What should we pay attention to when installing cables?

Matters needing attention in Electrical cable installation:

1. Keep a distance of 2m when the mine cable is installed in parallel with the heating pipeline, and keep 0.5m when crossing.
2. When the cable is installed in parallel or across other pipes, a distance of 0.5m must be maintained.
3. When the cable is directly buried, the depth of the 1-35kV cable should not be less than 0.7m.
4. When the cables of 10kV and below are installed in parallel, the mutual clear distance is not less than 0.1m, the 10-35kV is not less than 0.25m, and the distance when crossing is not less than 0.5m.
5. The minimum bending radius of the cable must not be less than 15D for multi-core cables and 20D for single-core cables (D is the outer diameter of the cable).

6. Cable joints of 6kv and above.
A. When installing the cable terminal head, the semi-conductive shielding layer must be stripped off, and the insulation must not be damaged during operation. Knife marks and unevenness should be avoided, and sandpaper should be used to smooth it if necessary; the shielding end should be flat and graphite The layer (carbon particles) is removed.
B. The copper shield and steel armor of the plastic insulated cable end must be well grounded. This principle should also be followed for short circuits to avoid induced electromotive force at the end of the steel armor during unbalanced operation of three-phase, or even “fire” and burn the sheath Wait for the accident. The grounding lead wire should be tinned braided copper wire, and soldering iron should be used when connecting with the copper tape of the cable. It is not suitable to use a blowtorch to seal and solder, so as to avoid burning insulation.
C. The three-phase copper shield should be connected to the ground wire separately. Note that the shield ground wire and the steel armor ground wire should be led out separately and insulated from each other. The position of the welding ground wire should be as low as possible.
7. The basic requirements for cable ends and intermediate joints: a. Good conductor connection; b. Reliable insulation, it is recommended to use radiation cross-linked heat-shrinkable silicone rubber insulating materials; c. Good sealing; d. Sufficient mechanical strength, Can adapt to various operating conditions.

8. Electrical Power Cable end must be waterproof and corroded by other corrosive materials to prevent breakdown due to aging of the insulation layer caused by water trees.
9. Cable loading and unloading must use cranes or forklifts. Horizontal transportation or laying flat is prohibited. When installing large cables, cable cars must be used to prevent cables from being damaged by external forces or scratching the insulation layer due to manual dragging.
10. If the cable cannot be laid in time for some reason, it should be stored in a dry place to prevent sun exposure and water ingress into the cable end.

Precautions for testing cross-linked cables

In recent years, silane cross-linked polyethylene cable material (hereinafter referred to as XLPE) has become the leading material for low-voltage cross-linked cable insulation because of its simple manufacturing equipment, mature technology, convenient operation, and low overall cost.

At present, the commonly used XLPE is the two-step XLPE. When the cable factory produces the insulated core, the polyethylene (PE) grafted with silane and the catalyst masterbatch are mixed in a certain proportion and extruded in a common extruder. Then complete the cross-linking in hot water or steam; the other one-step method XLPE is made by the cable material manufacturer, which mixes all the raw materials together by a special method according to the ratio, and the cable factory directly completes the grafting and grafting in one step in the extruder. Extrude the insulated core, and then complete the cross-linking under natural conditions. The common point of these two types of XLPE is that no special extrusion equipment is needed and the cross-linking process is relatively simple. As long as the raw materials and process conditions meet the requirements, it can be made into an insoluble and infusible thermosetting plastic. Compared with thermoplastic PE, its heat-resistant deformation and mechanical properties at high temperature, environmental stress cracking, aging resistance, chemical resistance, etc. have been improved or improved, while the electrical properties remain basically unchanged, and the long-term work of the cable The temperature is increased from the original 70°C to 90°C, thereby improving the short-term current withstand capability of the cable. In summary, XLPE low-voltage cables have become the main products of cable manufacturers in recent years.

As a third-party inspection agency, this type of cable is also increasing year by year. How to accurately provide the test results of the thermal extension and aging performance of this type of product? Inspectors are faced with some special circumstances. The following is an analysis:

