Since the magnesium oxide crystal powder as the insulator in the BTTZ cable is a material with very high moisture absorption rate, once the outer sheath is slightly damaged during the cable transportation and laying process, the magnesium oxide crystal powder will become damp and the resistance will be greatly reduced. ; In addition, the cable should be cut off when making the middle of the cable and the terminal joint, which will also cause the magnesium oxide crystal powder to become damp. In response to these situations, there should be corresponding handling methods on site. There are usually the following two situations:
1) Dehumidification of the damp end of the cable
At the cable end, the moisture intrusion range is generally 300-400 mm, but if the cable end is not temporarily sealed and exposed to the air for a long time, the moisture can enter about 1m. At this time, the damp tail end of the cable can be tilted upward and a gasoline blowtorch can be used from about 1m away from the end of the cable to simmer and dehumidify, so that the moisture in the magnesium oxide of the cable is gradually dissipated from the inside to the outside, and the flame should move slowly during operation. , To achieve uniform heating, pay attention to control the surface temperature of the copper sheath within 200 ℃, and remove the moisture. If the resistance value of the insulation resistance measured after baking at one end does not rise much, use the same method to continue baking the other end of the cable until the insulation resistance value is qualified.
2) Finding and repairing damage to the copper sheath of the cable
When the copper sheath of the middle part of the cable is cracked during construction, the method to find and repair is: first, if the insulation resistance of the cable at both ends of the cable does not increase or change after being tempered and dehumidified, it can be determined as the middle part. For segment faults, you can bake the full length of the cable with a slow fire and use a multimeter to find the high-resistance file. The specific method is: adjust the multimeter to high resistance, connect one end of the meter head to the cable core, and the other end to the outer sheath, use a blowtorch to burn and heat along the cable head, and observe the changes in the pointer readings, if the pointer is baking When the reading changes greatly at a certain part, the fault point can be determined here. After that, cut the cable and dehumidify it with a slow fire. After dehumidification, check whether the insulation value is qualified. After the resistance value is qualified, use the intermediate joint to connect the cable. When dehumidifying, pay attention to the change of heating temperature and resistance value. The resistance change curve of the insulation layer of the damp cable when it is baked at 200 ℃. At the same time, some related issues should be paid attention to in the selection and use of BTTZ cable:
First of all, BTTZ cables should be used in important buildings, such as high-rise buildings, airports, docks, stations, etc., such as electrical appliances such as fire control centers, emergency lighting, fire pumps, backup power supplies, smoke exhaust fans, and automatic fire alarm devices. Loop, which is beneficial to reduce project cost, shorten construction period, and facilitate construction and maintenance. Secondly, the terminal head of the BTTZ cable is longer and difficult to bend than ordinary cables. Therefore, when customizing the distribution box, you should fully consider reserving enough space for operation. When laying cables, special tools should be used to cold work the bends to prevent damage to the copper jacket. The production of terminal heads and intermediate joints should strictly follow the operating procedures to keep the operation site clean and free of impurities from the sealing glue, sealing paste and silica gel, and ensure that the insulation resistance meets the requirements of the specification.