A three dimensional structure adapted for housing and operation of low and medium voltage equipment, comprising: a. corner bars which have hollow square cross section with a small longitudinal split and two circular connection anchors placed inside at each end to facilitate fixing the corner bar to a corner block; b. corner block connected to three corner bars having three bulging sides to which corner bars are inserted and fixed by screws inserted through transverse.holes of the circular connection anchors in the corner bars; c. circular connection anchors which reside inside at both ends of cross bars and sub cross bars and have transverse holes and axial holes of which the former are used to fix either ends of the corner bar or sub cross bar to a corner block or extension block respectively; d. cross bars which have hollow rectangular cross section with a small longitudinal split and two circular connection anchors at each end to facilitate fixing the cross bar to a corner bar, another cross bar, sub cross bar or extension block; e. sub cross bars which have a hollow rectangular cross section with a small longitudinal split and a circular connection anchor at each end to facilitate fixing a sub cross bar to a corner bar, a cross bar, another sub.cross bar or extension block; f. extension blocks which have two square bulging sides to which corner.bars can be inserted and fixed to by screwing through transverse holes of the circular connection anchors of the corner bars and g. thin plastic inserts placed in between when connecting either cross bars or sub cross bars to either corner bars or extension blocks and fixed by means of four screws for each connection made by a cross bar and by means of two screws for each connection made by a sub cross bar all connected in such a manner to realize a frame structure extensible in terms of width, height or depth using extension blocks. a. corner bars which have hollow square cross section with a small longitudinal split and two circular connection anchors placed inside at each end to facilitate fixing the corner bar to a corner block; b. corner block connected to three corner bars having three bulging sides to which corner bars are inserted and fixed by screws inserted through transverse.holes of the circular connection anchors in the corner bars; c. circular connection anchors which reside inside at both ends of cross bars and sub cross bars and have transverse holes and axial holes of which the former are used to fix either ends of the corner bar or sub cross bar to a corner block or extension block respectively; d. cross bars which have hollow rectangular cross section with a small longitudinal split and two circular connection anchors at each end to facilitate fixing the cross bar to a corner bar, another cross bar, sub cross bar or extension block; e. sub cross bars which have a hollow rectangular cross section with a small longitudinal split and a circular connection anchor at each end to facilitate fixing a sub cross bar to a corner bar, a cross bar, another sub.cross bar or extension block; f. extension blocks which have two square bulging sides to which corner.bars can be inserted and fixed to by screwing through transverse holes of the circular connection anchors of the corner bars and g. thin plastic inserts placed in between when connecting either cross bars or sub cross bars to either corner bars or extension blocks and fixed by means of four screws for each connection made by a cross bar and by means of two screws for each connection made by a sub cross bar all connected in such a manner to realize a frame structure extensible in terms of width, height or depth using extension blocks.