State of the Technique The electric current distribution systems using the bus-bars for lighting systems comprise electrical conductors enclosed in an insulating sheath and housed in a frame or profile equipped both with means for connecting to other similar elements and means for laying. Usually, in order to tap current from said conductors at the user points along at least one wall of the bus-bar profile there are one or more indents or windows, and in line with each of these there is a connector block or socket, which is accessible from the outside. The latter has alveoli to receive the round or flat coupling pins of an electric plug, which must come into contact with the corresponding bare parts of the electric conductors passing in the bus-bar profile.

The connector block or socket can be a known one or preferably the type described in another application for patent by the same applicant. At least one cable is connected to the electric plug to carry the electric current from the user socket.

At present there are various known electric plug combinations made up of two shells between which are positioned the terminals or flexible contacts to

which the conductors are connected, but none which can be closed and blocked without the use of screws or other extra means of attaching.

Objects and Summary of the Invention It is however an objec of this invention to propose and provide an electric plug for the above use which can be easily closed contemporaneously with a respective connector block or socket, without the need either for screws or tools.

A further object of the invention is to provide an electric plug which can be coupled, closed and stably fixed to a respective connector block or socket in a single, simple and easy to perform by a manual movement.

Another object of the invention is to provide an electric plug with a closing and facilitated reversible attachment system, but only intentionally, to a connector block or socket.

These objects and implicit advantages deriving from them are achieved, according to the invention, with an electric plug which includes a body composed of base shell and a cover, where the base shell contains terminals or flexible contacts for connecting the terminals of electric conductors and round or flat coupling pins to an electric plug and wherein: the cover is associated with the base shell and movable between an open and a completely closed position, passing through an intermediate partially closed one, the base shell is equipped with blocking means for engaging with the connecting means of the electric socket when the plug and socket are joined, and

the cover has blocking tangs to interact with, and hold, the locking means of the base shell engaged with said connecting means of the electric socket when the cover is in the fully closed position.

Brief Description of Drawings The invention will however be described in more detail in the description that follows made with reference to the attached drawings, which are indicative and not limiting, in which: Fig. 1 is a front view of the socket, from the round and flat coupling pins side; Fig. 2 is a view of an example of an electric connector block or socket which the plug in Fig. 1 can connect up to; Fig. 3 is a lateral elevation view of the plug ; Figs. 5 and 5 are views from the two opposite ends of the plug ; Fig. 6 is an overhead view of the inside of the base shell ; Fig. 7 is a cross section in the direction of arrows A-A in Fig. 6 and Figs 8 and 9 show, respectively, the cross sections in the direction of arrows D-D and E-E in Fig. 6.

Detailed Description of the Invention The electric socket under examination includes a body 11 and it can be connected and attached to an electric connector block or socket 12 as illustrated in Fig. 2, for example.

The body 11 of the socket is made up of a base shell 13 and of a complementary cover 14.

The base shell 13 has a back wall 13'where, in corresponding housings 15, are assembled the terminals and/or flexible contacts 16 for

receiving the heads of the phase and earth conductors of an electric cable- not shown-with associated round or flat connector pins 17, projecting from said back wall 13'and destined to be received by the corresponding cells 18 in the electric connector block or socket 12. The base shell 13 also has, at one end, an opening 19 for the passage of an electric cable and, on the inside, means for blocking the cable 20. Seals can be positioned on the external and internal faces of the back wall id required.

The cover 14 is associated with the base shell 13 so as to be able to be turned to a raised open position and to a lowered closed position of the socket body. More precisely, the cover 14 is hinged on one side, at 21, to one end of the base shell 13, the one opposite the one with the opening 19 passage for the electric cable, whereas on the opposite side there is a flexible closing hook 22 which engages with a locking bar 23, solid with the base shell 13 to block the cover in its closed position.

The base shell 13 is equipped in an intermediate part, with a couple of flexible locking hooks 24 which project from the back wall 13'each of which ends in an engaging lug 25 on its internal side and a thicker section or cam 26 on its external side.

The electric socket 12 has two housings 27 to receive the locking hooks 24 and in each of these housings an anchor plate 28 destined to engage with the lug 25 of the locking hook.

For its part, the cover 14 has a pair of locking tongues 29 on a level with the hooks 24 of the base shell 13 and a pair of flexible locking hooks 30, facing towards the base shell 13, each one having on its external side a stop

lug 31 which interacts with a facing blocking undercut 32 shaped in the base shell 13.

With the plug 11 disconnected from the electric socket 12 and the cover 14 completely open, the locking hooks 30 of the latter are disengaged and distant from the respective stop undercuts 32 in the base shell 13 and the locking tongues 29 distant from the locking hooks. Consequently, the inside of the plug is fully accessible to connect up the electric cable and/or carry out any other operation which may be needed.

Then, the cover 14 may be turned and closed on the base shell 13; first only partially until the teeth 31 of the locking hooks click over the respective stop undercuts 32 and the locking tongues 29 are made to approach the locking hooks 24; at a later stage they will engage with the locking hooks 24; With the cover partially closed, the plug can be handled in safety in that the internal electric parts are still inaccessible, and connected to the electric socket 12 fully inserting the round or flat contact pins into their respective alveoli. At the same time, the locking hooks 24 of the base shell 13 enter their respective housings 27 in the electric socket, with the lugs of the hooks 25 reaching the anchor plate 28 in said housings. By adding pressure, the cover is therefore completely closed by making its closing hook click over the locking bar 23. With the cover completely closed the locking tongues 29 move alongside their respective locking hooks 24 and, interacting with the external thicker section 26 of the latter, causing the lugs 25 of said locking hooks 24 to engage with their respective anchor plate 28.

Basically, in a single manual action and without abandoning the grip the plug is connected to the electric socket, the complete closure of the plug and

permanent connection of the latter to the electric socket by means of locking hooks 24. Then, as long as the cover remains completely closed, the locking tongues 29 maintain the locking hooks 24 engaged to their respective anchor plate 28 preventing accidental or unintentional opening of the plug and therefore disconnection of the latter from the electric socket. Disconnection of the plug from the electric socket can in fact only be carried out intentionally, by partially opening the cover, limited by its locking hooks 30 engaging the stop undercuts 32, which corresponds to a moving away of the locking tongues 29 from the locking hooks 24 so that the latter may disengage from their respective anchor plate 28, thus enabling the plug to be disconnected from the electric socket.