An innovative ceramic insulation has been developed by CEA Saclay for Nb3Sn cables. As the ceramic cures during the heat treatment of the Nb3Sn, there is no need for an impregnation afterwards. This process eliminates the epoxy-impregnation steps which present the risk to damage the conductor. The porosity of this insulation is expected to increase the capacity of the heat extraction needed by the next magnets generation. However, in high field magnets, the transverse compressive stress on the cables can exceed 150 MPa, due to Lorentz forces. The effects of this high compressive stress on the critical current of Nb3Sn conductors has been investigated at CEA Saclay in collaboration with CERN using two experimental setups. This paper reports the first quench data measured on ceramic-insulated cables. The samples are compared to a witness sample in order to compute the degradation. It finally appears that the ceramic insulation gives a weaker mechanical support than epoxy-impregnation, leading to an additional degradation of the conductor. Some solutions are proposed to improve the mechanical strength of the ceramic.