FR2672723A1 - ELECTRIC CABLE CORD FOR LOW CURRENCIES. - Google Patents

Abstract

The bead is characterized in that its conductor consists of several strands (1) of very small diameter made of an alloy of copper, cadmium and tin, and several strands of very small diameter made of hard tinned copper (2). Application: telephone set cord.

Description

Electric cable cord for low currents

  The present invention relates to an electric cable cord for low currents, in particular for telephone sets.

  The cords of electric cable for low intensities, such as the cords of the telephone set, are in general spiraled They must undergo without degradation of their mechanical characteristics a very large number of operations, implying a stretching of the turns and stresses of traction and bending at the point of their exits from the base and the earpiece of the telephone set These cords are currently formed by an assembly of fine strands of twisted copper, so as to have sufficient electrical conductivity. However, such cords do not exhibit resistance. to completely satisfactory fatigue After a certain period of service their spirals no longer return completely to their initial state, and the cords are sometimes subject to ruptures at the level of their exits from the telephone set, so that the we have increased the diameter or the number of their strands far beyond what would strictly be nt necessary from the point of view of the required electrical conductivity This results in a corresponding increase in their

size and their weight.

  The object of the present invention is to provide an electric cable cord for low currents, which has an improved fatigue resistance compared to that of known cords, and

  diameter, size and low weight, while having sufficient electrical conductivity.

  The electric cable cord according to the invention is characterized in that its conductor consists of several strands of very low

  diameter in alloy of copper, cadmium and tin, and several strands of very small diameter in hard tinned copper.

  The alloy of copper, cadmium and tin is preferably the alloy comprising by weight approximately 98.5% of copper, 1% of cadmium

  and 0.5% tin, sometimes called, moreover improperly, "telephone bronze" This alloy has an electrical conductivity of 85% to 95% of that of pure copper.

  For telephone applications, the diameter of the strands is -2-

of the order of O, lmm.

  The invention is described below by way of example with reference to the single figure of the appended drawing, showing in section a radio telephone cord conductor according to the invention. This conductor is formed by a strand of 4 strands 1 of 0.12 mm in diameter, made of copper-cadmium-tin alloy defined above, and of 3 strands 2 of 0.12 mm in diameter, of hard tinned copper. These strands 1 and 2 are coated with an individual insulating sheath 3 and are covered with an outer protective sheath 4, surrounding

  the assembly This cord conductor has an overall diameter of 4.5 mm.

  A cord comprising this conductor has very good resistance to fatigue tests, both with regard to the elasticity of its turns and its resistance to traction and bending. It advantageously replaces from this point of view a cord with conductor formed from 15 strands of copper and its conductor diameter of 7 mm, and allows a significant reduction in the diameter of the turns, substantially the same

  order than that of the conductor diameters. Its electrical conductivity, although lower than that of the copper stranded conductor, remains satisfactory.

  The insulation of the spiral telephone cord with mixed strand according to the invention was checked by subjecting it to a current of one amp in 4 conductors for 1 hour at 550 C. Measurements under a voltage of volts, after one minute of switching on voltage, enabled the following insulation resistance values to be noted At 200 C, before the test, resistance 7 to 9 106 megohms At 550 C, at the start of the test, 106 megohms After 1 h at 55 "C and 1 amp in 4 wires: 106 megohms After 10 stretches at 550 C: 106 megohms After 12 h at 200 C: 3 to 4 106 megohms

  After 10 stretches at 200 C: 3 to 4,106 megohms.

  These measurements clearly show that the cord can withstand without loss of quality a current of A per wire under a temperature of

550 C.

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Claims (2)

  1 / Cord of electric cable for low currents, in particular for telephone cords, characterized in that its conductor consists of several strands of very small diameter made of copper, cadmium and tin alloy, and of several strands of very small diameter in hard tinned copper.   2 / electrical cable cord according to claim 1, characterized in that the alloy of copper, cadmium and tin comprises by weight   about 98.5% copper, 1% cadmium and 0.5% tin. -