headset (trimphone style) can be supplied as an alternative. The normal capacity of the PABX is reduced by one exchange line and one automatic extension line for each auto-auto inter-PBX line or manual extension provided, and by one exchange line for each manual-manual inter-PBX line provided.
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