nce, key features of the selection of a particular plant design the most part, the interruptions created by such occurrences are SO should include an evaluation of its quality, efficiency, and need for disruptive to operational work, that most operators may well find it maintenance, besides aspects such as ease and speed of installation prudent to provide a standby engine generator back-up to cater for and commissioning, and the cost of the building structure in which breaks of more than a few minutes, (see Section 24.2.3), and it is to be housed. probably a no-break power plant or UPS to cater for incoming The use of maintenance records to evaluate long term perfor- transient interference and breaks (Nightingale, 1985; Henderson, mance can make a significant contribution to the availability of 1986). management information, and the use of computerised records to produce appropriate data has much to commend it in achieving optimum operating efficiency. One such analysis of telecommuni- 24.7 Customer systems cations power plant for instance, showed that major features of design which need to be considered are that common control fea- tures should be avoided, there is a paramount need to maintain high Business users will often have their own communications facility standards of electrical shrouding and insulation, plant alarm sys- ranging from a few lines to quite major switching systems, some- tems must fail safe, power distribution schemes must be capable of times in association with their own computer equipment. Such being safely extended, and that battery interconnections to its asso- systems will merit the same consideration for reserve power plant ciated plant must be designed with the utmost care (Coppinger, as the main network providers, and the power plants available can 1987). be based on the same design criteria as previously outlined. In the case of modern systems of modest capacity it will be found that the power plant will be based on similar ideas to those for main ex- change distributed power plant 