19-09-2017, 03:05 PM
An electrical contact is an electrical circuit component found in electrical switches, relays, connectors and circuit breakers. Each contact is a piece of electrically conductive material, usually metal. When a pair of contacts are touched, an electric current with a certain contact resistance can pass, depending on the surface structure, surface chemistry and contact time; when the torque is separated by an insulating space, then the torque does not pass a current. When the contacts touch, the switch is "closed"; when the contacts are separated, the switch is "open". The separation should be an insulating medium such as air, vacuum, oil, SF6 or other electrically insulating fluid. The contacts can be operated by humans in pushbuttons and switches, by mechanical pressure in sensors or machine cams, and electro-mechanically in relays. The surfaces where the contacts are touched are usually composed of metals such as silver or gold alloys that have high electrical conductivity, wear resistance, oxidation resistance and other properties. Beyond the contact surface and the immediate area, the electrical contact is usually composed of other metals for mechanics and cost reasons.