Problems in Wire and Cable Laying

1. What inspections should be carried out before cable laying?

Answer: ① The bracket should be complete and the paint should be complete. ② The cable model, voltage, and specification comply with the design.  ③ The insulation of the cable is good. When there is any doubt about the sealing of the oil-paper cable, it should be judged that it is affected by moisture; Directly buried cables and small bottom cables shall pass the DC withstand voltage test;  The oil sample of the oil filled cable shall pass the test. ④ The oil pressure of oil filled cables should not be lower than 1.47MPa.

2. When there is doubt about the sealing of oil-paper insulated power cables, how can a simpler method be used to check whether the cable insulation paper is affected by moisture?

Answer: Ignite the cable insulating paper or put it into the cable oil at about 150 ℃ for inspection. There is no "hissing" sound or white foam, indicating that it is not affected with moisture.

3. What should be indicated on the cable signboard? What are the requirements for writing?

Answer: The signboard should indicate the cable line design number, cable model, specification, and starting point. Cables used in parallel should have a sequence number. The handwriting shall be clear and not easy to fall off.

4. Where should the orientation marks for directly buried cables be placed?

Answer: At both ends of the cable, the cable joints are located at 50~100m of the straight section of the cable, and at the corners where the cable changes direction.

5. How to conduct moisture removal treatment for yellow wax ribbon, black glass paint ribbon, alkali free glass ribbon, etc. used for making cable joints before construction?

Answer: ① Constant temperature drying method: Roll the insulating tape into a small roll with a diameter of 25~30mm, place it in a constant temperature drying oven at 110~120 ℃, dry it for 4~5h, take it out, and place it in a dry sealed cylinder.  ② Oil immersed moisture removal method: put a small roll of insulating tape into the cable oil with a constant temperature of 120~130 ℃, keep a distance of 30mm from the bottom of the pot, take it out after a certain period of time when the oil surface no longer produces foam, and put it into the barrel where the cable oil is stored. The oil level should exceed all the loaded objects and seal them.

6. What is the function of the cable outer sheath?

Answer: Protect the inner protective layer from mechanical damage and chemical corrosion, and enhance mechanical strength.

7. What requirements should outdoor cable trenches meet?

Answer: The upper part of the cable trench should be slightly higher than the ground, covered with a cover made of concrete. The cable should be laid flat on the support, with good drainage pipes.

8. What is the role of the cable inner sheath?

Answer:; To prevent the insulation layer from coming into contact with water, air, or other objects, and to prevent moisture and mechanical damage to the insulation layer.

9. What should be paid attention to when using wire cutters?

Answer: Before using, be sure to check whether the insulation of the insulating handle is intact. When using, do not use wire cutters to cut metal wires that exceed the specifications, and do not use wire cutters instead of hammers to strike tools to avoid damage.

10. What is insulation strength?

Answer: In an electric field, insulating materials will be broken down when the electric field strength increases to a certain limit. The electric field strength that causes insulation breakdown is called insulation strength.