First, the problem of abnormal thermal extension of XLPE insulation. When testing, the author often finds that the elongation rate of XLPE cable insulation under load in the 200℃ thermal extension test greatly exceeds the requirements specified in the standard, or the sample is put into the oven and melted in a short time. If the test is repeated immediately with the original sample, The reproducibility of the results is very good. According to the routine, as long as the test method is correct and the sampling is correct, a conclusion can be drawn based on the test results. However, for XLPE, this may be a great risk. Because the cross-linking process of ACWU90 AC90 Cable is a slow chemical change process related to temperature, humidity, time, insulation thickness and other factors, especially the naturally cross-linked XLPE insulation material is affected by the above factors to complete the cross-linking. There will be a big difference in time, and it is entirely possible that the natural cross-linking has not been completed within the prescribed test period. Once the natural cross-linking is completed over time, its performance may meet the requirements of national standards. For such situations, the author believes that under the premise of reflecting the current situation of the sample, we should not rush to determine, but should provide the sample with a condition to promote crosslinking-soaking in hot water at 90°C±2°C Do the hot extension test after 4 to 5 hours. Practice has proved that the test results at this time can be used as a basis for judgment. It is worth mentioning that individual manufacturers are pursuing commercial profits one-sidedly, using the similar characteristics of PE and XLPE to pretend to be XLPE, and PE will not produce cross-linking changes no matter what conditions are provided to promote cross-linking. In terms of performance, it does not meet the requirements of XLPE at all, which is the same as the fact that stones cannot hatch chicks. This requires inspectors to have the ability to identify true and false, good and bad XLPE. In fact, through observation and work accumulation, we can distinguish whether the tested sample is under-crosslinked, inferior XLPE, or PE is used according to the fusing time and fusing point after the sample is placed in the oven. However, as a third-party inspector, you cannot draw conclusions based on experience alone, and must make judgments based on real data.

Second, the problem of the change rate of XLPE heat aging test exceeding the standard. When testing, if you get the sample, prepare it immediately, and put it in the oven for aging as usual, the tensile strength and elongation at break will often exceed the standard after aging, and you must be cautious in judging this result. This phenomenon is not entirely caused by poor aging performance, it may be because XLPE has not been completely cross-linked (from the time curve of XLPE cable material thermal extension with warm water placement, it can be seen that when the thermal extension is qualified, it does not represent the sample Completely cross-linked), and after being placed in the aging box, XLPE is still completing its cross-linking process, which leads to an increase in tensile strength, a decrease in elongation at break, and the final rate of change exceeds the standard. Due to the long time to complete the aging, it will be troublesome to discover the problem once the test is over. Therefore, it is necessary to thoroughly crosslink the sample before performing the aging test.

In summary, it can be seen that special factors should be considered to determine the thermal elongation and thermal aging performance of XLPE. Personnel engaged in third-party inspections can neither make a hasty conclusion on the results of the test, because doing so involves the risk of misjudging qualified products as unqualified; nor can they avoid these two tests because it is difficult to draw conclusions. This may cause substandard products or counterfeit products to be missed. Therefore, it is necessary to exclude the possibility that the sample has not been cross-linked or completely cross-linked before performing the above two tests. We advocate the use of scientific and reasonable test methods to provide fair and reliable test results.

The structure and specification of YJV cable

Let me introduce to you what YJV means, yj means cross-linked polyethylene, v means polyvinyl chloride, then YJV is cross-linked polyethylene insulated PVC sheathed cable, and the range of use is for the rated voltage (U0/U) 0.6/1—26/35kv power line transmission and distribution, the rated temperature of the cable conductor is 90 degrees when in use, and the temperature of the cable conductor does not exceed 250 degrees when short-circuited (the duration does not exceed 5S). It has the advantages of light weight and simple structure, so it is widely used in urban power grids.
YJV cable model specification

The cores of YJV cables are single core, 2 cores, 3 cores, 4 cores, 5 cores, 3+1, 3+2, 4+1. 3+1 represents 3 phase wires and 1 ground wire, 3+ 2 represents 3 phase wires and 2 ground wires, 4+1 represents 4 phase wires and 1 ground wire. According to the standard model, the specific size specifications include: 1 square, 1.5 square, 2.5 square, 4 square, 6 square, 10 square, 16 square, 25 square, 35 square, 50 square, 70 square, 95 square, 120 square, 150 Square, 185 square, 240 square, 300 square. For example, the YJV 3*120+2*70 cable is a cable composed of three 120 square phase wires and two 70 ground wires.

The combination between the ground wires is regulated by the standard, so the 70 square behind the YJV 3*120+2*70 cable can be omitted. The main specifications of the YJV cable range from 1 square to 240 square meters (also can be customized separately). It is a cable used for transmission and distribution of electric energy. It is often used in urban underground power grids, lead-out lines of power stations, internal power supply of industrial and mining enterprises, and underwater transmission lines that cross rivers and seas. In power lines, the proportion of cables is gradually increasing. Power cable is a cable product used to transmit and distribute high-power electrical energy in the main line of the power system, including 1-500KV and above various voltage levels, various insulated power cables.

How to prevent the electric power cable fire

The selection of XLPE insulated power cables should follow the following principles: the rated voltage should be greater than or equal to the voltage at the installation point.          

