Knowledge that needs to be known in weak current engineering construction
2025-06-04 14:13:20
01. What are the common types of wires and cables classified by their usage?
Answer: Based on their functions, wires and cables can be categorized into bare wires, insulated wires, heat-resistant wires, shielded wires, power cables, control cables, communication cables, radio frequency cables, etc.
02. What types of insulated wires exist?
Answer: There are various types of insulated wires, such as polyvinyl chloride insulated wire, rubber insulated wire, nitrile polyvinyl chloride mixture insulated wire, agricultural underground direct-buried aluminum core plastic insulated wire, cotton yarn textile soft insulated wire, nylon sheathed polyvinyl chloride insulated wire, flexible polyvinyl chloride insulated wires for power and lighting, and more.
03. In what scenarios are cable trays suitable?
Answer: Cable trays are ideal for overhead installations of power and control cables indoors and outdoors in general industrial and mining enterprises. They can also be used indoors and outdoors in telecommunications, radio, and television departments.
04. What are cable accessories?
Answer: Common electrical accessories include cable terminal junction boxes, cable intermediate junction boxes, connecting pipes and terminals, steel plate wiring troughs, cable trays, etc.
05. What is a cable joint?
Answer: A device that connects the conductors, insulating shielding, and protective layers of cables to connect cable lines is called a cable joint.
35 issues that must be known about wires and cables during the construction of Yatel weak current projects:
06. What is the main electrical wiring?
Answer: The main electrical wiring refers to the connection method of the main electrical equipment and busbars in power plants and substations, including the connection method of the main busbar and the factory power system according to certain functional requirements.
07. What regulations should be followed when selecting the cross-section of a power cable?
Answer: When selecting power cables, the following principles should be followed: 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 wire core must meet the stability requirements when the power supply system is short-circuited; 4) Check whether the voltage drop meets the requirements based on the cable length; 5) The smallest short-circuit current at the end of the line should enable the protection device to operate reliably.
08. What are the advantages of cross-linked polyethylene cables compared to oil-paper cables?
Answer: 1) Easy to install due to smaller bending radius and lighter weight; 2) Not affected by line drop; 3) Excellent thermal performance, allowing for high operating temperatures and larger transmission capacities; 4) Simple cable accessories, all of which are dry structures; 5) Easy operation and maintenance, no oil leakage issues; 6) Lower cost; 7) Higher reliability and lower failure rates; 8) Fewer manufacturing processes, simpler procedures, and significant economic benefits.
09. What are the requirements for fixing AC single-core cable clamps? Why?
Answer: The clamp should not contain any ferrous parts to form a closed magnetic circuit. This is because when the cable core passes through current, a magnetic field is generated around it, and the strength of the magnetic field is proportional to the magnitude of the current passing through the wire core. If ferromagnetic materials like iron parts are used, eddy currents will be generated in the iron parts according to electromagnetic induction, heating up the cable and potentially damaging it. Therefore, iron parts cannot be used as fixing clamps for single-core AC cables.
10. What are the main features and advantages of heat-shrink cable head accessories?
Answer: The biggest feature of heat-shrink accessories is the use of stress tubes instead of traditional stress cones. This not only simplifies the construction process but also reduces the size of the terminal of the joint, making it easier to install, saving time and labor, providing superior performance, and conserving metal. Heat-shrink cable accessories combine the advantages of the filling type and the dry-pack type.
35 issues that must be known about wires and cables during the construction of Yatel weak current projects:
11. What inspections should be carried out before cable laying?
Answer: 1) The brackets should be complete and painted intact; 2) The cable model, voltage, and specifications should comply with the design; 3) The cable should be well-insulated, and if there is doubt about the sealing of oil-paper cables, moisture should be checked; direct-buried cables and small-bottom cables should pass the DC voltage resistance 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 less than 1.47MPa.
12. When you have doubts about the seals of oil-paper insulated power cables, how can you use a simpler method to check if the cable insulation paper is damp?
