The subject of the invention is an enclosure for secondary distribution modular switchgears, applicable in protecting switchgears both against adverse weather conditions and against unauthorized inspections of high, medium and low voltage switch gear, and also against accidental access by unauthorized persons, or by wild animals and birds.The inventive enclosure containing a base-frame (3) to which the enclosure walls are attached and which is provided with a roof cover is characterized in that the base frame (3) is formed by a metal truss and contains two extreme base-frame modules, the left one (20) and the right one (23,) and at least one middle module (21 and/or (22) which are connected with one another by means of a pair of permanent connections formed by a socket (27a) and a prong (27b) and fastening and earthing plates (28a, 28b).