Miniaturized lighting or overload protective device and protective device used therein

#1. Field of the Invention

#The present invention relates to a miniaturized device for connecting electrically conducting elements subjected to very high currents.

#Electrically conducting elements are generally connected by bringing together two conductors subjected to a pressure created by a mechanical system. These conductors are very generally made from copper more rarely from brass or silver. Since these metals are very good conductors of electricity the dimensions of the connecting wires are very small even for very high currents. For example, a hundred amps or so may be carried by a copper wire of a section of 0.1 mm.sup.2 without melting. On the other hand, the connection of such elements involves much greater dimensions of the conductors. In contact with the conductors, the resistivity is very high. That is due to oxides, to surface impurities, to the reduction of the contact area. To obtain a good connection despite this high resistivity, the connecting area is increased and of course the space required as well. These considerations lead to very large dimensions for the connection with respect to the dimensions of the conductor itself. In the case of clamping by screws and binding clips, over identical lengths, the space occupied by the connection is 30 to 100 times greater than the space occupied by the conductors.

#Different embodiments of the present invention will be described hereafter by way of non limitative examples, with reference to the accompanying drawings in which:

#FIG. 1 is a sectional view of a miniaturized connection device between two conducting wires in accordance with the invention;

#FIG. 2 is a longitudinal sectional view of an overvoltage protective device using miniaturized connection devices of the invention.

#The device which is shown in FIG. 1 is intended for the electric connection of two electrically conducting wires 1 and 2, made for example from copper, whose end parts are close to one another, while being for example parallel to each other. These wires are connected electrically by a binder 3, having a low melting point (200.degree. to 300.degree. C.), and electrically conducting, such as a lead-tin alloy and which forms a solid mass at ambient temperature. A rigid coating 4 surrounds the whole of the connection along all the axes.

#When a very high current flows through conductors 1 and 2, the resistivity of binder 3, greater than that of the conducting wires 1 and 2 and the greater resistivity at the surface of the metals means that heat is produced in the zone of binder 3, by Joule effect, in a proportion much greater than in the conductors 1 and 2. Depending on the duration of the very high current, there is partial or total melting of binder 3. This latter maintains the connection even in the liquid state, because of coating 4 which perfectly confines it about conductors 1 and 2. This coating is chosen so as to leave no air bubble between the binder 3 and the coating 4, for the probable movement of the air bubble by gravity during melting of the binder 3 could result in increasing the resistivity, this increase causing an increase in temperature by oxidization of the binder 3 because of the oxygen in the bubble and deterioration of the connection.

#Coating 4 is chosen so as not to have any chemical reactivity with the binder 3. It is also chosen as a function of the foreseeable duration of melting. For example, an epoxy resin may resist for 10 ms at a temperature of 1000.degree. C. and a ceramic for several seconds at the same temperature.