In some cases, the power junction box cannot be directly installed on the pipeline or equipment, so the heating cable or temperature sensor signal line needs to pass through the insulation layer to connect to the junction box, and there is a risk of being cut by the outermost metal shell of the insulation material. Therefore, in this case, the relevant insulation layer bushings are prefabricated on the heating cable body, the cold end or other signal lines passing through the outermost metal shell of the insulation material to protect the safety of the line body.