Electrical contact

A electrical contact is a system allowing the passage of a Electric current through two mechanically dissociable elements of circuit. It is one of the principal elements of the components electromechanical S: Contactor, Relay, Interruptory, Circuit breaker. It is also the key of all the systems of Connectique.

The electrical contact is characterized by its resistance of contact, its resistance to the erosion, its resistance to the Oxydation. In order to optimize its characteristics, surfaces intended to provide the function of contact are covered by plating, or comprise an added massive part, of a particular Matériau.

Materials

Gold

  • low and stable resistance of contact
  • high strength to the film formation of surface.
  • intended for circuits dryness or of low power
  • the contacts for high density of gold are expensive and not very resistant to the transfer of matter, in particular for currents higher than the 1/2A
  • not very resistant to joining, welding, deformation and wear mechanics.
  • the alloys with nickel, money, palladium, etc improve its mechanical resistance to the detriment of conductivity. the techniques of deposition under pressure make it possible to use gold alloys in fine layer on materials such as money, palladium, platinum, nickel, allowing performance as well for dry circuits, as for circuits of 2 or 3A.
  • a certain force of opening must be applied to the contacts to counter the problem of joining or welding of the gilded contacts.
  • the contacts plated gold have a better conductivity than the nonplated contacts, such as the money.
  • the contacts plated gold have a weak lifespan with loads which support electric erosion.
  • the contacts plated gold resist the formation of sulfides and oxides during storage or applications requiring few commutations.
  • the contacts plated gold tend to stick.

Palladium/Platinum

  • points high melting and high boiling
  • abstr. with oxidation and the chemical attacks: low and stable resistance of contact
  • cost of high platinum
  • electric conductivity and low thermics
  • creation of insulating polymers in the presence of organic vapors, during the cleaning or an action of contact slipping
  • the pure material is malleable and deformable (possible deformation due to a mechanical wear)
  • alloy with other metals (money, but, nickel, copper, etc): aug. hardness, formation of polymers (money), dimin. conductivity.
  • low conductivity of palladium/platinum: commutation of weak currents (1-2A)
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