The word “contact” not only describes the conductive connection of two mechanically separate electrical conductors, but also the conductive parts (contacts) even if they are not touching. Contacts comprise:
- Non switching contacts as in connectors being opened only for sen/ice or installation (e.g. screw connections)
- Sliding contacts
- Plug contacts to carry but not to switch current
- Switching contacts as in relays, contactors and switchgear
Relay contacts are physically separate but switchable electric conductors designed to make an electrical connection, carry the load current, break the circuit and electrically isolate the load from the supply. How well the contact system actually performs is dependant on the suitability of the contact material, the contact arrangement and the mechanical
An ideal relay contact would consist of highly conductive metal with chemically clean surfaces (no oxidation) and a large, wear resistant, effective contact area. Open contacts would ideally have infinite dielectric strength for electrical isolation. Unfortunately, actual relay contacts do not have these characteristics. An optimal contact material with high conductivity, resistance to oxidation or chemical reactions and resistance against wear and thermal influences during switching can only be a compromise.
Design and cost clearly limits parameters such as the size of contact area, contact forces, relay sensitivity, and the need for big contact gaps for high dielectric strength.
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