The present invention relates to an insulating element (1) for producing an insulating and supporting device for busbars to install in cabinets for low voltage distribution switchboards. The invention also relates to an insulating and supporting device for busbars comprising the insulating element which essentially comprises a body made of insulating material (5) which extends along a longitudinal axis (100) between two end surfaces (8) transverse to this axis. The body made of insulating material (5) comprises a plurality of lateral surfaces (10, 20) which extend between the end surfaces (8) in the direction of said longitudinal axis (100). At least a first (10) and a second (20) of these lateral surfaces are provided with longitudinal grooves (11, 21) defined between connecting portions (15). In particular, the longitudinal grooves (11) defined on the first lateral surface (10) have a longitudinal extension (L1) differing from that (L2) of the grooves (21) defined on the second lateral surface (20).