Application of Aluminum Channel Conductors for Station Bus [includes discussion]

Aluminum has been used as an electric conductor since the beginning of the electric power industry. Its use as a conductor material has been second to copper because of the lower conductivity and the difficulty encountered in making connections caused by the rapid oxidation of the material when exposed to air. Except in the case of transmission-line conductors, where weight is a major factor, aluminum found its primary use in light mechanical construction. Therefore its sections have been designed for efficiency in structural applications. When aluminum channels first were applied to station bus, the electric conductor grade of aluminum was rolled on the same machines as the structural shapes. Since these channels have not been designed with uniform thickness, the efficiency of space was much poorer with the aluminum than with the copper channels. Since copper in channel and tubular form would have no other application than as electric conductors, these sections have been designed primarily with that application in mind. When aluminum channels are used as electric conductors, thicker sections may be used more efficiently than with copper due to the greater effective depth of penetration in the material of higher resistivity. This allows, in many cases, the substitution of aluminum sections for copper of the same external dimensions for a given current carrying capacity. With the perfection of silver plating processes for aluminum, which give a plating equal to that applied to copper, the demand for application of aluminum is increasing.