If the thin part of the low-voltage power cable sheath fails to meet the requirements, the cable sheath will be damaged before reaching the normal external destructive force. As the magnesium oxide crystal powder used as the insulator in the low-voltage power cable is a material with high moisture absorption, once the outer sheath is slightly damaged during cable transportation and laying, the magnesium oxide crystal powder will be affected by moisture and the resistance will be greatly reduced. In addition, When making the middle end connector of the cable, the cable shall be cut off, which will also cause the magnesium oxide crystal powder to be affected with moisture.
1. Dehumidification method of cable damping end
At the end of low-voltage power cable, the range of moisture intrusion is generally 300-400mm. However, if the cable end is not temporarily sealed and is exposed to the air for a long time, the moisture can invade about 1m. At this time, the wet end of the cable can be tilted upward, and the cable can be gently baked with a gasoline burner from about 1m away from the cable end, so that the moisture in the magnesium oxide of the cable is gradually discharged from the inside to the outside. If the insulation resistance of one end measured after baking rises slightly, Continue to bake the other end of the cable with the same method until the insulation resistance is qualified.
2. Find and repair the damaged copper sheath of low-voltage power cable
When the copper sheath in the middle part of the cable breaks during construction, the repair method is: after the low-voltage power cable is leveled and dehumidified, the insulation resistance of the insulation layers at both ends does not rise or change little, which can be judged as the fault of the middle part. The whole length of the cable can be baked with slow fire, and the high resistance of the multimeter can be used to search. If the pointer reading changes greatly when baking a part, the fault point can be determined here, and then the power supply system can be cut off, Bake with a slow fire for dehumidification. After dehumidification, check whether the insulation value is qualified. Connect the cable with an intermediate connector. The resistance change curve of the wet cable insulation when baking at 200 ℃, as well as some related issues that should be paid attention to in the selection and use of low-voltage power cables.
Low voltage power cables are used in important buildings, such as high-rise buildings, docks, stations and other key parts, such as fire control, fire pumps, smoke exhaust fans, automatic fire alarm devices and other electrical circuits, which is conducive to reducing project costs and facilitating construction and maintenance. Secondly, the terminal of low-voltage power cables is longer than ordinary cables and is not easy to bend. When laying cables, special tools should be used to cold process the dome to prevent damage to the copper sleeve, Keep the sealant and sealant properly to ensure that the insulation resistance meets the specification requirements.
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