These types of spring-cage terminal blocks have an electrical conductor strip, usually referred to as a bus bar or current bar, which conducts the current. This bus bar has one or more openings for inserting one or more stripped conductor end pieces. For this purpose, the bus bar is typically made of a sheet metal strip, into which the openings in the form of material passages are punched. The stripped conductor end piece is typically inserted through a housing opening and into the opening in the bus bar formed by the material passage, and is clamped against the edge of the bus bar opening by means of a leg spring.
These types of spring-cage terminal blocks are used, for example, for the so-called direct plug-in or Direct Terminals for Installation (DTI) technology, whereby the configuration and contour of the leg spring allow the electrical conductors to be wired without tools. In a DTI terminal, the spring automatically opens when the conductor end piece is inserted, thus activating the leg spring. For this purpose, for example rigid single-wire conductors or pre-assembled stranded conductors having a wire end ferrule may be used.
EP 1 391 965 B1 describes an electric spring clamp terminal having a quadrilateral material passage which has an aperture collar and is used as a conductor plug-in opening. The inner wall surface of the aperture collar at that location forms a transverse edge which protrudes against the electrical conductor and extends transverse to the conductor plug-in direction, the transverse edge being formed in particular by the lower outer edge of the aperture collar of the material passage. The aim is to thus form a contact point as an intersection point between the electrical conductor and the protruding transverse edge at the inner wall surface of the aperture collar, thus minimizing the contact surface between the electrical conductor and the aperture collar of the material passage to a fairly small, defined contact surface in order to apply a maximum possible contact force. This improves the current conduction and contact security in the clamping site.
Within the scope of the present invention, however, it has been found that in such a terminal, the conductor may twist relatively easily in the clamping site due to the transverse extension of the transverse edge of the material passage, whereby the transverse edge cuts into the conductor end piece with each turning motion. The stability of the conductor end piece may thus be impaired, in particular for thin conductors.
These types of spring-cage terminal blocks typically may be used multiple times, so that the conductor may be plugged in and pulled back out multiple times. In particular, the conductor is moved during each insertion and removal operation, which is typically also accompanied by rotation. However, any other touching or moving of the conductor may also result in twisting, which is the case in particular in control cabinets, in which a large number of such terminals and associated conductors are present, so that any access to any of the spring-cage terminal blocks also frequently results in touching or moving a plurality of the other conductors.
The insertion force required to plug the conductor into the spring clamp terminal through a transverse edge may disadvantageously be increased. In addition, due to the punching process the transverse edge may have a certain roughness, as the result of which the insertion force may be increased even further, and the insertion operation may be rough and jerky. Accordingly, for such spring-cage terminal blocks a basically desired high clamping force is obtained at the cost of a basically undesired high insertion force. This may result in tilting of the conductor during insertion, in particular for thin conductors.