Abstract: A device for transmitting electrical energy or electrical signals comprises a core, an outer conductor and a threshold characteristic dielectric material between the core and the outer conductor. The dielectric material comprises, at least in part, a material that is insulative if the electric field is below a particular threshold and conductive when the electric field exceeds a particular threshold, so as to prevent the transmission of signals for which the electric field is above the threshold. The configuration of the core and/or of the outer conductor is such that the external electric field threshold from which the material becomes conductive is significantly less than the intrinsic breakdown threshold of the material.