Abstract: A unitary rectangular junction box module composed of a back rectangular base block molded from non-conductive material and having parallel bus bars laid edgewise in its front face and arranged lengthwise of its opposite side walls, the opposite ends of the bars terminating short of the outer surfaces of its end walls, in combination with a front rectangular block having a centrally disposed rectangular opening extending rearwardly therethrough, the marginal back face of the front block being laminated to the marginal borders of the front face of the back block to thereby lock the opposite ends of each bus bar between the block while leaving the intermediate bar segments accessible through said opening. The opening also may be used to telescopically receive selected unitary plug-in accessory modules for use with the junction box module.