A switchboard or a display board for an electric monitoring and control system is comprised of at least two modular elements, the modular elements having visible sides of the same regular contour or of a multiple of said regular contour, the visible sides of the modular elements abutting each other to form a continuous pattern constituting a visible side of the switchboard or display board. Each modular element comprises a surface element forming the visible side and side walls projecting backwards from the surface element, the surface element having edge portions projecting outwards of the side wall and forming a peripheral region, the edge portions having outer edges with mating tongue and groove profiles whereby abutting surface elements of the modular elements may be plugged together while leaving gaps between adjacent ones of the side walls below the projecting edge portions, and the side walls being formed with undercut locking grooves. Connecting elements are inserted in the gaps between the adjacent side walls and have detent projections engaging the locking grooves.