Abstract: A contact maker-breaker is disclosed in which the power contacts are associated in series with a superconducting element which is controlled by a heating element and which is structured so as to have a very high resistance following its controlled transition from the superconducting state to the normal state in response to a closing or opening order or following its intrinsic transition from the superconducting state to the normal state in response to a fault current, so that closing and opening of the power contacts takes place on the same leak current of a very low value.

Abstract: The method concerns preparing a contact material constituted by silver and tin oxide.According to the invention the method comprises the following steps:preparing an aqueous solution containing dissolved silver nitrate and tin oxide particles in suspension, with the size of said particles measured in terms of specific surface area using the BET method lying between about 2 m.sup.2 /g and 6 m.sup.2 /g;causing silver nitrate to precipitate in silver hydroxide by rapidly adding a strong base and stirring, with silver hydroxide being unstable and transforming progressively into silver oxide;eliminating the ions from the solution and then the water in order to obtain a dry product; andheating the dry product to a temperature of about 200.degree. C. to 500.degree. C. in order to reduce the silver oxide to metallic silver.The invention is applicable to manufacturing electrical contacts for opening and closing in electromechanical apparatuses.

Abstract: An electric switching unit for preventing oxidation of copper-base contacts in contactors comprises a body (2), comprises an electromagnet (11) having a stationary yoke (7) and a moving armature (15) in cooperating relation with a plurality of switches (36). A protective casing (42) is fixed on the body so as to contain the switches. The contact-studs (30, 31, 32, 33) of the switches (36) essentially have a base of cuprous materials while a non-oxidizing atmosphere is confined and maintained beneath the protective casing (42) by seals (55, 23, 47). The seals are placed on the one hand between the moving armature (15) and a first face (21) of the body (2) and on the other hand between the casing (42) and a second face (41) of the body which is opposite to the first face.