The typical application ranges for different contact materials in devices forpower engineering are illustrated in Figs. 6.3 and 6.4. In the lower load rangesmostly silver and fine grain silver (AgNi0.15) are used because of their highelectrical and thermal conductivity. With increasing currents the more arcerosion resistant AgCu alloy materials are used. For the medium current rangeup to 100A Ag/Ni composite materials are advantageous because of their lowerand consistent contact resistance and their favorable re-solidificationproperties. If higher welding and at the same time arc erosion resistance arerequired, such as for example in motor contactors for switching currents up to5,000A, silver – metal oxide materials are superior. In protective switches(mainly circuit breakers) which are required to handle high short circuit energies,asymmetrical contact pairings are used where the fixed contact is made fromAg/C materials and the moving ones consist, depending on the devicecharacteristics, of Cu, Ag/Ni, or Ag/W. For UL rated and certified circuitbreakers (UL = Underwriters Laboratories) which are mainly used in NorthAmerican power distribution networks symmetrical pairings of Ag/W or Ag/WCare the preferred contact materials.

For very high loads in main power switches and power circuit breakers formedium and high voltage power engineering applications the most suitable