This group of Elkonite® materials consists of a series of tungsten-silver compositions with the tungsten content of  78%, 65%, or 50% by weight. Tungsten has the highest strength and highest melting temperature of the refractory metals. This is the principal factor in determining a contact’s resistance to arc erosion and mechanical wear. The strength, erosion and weld resistance characteristics of the contact increase with increasing tungsten content; the electrical and thermal characteristics decrease. In selecting a material composition for a given application you should choose the highest refractory content that will provide a satisfactory temperature rise and current interruption.
These are infiltrated materials with a strong sintered structure. They provide the greatest strength and excellent erosion characteristics for a given weight percentage of refractory metal. These press-sinter-infiltrate materials are used in very large circuit breakers. They are also used in small molded case circuit breakers, and medium duty switching devices.
Elkonite® 20S has a high refractory content and normally the greatest resistance to arc erosion. It is generally used as arcing contacts in large air and oil circuit breakers, line disconnects, reclosures and in high current switches and contactors. Contact resistance is low enough to protect the higher conductivity current carrying contacts from arc damage. Its resistance to welding makes it a good shorting contact for bimetal protection in circuit breakers.
Elkonite® 35S has more silver which provides higher conductivity and a lower contact resistance. They are used extensively in a large variety of circuit breakers. In this application a single pair of contacts provides the dual function of carrying the current without overheating, and interrupting the current without excessive arc erosion. They are also used in high current contactors where resistance to contact welding and arc erosion are required. In a variety of DC applications they offer resistance to metal transfer.
Elkonite® 50S contains still higher contents of silver and is used where higher conductivity and low contact resistance is needed. In some breakers one pole tends to have greater erosion. In these cases Elkonite® 35S can be used on this pole and operated against Elkonite® 50S. Elkonite® 50S has the highest silver content of these materials. It exhibits good resistance to contact welding and is used for current carrying contacts in power circuit breakers that encounter high momentary currents.