h the more modern installa- percent, they will be maintained in a healthy condition with little tions where power plant proper is distributed around a building, and need for boost or refresher charges. Maintenance tends to be at a hence the current values to be carried are well within the capability minimum, and a life of 10 to 20 years is achievable. In the majority of cable conductors. The latter arrangements have, of course, the of capacities in regular use, the Plante' cells tend to be contained in added merit of being generally simpler to install, and have a greater glass boxes, which give the not inconsiderable advantage of allow- degree of flexibility in terms of extending existing plant and equip- ing the condition of the cell plates to be inspected. ment schemes. Additionally, insulated cable conductors are in many There are also pasted positive plate traction cells, and the tubular ways inherently simpler to protect from accidental contact, and element or gauntlet cells. These have the merit of being rather hence have a lower fault liability. smaller in overall size compared with the equivalent Plante', and are Electrical protection of the distribution systems chosen may be by often of a more rugged construction, which in some cases can have means of fuses, or for very large systems, breakers; although inter- considerable merit when used say for mobile units. However, they estingly it has been found by experience that fuses or circuit have some limitations which can give rise to a somewhat lower breakers of about 500 amperes do not often operate, even under degree of reliability, or shorter life, in the applications previously severe fault conditions, the faults sometimes burning clear before described; and certainly organisations such as BT have used the the protective devices have time to operate (Wilson, 1979). Plante' cell as standard because they can be kept in good condition Power supply disturbances are of a more profound significance when maintained by the float trickle charge method, they have 