The passivation layer is not an insulating layer. It's a bad conductor, almost a semiconductor.
The passivation layer is the part that is passivated. Passivation is the method of transforming the metal surface into a state that is not easy to be oxidized, and delaying the corrosion rate of the metal. In addition, an active metal or alloy, in which the chemical activity is greatly reduced, and become a precious metal state phenomenon, also called passivation.
The mechanism of passivation can be explained by the film theory, that is, passivation is due to the interaction between metal and oxidizing substances, which generates a very thin, dense, good covering performance, and firmly adsorbed passivation film on the metal surface. This film exists as an independent phase, usually a compound of oxidized metals. It plays the role of completely separating the metal from the corrosive medium, preventing the metal from contacting the corrosive medium, so that the metal basically stops dissolving and forming a blunt state to achieve the role of anti-corrosion.
The insulating layer refers to the insulating material layer between the heating wire or between the heating wire and the grounding shielding layer. It is mainly used to isolate power lines to prevent people from getting electrocuted.