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In this paper a novel insulated cooling system is presented. The work tackles the problem of the cooling of electrical components at different voltage levels by means of the same cooling loop. The system guarantees high thermal performances and electrical insulation enabling a safe and reliable operation of the electrical device. The thermal circuit is based on a two-phase thermosyphon system. The evaporator is made of a round copper tube connected to a natural convection condenser. A common evaporator body provides the cooling of three electric components at different electrical potentials. The condenser is a finned tube type and during operation it is electrically earthed. The evaporator's diameter is 25.4 mm. The electrically dissipating elements are three copper blocks 80 mm wide, equally spaced over the evaporator's length. The total power ranges between 100 and 400 W. The system works with gravity driven circulation. The employed fluid is refrigerant R245fa. The electrical insulation is achieved through elements working as interface between each electrical dissipating component and the evaporator. For good cooling efficiency of the system these elements, in addition to the electrical insulation, must have a good thermal conductivity. Different insulation materials are analyzed and presented: thermally conductive polymers in form of shells interposed between the evaporator body and the heat sources. Thermal performances of the described cooler range between 1 to 3 K/W. A comparison of different interface materials will be given: thermally conductive polymers and the system without electrical insulation added for the reference reasons. Several different thermally conductive polymer grades available on the market are part of the investigation.