CMS Preshower (ES) : proposal for Protective Earthing of the subdetector and of its Silicon bias supply system

There are no good arguments to apply for a derogatory "IT" (Isolé/Terre) earthing scheme for the Preshower, and thus, an appropriate earthing of on-detector active parts is discussed. Complication comes from the absence of a strong DC link between the modules' grounds and the structure, and the safety tying must be obstructed. Fortunately, the bias system is the only Low Voltage supplying system, the other powering is Extra-Low Voltage. The bias supplies have a (very) limited maximum current, and the proposed obstructed tying can even deal with the most extreme type of insulation fault. (Initial electrical safety clearance was based upon elements from this Note.)