Answer: Light the cable insulation paper or place it in cable oil at around 150°C for inspection. If there is no "hissing" sound or white foam appears, it indicates that it is not damp.
13. What should be indicated on cable signs? What are the requirements for writing?
Answer: The cable line design number, cable model, specification, and starting point should be indicated on the signboard, and cables used in parallel should have sequence numbers. It is required to have clear handwriting and not easily fall off.
14. Where should the orientation signs of direct-buried cables be set?
Answer: At both ends of the cable, at the cable joints within 50-100 meters in the straight-line section of the cable, and at the corners where the cable changes direction.
15. How to remove moisture before construction for yellow wax tapes, black glass paint tapes, alkali-free glass tapes, etc.?
Answer: 1) Constant temperature drying method: Roll the insulating tape into a small roll of 25-30mm in diameter, put it in a constant temperature drying box of 110-120°C for 4-5 hours, cool it and take it out, and put it into a dry sealed cylinder. 2) Oil immersion moisture removal method: Place the small roll of the insulating tape into cable oil with a constant temperature of 120-130°C, keeping a distance of 30mm from the bottom of the pot. After a certain period of time, when the oil surface no longer produces foam, remove it and place it into a barrel with cable oil. The oil level should exceed all loaded objects and seal it.
16. What is the function of the cable outer sheath?
Answer: To protect the inner protective layer from mechanical damage and chemical corrosion, and to enhance mechanical strength.
17. What requirements should outdoor cable trenches meet?
Answer: The top of the cable trench should be slightly higher than the ground. Concrete cover plates should be used. The cable should be placed flat on the brackets and there should be good drainage pipes.
18. What is the function of the inner protective layer of the cable?
Answer: To prevent the insulation layer from coming into contact with water, air, or other objects, to prevent the insulation from getting damp and the insulation layer from being mechanically damaged.
19. What should you pay attention to when using wire cutters?
Answer: Before use, make sure to check if the insulation of the insulating handle is intact. When using, do not cut metal wires that exceed the allowable specifications. It is prohibited to use wire cutters as hammers to avoid damage.
20. What is insulation strength?
Answer: Insulating substances in an electric field will break down when the electric field strength reaches a certain limit. The electric field strength that causes insulation breakdown is called insulation strength.
21. What are the advantages of crosslinked heat-shrink cable accessories?
Answer: This is a new type of material. Compared with other types of accessories, it has the advantages of superior electrical performance, small size, light weight, simple installation, and material matching. In addition, it also has the ability to resist climate, anti-fouling, flame retardant, and self-extinguishing.
22. What are the requirements for the mechanical strength of the cable conductor connection points?
Answer: The mechanical strength of the connection point is generally lower than the tensile strength of the cable conductor itself. For fixedly laid power cables, the tensile strength of the connection point is not less than 60% of the tensile strength of the conductor itself.
23. What are the main properties of the insulation layer material of the power cable?
Answer: It should have the following main properties: 1) high breakdown strength; 2) low dielectric loss; 3) quite high insulation resistance; 4) excellent discharge resistance; 5) certain softness and mechanical strength; 6) long-term stability of insulation performance.
24. What are the regulations on traction strength when laying cables mechanically?
Answer: For copper-core cables, the allowable traction strength is 70N/cm when pulling the head; for aluminum-core cables, the allowable traction strength is 40N/cm when pulling the head; if traction is made with a wire mesh sleeve, the allowable strength is 10N/cm when pulling; and for lead-sheathed cables, it is 40N/cm.
25. What are the regulations on cable protection pipes?
Answer: 1) When a cable needs to be laid through a protective pipe, the inner diameter of the pipe should not be less than 1.5 times the outer diameter of the cable, and the inner diameter of concrete pipes, clay pipes, asbestos, and cement pipes should not be less than 100mm; 2) The bending radius of the cable pipe should comply with the bending radius of the penetrated cables; 3) Each pipe should not exceed three elbows, and there should not be more than 2 right-angle bends.
