After a heavy rain, a critical power supply circuit in a city’s subway system failed. Upon inspecting the cable, significant water tree structures were observed in the XLPE insulation, and corrosion was visible on the copper conductor surface. Moisture had entered the cable through the terminations, joints, or damaged sheath, resulting in insulation degradation and conductor corrosion, severely affecting the long-term reliability of the cable.
Water Ingress
Moisture can penetrate the cable through poorly sealed terminations or joints, mechanical damage or aging cracks in the sheath material, high hygroscopicity of non-water-blocking insulation or sheath materials, and residual moisture inside insulation or shielding layers from the manufacturing process. For medium- and high-voltage cables, water ingress leads to water tree formation within the XLPE insulation, which can develop into electrical trees under high electric fields, ultimately causing insulation breakdown. Moisture can also corrode copper or aluminum conductors, increase contact resistance, cause localized overheating, reduce insulation resistance, increase leakage current, trigger grounding faults in severe cases, and accelerate the aging of insulation and sheath materials, shortening the cable’s service life.
Moisture Protection System
Modern medium- and low-voltage cables rely on high-performance cable materials to form radial and longitudinal water-blocking systems. Radial water blocking uses lead sheaths, welded corrugated aluminum sheaths, copper sheaths, or aluminum-plastic composite tape (AL/PET) with PE outer sheath structures, providing mechanical protection and radial moisture resistance. Longitudinal water blocking employs water-swellable tapes, water-blocking yarns and pastes wrapped around the cable cores, and superabsorbent polymer (SAP)-based water-blocking powders or tapes placed between conductors and cable cores. These materials expand upon contact with water to form a physical barrier, effectively preventing moisture migration and providing secondary protection for XLPE insulation and LSZH sheath materials.
Moisture-Resistant Cable Structure
A typical medium-voltage water-blocking cable includes copper or aluminum stranded conductors, semiconductive extruded shielding layers, XLPE insulation, a longitudinal water-blocking layer (water-blocking tape/yarn before the metal screen), a metal screen, welded aluminum-plastic composite tape as the outer sheath, and HDPE or flame-retardant polyolefin sheath materials. This structure provides a complete radial and longitudinal moisture protection system. The stability and performance of each cable material directly determine the safety and service life of the cable in complex environments.
Installation and Maintenance
Effective moisture protection also depends on proper installation and maintenance. Terminations and joints must use compatible, high-quality sealing materials such as heat-shrink, cold-shrink, or epoxy sealants to ensure reliable sealing. During installation, the sheath should be protected from mechanical damage, and external forces should be avoided during operation. Regular insulation resistance measurements are essential to monitor moisture conditions in XLPE insulation and LSZH sheath materials. Modern cable systems may also incorporate sheath current monitoring devices to provide real-time warnings of moisture ingress.
High-performance water-blocking tapes, water-blocking yarns/pastes, high-quality sheath materials, reasonable structural design, and standardized installation are key to ensuring long-term cable reliability. As a professional cable material supplier, ONE WORLD provides high-quality XLPE insulation, LSZH sheath materials, water-blocking tapes, water-blocking yarns/pastes, and aluminum-plastic composite tapes, widely applied in power cables, communication cables, and medium- and low-voltage water-blocking cables, helping customers enhance cable moisture resistance and long-term reliability.
Post time: Feb-28-2026