Large-length single core underwater cable must pay attention to whether the protective layer overvoltage will exceed the insulation level of polyethylene anticorrosion sheath.

In order to avoid the excessive protective layer overvoltage caused by the lead sheath and the breakdown of the polyethylene anti-corrosion sheath, the lead sheath and the metal reinforcing zone must be grounded at a certain distance. The design of grounding point and the calculation of the distance between different points must be based on the specific conditions of the cable. In order to ensure the water seal of the place, grounding work is usually done in the factory. The site is generally designed to be located in the factory soft joints.

Some foreign products using semiconductor electric polyethylene sheath, so as to avoid the fixed point grounding of the trouble. The soft joint of underwater cable factory is a major characteristic of underwater cable line. The structural size of the factory's soft joints is the same as or slightly larger than the cable body, and it is as soft as all the linked cables and can withstand the effects of mechanical stresses such as tensile, twisting and bending. Therefore, the factory soft joints in the structure and performance and common joints are very different from the cable body is very similar.