cap 31 further mounted on strip 4 is a connector 32 for suitable realization of the interconnection of the electric wiring from power supply to lamp holder 30 and ballast 5 mounted on the front edge of the base plate 1 are two upright lugs 33 and 34 on which a pressure switch 35 lug 33 and a pull relief 36 lug 34 are mounted at a suitable location on opposite sides of the plate 4 two upright brackets 37 and 38 have been forced out from the base plate 1 intended for mounting the cap construction to be discussed hereinafter the cap 16 referred to is more or less box shaped in the embodiment shown in fig3 provided in the front wall of the box shaped cap 16 is an opening 39 for the operating button of switch 35 to extend through in operation provided further in that wall is a recess 40 which in operation is positioned facing the pull relief 36 so that a flex can be passed therethrough to the base plate 1 provided in the top surface of this cap 16 too an opening is provided having a broader portion 17 and an adjacent narrower portion 18 provided along the long sides of the broader portion 17 of the opening is a support edge 20 while along a part of the support edge 20 a downwardly directed strip 41 42 is mounted provided at the bottom of the strips 41 42 are means of attachment each comprising a fixed block 43 44 and a resilient part 45 46 attached to the fixed block when the cap 16 is being mounted the attachment means.