a with modern electronic equipment than the old electro-mechanical long service life, and their condition can be determined by straight- systems. Faults impinging on the distribution, and clearing via the forward visual inspection. protective devices, (or 'burning off'), will cause voltage disturb- Nickel-cadmium cells are also used, particularly where high ca- ances. Transients or 'spikes' SO generated, whilst of very short pacities are not required, in applications such as for UPSs, or engine duration, will often reach two or three times the nominal distribution starting (Feder, 1987). voltage value, and are capable of causing actual damage or at the The more recent development of the valve regulated sealed lead very least the malfunction of connected equipment. Hence it is of battery (Harrison, 1986; Wittey, 1985) whilst not at present able crucial importance that distribution schemes, and the selection of to give the same high levels of capacity of the lead acid cells protective devices, are carefully considered in their basic design, described earlier, now give the opportunity for the integration of the e.g. anti-surge fuses are used where appropriate. cells into the equipment racks. They also have the significant ad- As an alternative to tree and branch types of distribution modern vantage of not requiring the use of purpose built accommodation, equipment schemes may use a radial-cable arrangement, with a and for future U.K. telecommunications systems they are likely to single earthing system (Wilson, 1980). In such a system problems become the dominant type of battery in service. from contacts between different earthed elements tend not to arise For some applications in the future, there is a prospect of a lithium because all parts of a given nominal earthed system are bonded polymer type of battery becoming available. It has been argued that together, (the mains earthing conductors excepted), into a single this design may be regarded as the next logical step ahead from the large system. By design these sy