Aluminum bus for shipboard application

THERE is special interest in aluminum for shipboard use because of the savings realized in weight and because of shortages in copper that occur especially in times of national emergency when shipbuilding is at its peak. Although aluminum has been considered for cable conductors for shipboard use it is generally without over-all advantage because the larger conductor size results in a greater volume and weight of insulating and sheathing materials. These factors involving insulation are not imposed in applying aluminum to electrical bus. In utilizing aluminum bus for switchgear application problems arise that are mostly but not entirely confined to the making of satisfactory electric connections. The literature on the subject contains a large body of information. Much effort is devoted to coping with a particular environmental stress or material property considered to predominate in the reliability of a specific system. Some of the work stresses the advantage of a proprietary material or a particular method. Instances of controversy are attributed largely to differences of conditions of evaluation and as such appear best capable of resolution by re-evaluation on the same basis. The rather extreme conditions and their wide variety in shipboard service justify additional evaluation. A comprehensive experimental investigation was therefore carried out to determine the optimum means of utilizing aluminum bus in switchgear with the primary objective of long-term service reliability. Measurements taken on large numbers of specimens determine the extent to which different types of aluminum joined by various bolting methods, and with joint surfaces prepared with various joint compounds, are affected by prolonged load cycling, overload, weathering, vibration, and high impact shock; similarly tested is the extent to which silver platings are affected. Measurements on an actual marine installation after 20 years of service are correlated with the results of experimental laboratory work. In addition, information is provided which is useful in the design of bus supports needed to withstand fault currents.