Each element (9) in a flat housing (10) serving for connection has an electrode plate (15) closely spaced with an insulating layer to form a second connection. The elements (9) are connected together electrically by metallisation (23, 24) on a circuit board (21) with a bonding layer (22) pref. of high-m.pt. polyamide resin without pinholes. Conductive parts (34-37) occupying through holes (26-29) in the board (21) connect the electrode plates (15) and portions (11) of the housings (10) to respective metallised connections (23, 24) on its surface. ADVANTAGE - Sealing of each element is achieved with structure which does not add significantly to thickness.