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Wire and cable knowledge quiz

Update:2020-07-31
Abstract:

1. What are the types of commonly used wires and cables […]

1. What are the types of commonly used wires and cables according to their purpose?
Answer: According to the purpose, it can be divided into bare wires, insulated wires, heat-resistant wires, shielded wires, power cables, control cables, communication cables, radio frequency cables, etc.
2. What kinds of insulated wires are there?
Answer: There are the following types of commonly used insulated wires: PVC insulated wires, PVC insulated cords, nitrile and polyvinyl chloride compound insulated cords, rubber insulated wires, direct buried aluminum core plastic insulated wires for agricultural use, and rubber insulated cotton yarn Textile cords, PVC insulated nylon sheathed wires, PVC insulated cords for power and lighting, etc.
3. What kind of occasion is the cable tray suitable for?
Answer: The cable tray is suitable for laying power cables and control cables indoors and outdoors in general industrial and mining enterprises, and can also be used for indoor and outdoor installations in telecommunications, radio and television departments.


4. What are the cable accessories?
Answer: Commonly used electrical accessories include cable terminal junction box, cable intermediate junction box, connection tube and terminal block, steel plate junction box, cable tray, etc.
5. What is the cable middle connector?
Answer: The device that connects the cable and the cable's conductor, insulation shielding layer and maintenance layer to connect the cable line is called the cable intermediate joint.
6. What is electrical main wiring?
Answer: The electrical main wiring is the connection method of the main electrical equipment and the bus in the power plant and substation, including the connection method of the main bus and the auxiliary power system according to certain functional requirements.
7. What rules should be followed when choosing the cross-section of the power cable?
Answer: The selection of power cables should follow the following principles:
(1) The rated voltage of the cable should be greater than or equal to the rated voltage of the power supply system at the installation point;
(2) The continuous allowable current of the cable should be equal to or greater than the maximum continuous current of the power supply load;
(3) The cross-section of the core must meet the requirements of stability when the power supply system is short-circuited;
(4) Check whether the voltage drop meets the requirements according to the cable length;
(5) The minimum short-circuit current at the end of the line should enable the maintenance device to operate reliably.
8. What are the advantages of XLPE cables and oil-paper cables?
Answer: (1) Easy to install, because it allows a small minimum bending radius and light weight;
(2) Not restricted by line drop;
(3) Good thermal performance, high allowable working temperature and large transmission capacity;
(4) Cable accessories are simple, all of which are dry structure;
(5) Simple operation and maintenance, no oil leakage problem;
(6) The price is lower;
(7) High reliability and low failure rate;
(8) The manufacturing process is few, the process is simple, and the economic benefit is remarkable.
9. What are the requirements for the clamp for the fixed communication single-core cable? why?
Answer: The clamp should have no iron to form a closed magnetic circuit. This is because when the cable core passes current, magnetic lines of force are generated around it. The magnetic line of force is proportional to the current passing through the core. If iron and other magnetic materials are used, Electromagnetic induction knows that eddy currents will occur in the iron to heat the cable and even burn the cable. Therefore, iron pieces cannot be used as fixing fixtures for single-core communication cables.
10. What are the biggest features and advantages of the following heat shrinkable cable head accessories?
Answer: The biggest feature of heat-shrinkable accessories is the use of stress tubes instead of traditional stress cones. It not only simplifies the construction process, but also reduces the size of the joint terminal, which is convenient to install, save time and labor, has superior performance and saves metal. The heat-shrinkable cable accessory integrates the perfusion type and the dry pack type into one, which combines the advantages of these two accessories.
11. What inspection work should be carried out before cable laying?
Answer: (1) The bracket should be complete and paint complete.
(2) The cable type, voltage and specification are designed to fit.
(3) The cable insulation is good. When there is doubt about the sealing of the oil-paper cable, the damp judgment should be made; the direct-buried cable and the small-bottom cable should pass the DC withstand voltage test; the oil sample of the oil-filled cable should pass the test.
(4) The oil pressure of the oil-filled cable should not be lower than 1.47MPa.
12. When in doubt about the sealing of oil-paper insulated power cables, how to use a simpler method to check whether the cable insulation paper is damp?
Answer: Ignite the cable insulation paper or put it in the cable oil at about 150℃ to check, there is no "hissing" or white foam, indicating that it is not damp.
13. What should be indicated on the cable sign? What are the requirements for writing?
Answer: The cable circuit design number, cable model, specification and starting point should be indicated on the sign, and the cables used in parallel should have a sequence number. The handwriting is required to be clear and not easy to fall off.
14. Where should the azimuth signs of directly buried cables be set?
Answer: At both ends of the cable, the cable connector is at 50~100m in the straight section of the cable and the corner where the cable changes direction.
15. For the yellow wax ribbon, black glass lacquer tape, alkali-free glass ribbon, etc. used in the manufacture of cable joints, how to remove moisture before construction?
Answer: (1) Constant temperature drying method: roll the insulating tape into a small roll with a diameter of 25~30mm, put it in a 110~120℃ constant temperature drying oven for 4~5h, cool and dry it out, and put it into a dry sealed cylinder.
(2) Oil immersion and moisture removal method: Put the small coil of insulating tape into the cable oil at a constant temperature of 120~130℃, keep a distance of 30mm from the bottom of the pot, after a certain period of time, the oil surface will no longer generate foam, then take it out and put it into storage In the barrel with cable oil, the oil level should exceed all the contents and seal it.
16. What is the effect of the cable outer sheath?
Answer: Maintain the inner protective layer from mechanical damage and chemical corrosion, and enhance the mechanical strength.
17. What requirements should the outdoor cable trench meet?
Answer: The upper part of the cable trench should be slightly higher than the ground, covered with a cover made of concrete, and the cable should be laid flat on the bracket with a good drainage pipe.
18. What is the effect of the cable inner sheath?
Answer: Keep the insulating layer away from water, air or other objects to avoid moisture and mechanical damage to the insulating layer.
19. What should be paid attention to when using wire cutters?
Answer: Before use, be sure to check whether the insulation of the insulating handle is intact. Do not use wire cutters to cut metal wires that exceed the specifications allowed, and it is forbidden to use wire cutters instead of hammers to hit things to avoid damage.
20. What is dielectric strength?
Answer: Insulating materials will be broken down in an electric field when the electric field strength increases to a certain limit. This electric field strength that causes insulation breakdown is called dielectric strength.

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