 of system reliability being sought. distribution scheme rapidly becomes unwieldy electrically, and excessively difficult to safely extend without recourse to removing the plant, and the equipment it supplies, from service. Additionally 24.3.3.6 Distributed plant the demands on accommodation to house the plant, and associated maintenance costs become onerous. As a result, in the U.K. during During the 1980s the development of new electronic switching the 1970s (Pine, 1971; Nightingale, 1971) plant and switching equipment and related computer based systems, and the rapidly equipment design philosophies evolved to cope with these prob- emerging additional services associated with communications sys- lems. Firstly there was a design definition that to the maximum items, coupled with the development of a new generation of power possible extent, all connected equipment should be capable of switching devices and sealed secondary battery systems, has led to operating from a nominal -50 volt d.c. supply. a totally new approach to d.c. power equipment (New, 1982; Wittey, The actual power plant design was modular in approach and it is 1983; Owen, 1985; Jacobs, 1984). In a nutshell, power plant has still widely used (Henderson, 1979). In essence the design brief been modularised and miniaturised to the extent that both the power requires power plant to be capable of safe extension SO that it can converter (Spooner, 1986) and its associated batteries can be closely 24/12 Telecommunication power systems Converter Rectifier No.1 Narrow Voltage Limits Rectifier No. 'n' Distribution No Break Supply Inverter Supply Power Management System Alarms Interface Remote Interrogation System Voltage Limits Battery No.1 Distribution Battery No.'n Figure 24.14 Distributed plant. All of this plant can be mounted on a power rack mounted en-suite with the equipment rack associated with the equipment it serves. It has become rack 24.4 Battery systems mounted, purpose built accommodation is no longer needed; and this design arrangement reduces t