Switchboard base terminal block for connecting electrical wires comprising: - an insulating body formed by a substantially closed-ring frame and configured so as to define at least a top side and a bottom side opposite each other in a vertical direction (Z-Z), and at least two respective flanks opposite each other in a longitudinal direction (X-X); inside the insulating body there being formed at least: - a first pair of seats situated outermost in the longitudinal direction (X-X) towards the flanks and open in a transverse direction (Y-Y) of width of the terminal block, for housing means for retaining electrical wires , and during use communicating with the exterior via a first respective opening extending in the vertical direction (Z-Z) from the top side of the frame ; - a first space bounded in the longitudinal direction (X-X) by respective first partitions extending parallel to the vertical direction (Z-Z) and vertically interrupted along a heightwise section so as to allow insertion, in the transverse direction (Y-Y), of a conductor lamina for restoring the electrical continuity between the electrical wires , - an undercut with base formed in the top side of the terminal block; characterized in that said first space is centred on a central vertical axis (Z-Z) and said first partitions are spaced from each other in the longitudinal direction (X-X) by an amount such as to define a size of the space suitable for housing a screw jumper ; in that said undercut has a first central opening for connecting with the exterior the central space for insertion of the respective screw jumper , and in that it comprises coupling means (19,19a;14c) for coupling with corresponding coupling means (119,119a;224c) of an add-on terminal block for forming a two-tier terminal block in the vertical direction (Z-Z), wherein said coupling means are adapted for a coupling, which is stable and non-decouplable along the vertical direction, with the corresponding coupling means of the add-on terminal block, said coupling means comprising: a pair of teeth situated opposite each other and extending towards the inside of the undercut from the opposite vertical edges of the undercut , each of said teeth forming an L-shaped spaced seat formed in the respective vertical edge , or at least one tooth extending from each first partition of the central first space . - an insulating body formed by a substantially closed-ring frame and configured so as to define at least a top side and a bottom side opposite each other in a vertical direction (Z-Z), and at least two respective flanks opposite each other in a longitudinal direction (X-X); - a first pair of seats situated outermost in the longitudinal direction (X-X) towards the flanks and open in a transverse direction (Y-Y) of width of the terminal block, for housing means for retaining electrical wires , and during use communicating with the exterior via a first respective opening extending in the vertical direction (Z-Z) from the top side of the frame ; - a first space bounded in the longitudinal direction (X-X) by respective first partitions extending parallel to the vertical direction (Z-Z) and vertically interrupted along a heightwise section so as to allow insertion, in the transverse direction (Y-Y), of a conductor lamina for restoring the electrical continuity between the electrical wires , - an undercut with base formed in the top side of the terminal block; a pair of teeth situated opposite each other and extending towards the inside of the undercut from the opposite vertical edges of the undercut , each of said teeth forming an L-shaped spaced seat formed in the respective vertical edge , or at least one tooth extending from each first partition of the central first space . <EOS>