26. How to measure the outer diameter of the cable sheath?
Answer: Measure the outer diameter of the sheath at five evenly distributed points on the circumference and calculate the average value, which is the outer diameter of the sheath.
27. How to connect copper core cables with different cross-sections?
Answer: When connecting copper core cables with different cross-sections, open-type copper connectors can be used, soldered, or pure copper rods can be connected to copper connectors according to different cross-section requirements, and connected by crimping method.
28. Briefly describe the process of heat-shrinking production of indoor terminal heads in 10KV crosslinked cables?
Answer: 1) Preparation stage: Check whether the heat-shrinkable cable accessories are complete and whether the models are matched. After checking and confirming whether the cable is damp, check the cable; 2) Cut off the excess cable and decide the cable length according to the on-site situation; 3) Peel the protective layer; 4) Weld the grounding wire and weld the grounding wire on the steel strip; 5) Fill the three-fork and wrap sealant; 6) Install the three-core branch sheath, put the sheath into the root, start to shrink from the middle, first to the root, and then to the finger; 7) Peel the copper belt and the outer semiconductor layer, peel and cut the copper belt with a mouth of more than 20mm of the three-core branch sleeve. It is strictly forbidden to damage the main insulation and remove the semiconductor layer; 8) Install the stress tube, and the support sleeve at the end of the pipe is docked and heat shrink; 9) Install the wiring terminals; 10) Install the insulating tube; 11) Install the sealing tube; 12) Install the phase color tube after the core phase.
29. What are the steps to install prefabricated terminals in indoor and outdoor environments?
Answer: 1) When a cable needs to be laid through a protective pipe, the inner diameter of the pipe should not be less than 1.5 times the outer diameter of the cable, and the inner diameter of concrete pipes, clay pipes, asbestos, and cement pipes should not be less than 100mm; 2) The bending radius of the cable pipe should comply with the bending radius of the penetrated cables; 3) Each pipe should not exceed three elbows, and there should not be more than 2 right-angle bends.
30. What are the regulations on cable protection pipes?
Answer: 1) For the power system: The wire and cable products used in the power system mainly include overhead bare wires, busbars (busbars), power cables (plastic cables, oil-paper cables (basically replaced by plastic power cables), rubber-covered cables, overhead insulated cables), branch cables (replaced with some busbars), electromagnetic wires, and electrical equipment wires and cables for power equipment.
Answer continued: 2) For the information transmission system: The wires and cables used in the information transmission system mainly include local telephone cables, TV cables, electronic cables, radio frequency cables, fiber optic cables, data cables, electromagnetic wires, power communications or other composite cables, etc.
31. Five categories of wire and cable products:
(1) Bare wires and bare conductor products: The main features of this type of product are: pure conductor metal, without insulation and sheathing layer, such as steel core aluminum stranded wire, copper-aluminum busbar, electric locomotive wire, etc.; the processing technology is mainly pressure processing, such as smelting, calendering, drawing, twisting/pressure twisting, etc.; the products are mainly used in suburban areas, rural areas, user main lines, switch cabinets, etc.
(2) Power cable: The main features of this type of product are: extruding (wrapping) the insulating layer outside the conductor, such as overhead insulated cable, or twisting several cores (corresponding to the phase, neutral and ground wires of the power system), such as overhead insulated cables above two cores, or adding a sheath layer, such as plastic/rubber-sleeved wire and cables. The main process technologies include drawing, twisting, insulating extrusion (wrapping), cable formation, armor, protective layer extrusion, etc. The different process combinations of various products are different. The products are mainly used for the transmission of strong electric power in the transmission, distribution, transmission, conversion and power supply lines. The current through the flow is large (ten to thousands of amperes) and the voltage is high (220V to 500kV and above).
