The invention relates to a switch for electrical installations, formed by a casing made from electrically insulating material made up of a hollow body (1) which is closed with a lid (2), internally housing terminals (4) for connecting external cables and an operating mechanism formed by a rocker (6) which is actuated from outside the lid (2) by means of a rocker element (9), the rocker (6) of the operating mechanism being arranged above the position of the terminals (4), such that the latter are close to each other; while the lid (2) is fixed with respect to the body (1) by means of ultrasonic welding joints (12) forming a non-disassemblable compact unit.