The direct cause of cable NMD90 failure is insulation degradation and breakdown. There are many factors that can cause a decrease in insulation of NMD90 wire. Based on actual operating experience, they can be summarized as follows:
1. Damage during installation, direct external force damage, indirect external force damage, damage caused by natural phenomena
2. The insulation of NMD90 cable malfunctioned due to moisture. The main reasons for cable moisture are: water ingress caused by unsealed or poorly installed joint or terminal box structures; The manufacturing of NMD90 cable is defective, for example, the grounding wire of 14 2 NMD90 cable, 8 3 NMD90 cable, 6 3 NMD90 cable has penetrated other internal wires, and the sheath of NMD90 wire has been punctured or corroded by external objects.
3. Under the action of an electric field, the air gap inside the insulation medium of the NMD 90 wire cable, which has aged and deteriorated, becomes free, leading to a decrease in insulation. When the insulating medium ionizes, chemical compounds such as ozone and nitric acid are generated in the air gap, which corrode the insulation; The moisture in the insulation causes hydrolysis of the insulation fibers, resulting in a decrease in insulation.
4. The design and manufacturing process of the NMD90 cable are poor, and the material selection is improper. Whether it is the 14 2 NMD90 wire or the 3 3 NMD90 stranded copper wire, the materials are all insulated flame-retardant PVC and nylon sheath materials. Poor manufacturing process and failure to produce according to regulations can cause cable head failures.
5. The corrosion of the protective layer of NMD90 Romex wire is caused by underground acid-base corrosion and stray currents, resulting in pitting, cracking, or perforation of the cable lead sheath, causing faults.
