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For low-voltage contactors properties like small voltage drop at nominal current, small chopping current, small contact losses, high switching capacity etc. are demanded. Different contact materials become to order with a four -or more-parameter diagram, which facilitates the suitable contact material. After that special characteristics of the CuFe-material are discussed and compared with the CuCr-material with regard to the application in low-voltage contactors. Experiences of the practical lifetime at application round off the contribution.

Micro-arcs appear at micro-roughness spots in making and breaking contact. With the help of contact distance measurements, a delay of the making process as well as an acceleration of the breaking process are detected. Both phenomena can be explained as an explosion-like vaporisation of contact material being sometimes initiated by a micro-arc ignition. These effects are the reasons of the contact material losses and the welding behaviour. Above all, the change of the contact surface structure is responsible for the reduction of the contact live expectancy. Experiments using vacuum tube with main contacts were conducted to study the current, voltage and contact surface relationships.

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