sealing is assured by circumferential rubber rings 51 or soft rubber sheets 52 under cover element 47 there is provided a printed circuit board 53 onto which all terminals of the socket are soldered and through which further connections are made additional boards are mounted at intervals by means of securing bolts 54 which pass through tubular spacers 55 these boards preferably include a printed circuit board 56 for the logic components flanked by a pair of shielding boards 57 which shield logic board 56 above and below for external shielding the inner wall of housing 40 can be provided with a shielding coating not shown or the molding can be done using an electrically conductive material a further power supply board 58 and a cooling body of the power semiconductors 62 of this power supply are fastened to the heat conductive sheet 45 connected to the radiator plate 44 depending upon the expected environmental influences at the installation site further structural measures can be taken to minimize damage from penetrating moisture for example hygroscopic material can be placed in a chamber of the cover element or a filter or valve for pressure relief can be put in a perforation in radiator plate 44 or a direct membrane can be provided which equalizes pressure by osmosis or a moisture sensor 68 can be provided on circuit board 53 for generating an error signal in the event of wetting or excessive humidity the electrical connections between printed circuit pc boards can be carried out by multi prong connectors as shown at 61 between pc board 53 for distribution terminals and pc board 56 for logic components or flexible conductors can be provided to connect the pc boards fig4.