In extruded sheath, the protective layer is broken and the water, damp insulation, insulation resistance decreased. When making multi-core cable, even if the insulation package is in good condition, but when twisted into cable insulation wire core, as well as in extruded layer can also occur when the damage of water be affected with damp be affected with damp, so the finished cable pass the withstand voltage test factory.
In the process of buried cable construction, if the cable trench excavation, buried cable, cable intermediate joint and terminal connector, such as nonstandard production is likely to damage the cable sheath and insulation. If the soil moisture or cable conduit water, cable into the water will occur. After insulation be affected with damp be affected with damp, make the surface of the cable insulation resistance is reduced and surface leakage current increase, insulation resistance drops, also can cause the electric field distortion between the conductor and insulation layer. Insulation inside the uneven distribution of electric field, will lead to internal insulation free discharge, even cause cable breakdown. After-sales service practice has proved that more than 95% of buried cable insulation resistance drop accident was caused by improper construction.
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