Electric Contact

electric contact

[i¦lek·trik ′kän‚takt]
(electricity)
A physical contact that permits current flow between conducting parts. Also known as contact.

Contact, Electric

 

an electrically conductive surface of contiguous components in an electric circuit or a device providing such contiguity. A distinction is made among electric contacts between current conductors (mechanical contacts), between a conductor and a semiconductor, and between two semiconductors.

Four states are distinguished in the operation of mechanical contacts: open, closing, closed, and opening. Particularly heavy wear occurs in a movable contact during the opening of an electric circuit carrying a large current, since in this case an electric arc is formed. The temperature of such an arc causes melting and partial evaporation of the material of the contact, changing the contact surface. To reduce this undesirable phenomenon, the electric circuit is broken simultaneously in several places or arc-extinguishing devices are used. Materials used for electric contacts include pure metals (platinum, silver, tungsten, rhodium, and copper), alloys (platinum-iridium, palladium-copper, and gold-nickel), and metal compositions (silver-cadmium oxide and silver-graphite); the choice of material depends on the purpose of the contact and on its operating conditions. To im-prove an electric contact a device (or the part of a device where the contact is located) can be placed in a flask containing hydrogen or nitrogen or in an evacuated flask. In such devices the electric contact is operated mechanically (through a corrugated tube) or by means of a magnetic field.

Mechanical electrical contacts are divided into two groups: fixed contacts (split and solid), for a permanent connection, and movable contacts, which are closed only for a certain period of time. Split electric contacts are made by clamps, bolts, or screws; solid contacts are made by soldering, welding, or riveting. Movable contacts, in turn, may be subdivided into break contacts (in push buttons, switches, and relays), sliding contacts (a commutator-and-brush array in a generator), and rolling contacts (the connection between overhead wires and the trolley of a trolleybus). Mechanically operated contacts are used in radio, telephone, and telegraph apparatus, in electric power supply systems, and in precision instruments.

REFERENCES

Spravochnik po elektrotekhnicheskim materialam, vol. 2. Moscow-Leningrad, 1960.
Holm, R. Elektricheskie kontakty. Moscow, 1961. (Translated from English.)

V. I. BARANOV

References in periodicals archive ?
Request for quotations : purchase of electric contact radial pressure gauges for the construction of the facility: modernization of the boiler house of the 18th quarter in the town of dobrush .
A copper wire was soldered to the back of each sample using aluminium solder, and a glass tube covered that wire in order to ensure the electric contact. The samples were mounted in epoxy resin after soldering.
Makkah, Jumada I 20, 1439,February 06, 2018,SPA -- Civil Defense Forces controlled a fire broken out in a hotel at Kaaba mountain in Makkah today due to an electric contact in a utility room in the 22nd floor of the 25-storey building.
Electric contact sensors for joint tracking and/or work piece measurement are representing one type of tactile sensors.
where [[rho].sub.c] and [l.sub.c] are the electric contact resistivity and characteristic length, respectively.
investigated the thermostressed state of coating formation at electric contact surfacing of "shaft" type parts.
This paper deals with the identification of thermal resistances, heat capacity parameters, and electric contact resistances (ECR) at the battery poles of the thermal model.
But it does not occur from an electric contact in such a short time.
When this button is pressed with a finger, it triggers the closure of the spring device of the corresponding terminal, safely and reliably connecting the conductor to its respective electric contact in the connector.
The roots of the CNTs are deeply embedded in the supporting metal matrix, which induces strong mechanical connection and low electric contact resistance.
According to investigations by General Headquarters of Civil Defense, UAE, two major causes of fire are electric contact and sources of combustion.
"We don't want an investigation, result of which would be a story about the existence of an "electric contact," as stated in similar cases in the past, "but strive to know the truth and the real reason behind the fire, to know whether it had been intentional or accidental," she said.