installation chamber 41 formed on the outer surface of top part 36 are cooling ribs 38 formed on the outer surface of the bottom part are cooling ribs 39 arranged in installation chamber 41 are the electronic subassemblies in this arrangement a printed circuit card 55 of the power component with a transistor 40 is secured in vibrationproof manner by means of mounting elements 56 directly to the top part 36 whereas a printed circuit card 43 of the control electronic devices is connected to bottom part 37 by means of mounting elements 57 the printed circuit card 55 and the printed circuit card 43 are interconnected via a plug connection 58 to improve the heat transfer between printed circuit card 43 and bottom part 37 the space therebetween may advantageously be filled at least in places with a highly heat conductive material which acts as an electrical insulator since the power semiconductors release a significant portion of the dissipation power of the frequency inverter a temperature gradient develops in the installation chamber 41 thus a temperature of about 130 u00b0 c adjusts itself on the inner side of top part 36 and a temperature of about 70 u00b0 c on the inner side of bottom part 37 to avoid that the temperature on the bottom part is increased in addition by power semiconductors 40 a heat insulation 44 is arranged between top part 36 and bottom part 37 furthermore the cooling surface formed by.