(3) Electrical equipment wires and cables: The main characteristics of this type of product include a wide variety of specifications, a wide range of applications, and a large number of voltages of 1kV or below. New products are constantly derived in special occasions, such as fire-resistant cables, flame-retardant cables, low-smoke, halogen-free/low smoke and low-halogen-low-halogen-low-termite-proof cables, mouse-resistant cables, oil-resistant/cold-resistant/temperature-resistant/wear-resistant cables, medical/agricultural/mining cables, thin-walled wires, etc.
(4) Communication cables and fiber optics: With the rapid development of the communications industry in the past twenty years, products have also developed at an astonishing speed. From the simple telephone and telegram cables of the past to thousands of pairs of speech cables, coaxial cables, optical cables, data cables, and even combined communication cables. This type of product is usually small and uniform in structural dimensions, and has high manufacturing accuracy requirements.
(5) Electromagnetic wire (winding wire): mainly used in various motors, instruments, etc. The derivatives/new products of wires and cables are mainly generated due to the requirements of different application occasions, different application requirements, convenience of equipment and reduced equipment costs, etc., and the use of new materials, special materials, or changing the product structure, or improving process requirements, or combining different varieties of products; different materials such as flame retardant cables, low-smoke, halogen-free/low-smoke, low-halogen-low-halogen-low-halogen-low-termite-proof cables, mouse-proof cables, oil-resistant/cold-resistant/temperature-resistant cables, etc.; changing the product structure such as fire-resistant cables, etc.; improving process requirements such as medical cables, etc.; combining products such as OPGW; facilitating installation and reducing equipment costs such as prefabricated branch cables, etc.
32. What inspections should be carried out after the busbar device is completed?
Answer: The following inspections should be carried out: 1) The processing, preparation, and welding screw connections of metal components should comply with the regulations; 2) The bolts, washers, opening pins, and other parts should be complete and reliable; 3) The busbar preparation and mounting frame should comply with the regulations, and the electrical distance between phases and ground meets the requirements; 4) The porcelain parts, iron parts, and glued parts should be complete, the oil filling sleeve should be free of oil leakage, and the oil level should be normal; 5) The paint is complete, the color is correct, and the grounding is good.
33. Among the power cable connectors below 35kv and below, there are several methods to improve the electric field distribution at the sheath disconnection (please list five), and briefly describe their methods.
Answer: 1) Flared horn: Pry the edge of the lead bag at the cutting point of the lead bag, and it becomes a horn-shaped edge, and its edge should be smooth, round, and symmetrical; 2) Reserve the whole package insulation: Leave a piece of round-pack insulating paper between the lead bag cut and the separation point of the cable core wire; 3) Cut off the semiconducting paper: Cut the semiconducting paper below the horn-shaped mouth; 4) Wrap the stress cone: Wrap it into a cone shape with an insulating tape and conductive metal material, artificially expand the shielding layer to improve the electric field distribution; 5) Equipotential method: For dry-pack or crosslinked polyethylene cable heads, a metal strip is wrapped on the insulating surface of each wire core profile and connected them together; 6) Install stress control tubes: For 35kv and lower heat shrink tube cable heads, first wrap the 2-layer semiconductor strip from the end direction of the copper shield layer of the wire core through the semiconductor tape to the insulating surface of the wire core, and then fold the stress tubes of the corresponding specifications at the end of the copper shield and heat shrink forming.
34. What requirements should the processing of cable brackets meet?
Answer: 1) The steel should be straight without obvious distortion, the cutting error should be within 5mm, the cut should be without curled edges and thorns; 2) The bracket should be firmly welded without deformation, and the vertical clear distance between the horizontal braces and the design deviation should not be greater than 5mm; 3) The metal bracket must be subject to anti-corrosion treatment. When located in damp heat, salt, fog, and chemically corrosive areas, special anti-corrosion treatment should be carried out according to the design.
35. What requirements should be met when laying cables?
Answer: The following requirements should be met: 1) In terms of safe operation, avoid various external damages as much as possible, and improve the power supply reliability of cable lines; 2) In terms of economics, consider from the perspective of investment savings; 3) In terms of construction, the path of cable lines must be convenient for rotary work and maintenance after operation.
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