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Engineering LibreTexts

2.3.2 Contacts

Contacts, meaning mechanical contacts here, are a major part of most electronic products. Even if there is no mechanical switch anymore, you still have the contact between the plug and the outlet, and/or the contact springs for the batteries.

Contacts include the following items:

  • Switches, plugs, relays, connections to removable parts (batteries, light bulbs, ...), pantographs (the thing on top of a locomotive), "brushes" (for motors), and so on.
  • Contacts are also the components or materials that often cause trouble. Contacts or switches are often the first components to break, and thus a nuisance to consumers like you and me.

There are many specific requirements for contact materials:

  • Small contact resistance (it is never zero).
  • No sticking or welding under load.
  • No abrasion under load.
  • No intermixing of materials.
  • No wearing and tearing.
  • Suitable mechanical properties, e.g. good elasticity (forever) for switches.

There are specific materials and group of materials generally favored for contacts:

  • C (graphite in many forms) for pantographs and whenever you want to draw a big current.
  • CuAgAu.
  • RuRhPdOsIrPt.
  • MoW.
  • ....
  • An example of Ag-based contact materials can be found in the link.
  • For contact applications we find expensive materials, because in many applications only small quantities are needed and the inertness of noble metals is what counts.