In principle, it is not allowed to exceed the minimum service temperature of insulating sheath and protective sheath. Because there are many choices for wire and cable specifications and materials used for insulating layer and protective layer, this temperature is actually not fixed and depends on the maximum current carrying capacity of the cable.

For example, the EPDM rubber cladding is at least 70 degrees and 90 degrees, the PVC cladding is at least 65 degrees, the rubber cladding is at least 65 degrees, and the RVV copper-core PVC insulated sheathed flexible cable is 105 degrees and so on. In addition, the insulation and protective layer of existing cables are mostly made of organic polymers, so if the surface temperature reaches 250 degrees, the polymer will age, denature or even break the chain, coke or cause open flame for a long time.