a, 1987). distance between the plant and its battery are significant in terms of The requirements for Telecom's Centre Power Supply Interfaces the voltage drop, and the possibility of picking up spurious voltages have been set out in a CEPT Document T/TR02-02 which has as its as a result of induced or radiated interference. objective the use of the same secondary supplies for all telecom- The large centralised plants with ratings of hundreds or even munications equipment, the harmonisation of the latter, together thousands of amperes, are often interconnected with their associated with the power supply interfaces, maintenance, installation, safety batteries, and the load centres, by copper or aluminium busbar. and operation standards. There are also follow-up proposals by the Because of the lower conductivity of the latter material, a cost European Telecommunications Standards Institute ETSI/TC (89) analysis to trade off the resulting increased physical size is desir- which are currently being considered. 24/14 Telecommunication power systems Power for computer systems financial management information covering the whole life costs of a given installation (Stephenson, 1985). For a large system, the Modern communications networks almost inevitably have associ- annual cost of energy in all its forms may well amount to half the ated computer systems which are likely to work both on and off line total expenditure for telecommunications and building services, (Howard, 1990). All too often they are designed to be operated from whilst labour may account for a further 25% of the expenditure. To a.c. supplies, sometimes even connected to raw supply authority this will have to be added provision for factors such as plant mains. In consequence, such systems become vulnerable to tran- replacement, perhaps some 10% to 15%, the price of training, stores sient interference due to disturbances incoming from the supply and transport etc. making up the remainder. network, and of course, mains breaks both short and long term. For He