Materials for light-duty electrical contacts

Abstract

Established materials for light-duty electrical-contact applications are based on the platinum-group metals and gold; silver, copper, tungsten, and their alloys are employed for heavy-duty contacts. The main features of the operation of heavy-duty contacts are arcing and welding, which become important when the power being switched exceeds ∼ 100 W or the current ∼ 1.0 A. In the light-duty field, erosion transfer, mechanical wear, and contact resistance are the phenomena of contact operation that have to be considered. With light-duty contacts, surfaces must be free from tarnish films to ensure low contact resistance: hence the use of the platinum metals and gold. Silver can be used only in restricted light-duty applications where the electrical and mechanical conditions permit rupture of sulphide films.