1. Short-circuit fault caused by insulation damage

The protective layer of the cable will be damaged during the laying process, or the insulation layer of the cable will be damaged by mechanical damage during the operation, resulting in interphase or damage to the protective layer of the cable, and the arc will cause the protection of the insulating material and the outer layer of the cable. The layer material burns and catches fire.

2. Long-term overload operation of the cable

Long-term overload operation, the working temperature of the cable insulation material exceeds the higher allowable temperature of normal heating, thereby accelerating the insulation aging of the cable. This insulation aging phenomenon usually occurs in the entire cable line. Due to the aging of the cable insulation layer, the insulation material will lose or reduce the insulation layer and mechanical properties, so it is easy to break and catch fire, and even burn in many places along the entire length of the cable.

3. Insulation breakdown of the intermediate junction box

The intermediate joint of cable joint box is oxidized, heated and gummed during operation due to loose crimping, weak welding or improper joint material selection; When making the cable intermediate joint, the quality of insulating agent poured into the intermediate joint box does not meet the requirements. When pouring the insulating agent, there are air holes in the box and the cable box is poorly sealed and damaged, which causes moisture leakage. The above factors can cause insulation breakdown, form short circuit, and cause cable explosion and fire.

4.Cable head burning

Because the surface of the cable head is contaminated by moisture, the porcelain sleeve of the power cable head will break, and the distance between the wires will be too small, which will cause arcing and fire, which will cause the cable head and the surface of the cable to be insulated. The insulation of the outlet is burning.

5. Cable fire caused by external fire and heat source

For example, the spread of fire in the fuel system, the explosion of the fuel circuit breaker, the spontaneous combustion of pulverized coal in the boiler crushing system or coal conveying system, the baking of high-temperature steam pipes, the chemical corrosion of acid and alkali, welding sparks, etc. may cause the cable to catch fire.

How to distinguish the quality of aluminum alloy cables

Conductor, insulation and armored sheath are necessary for the composition of aluminum alloy cables. The quality of aluminum alloy cables mainly depends on the aluminum alloy conductor rods and cable insulation. Aluminum alloy cables have very good performance, corrosion resistance, and mechanical Performance, bending performance, flexibility, etc.
1. Aluminum alloy conductor rod
See if we can independently produce high-quality aluminum alloy conductor rods:
1. At present, there are not many manufacturers with independent aluminum alloy conductor production technology. They have aluminum alloy conductor rod production lines that can be continuously smelted, continuous casting, continuous casting and rolling. If they do not have independent aluminum alloy conductor rod production capacity, rely on Consignment processing, so-called secret smelting, or other aluminum alloy conductor rods purchased without a formal source not only cannot ensure the basic quality of aluminum alloy cables, but also cannot control the quality of the cables from the source.
2. In addition to the aluminum alloy conductor rod production line with smelting, continuous casting, continuous casting and rolling, it also depends on the size of the continuous casting billet section of its production line. The larger the section, the better the quality of the rolled aluminum alloy rod. Excellent, “good steel is made by hard work.” Excellent aluminum alloy conductor rods are the decisive factor for the electrical and mechanical properties of aluminum alloy cables. If you do not have high-quality aluminum alloy rods, no matter how drawing, stranding, cabling, armoring, etc., the subsequent processes cannot be changed The basic quality of its conductor.

2. Cable insulation
There are three things to look at with regard to insulation; cross-linking degree, stranded conductors, and conductor cable annealing:
1. Cross-linking degree: One of the advantages of aluminum alloy cables over copper cables is that all aluminum alloy cables are insulated with cross-linked polyethylene, and the operating temperature of the cable is 90 degrees. It is precisely because of the use of cross-linked polyethylene insulation that there is a problem of cross-linking degree. Regular professional aluminum alloy cable manufacturers should have a special cross-linking room.
2. Stranded conductor: Look at the conductor stranding technology and conductor stranding production line. At present, the stranded conductor equipment in the domestic cable industry is basically the same. The stranded conductor produced usually produces aluminum chips and burrs, which damage the insulation and affect the insulation. Effect, cause safety hazards and shorten insulation life. The advanced stranded conductor equipment is a sub-motor type, PLC program-controlled nano-technology conductor stranding equipment. Using this advanced process equipment, computer-controlled production programming, and innovative top-level nano-technology, the aluminum alloy conductors produced have no aluminum on the surface Chips, no burrs, no oil, no bumps, no scratches, no scratches, can effectively ensure that the cable insulation is free from any damage and destruction, and the service life of the product is much higher than that of similar products.
Third, the performance of aluminum alloy cables
1. Corrosion resistance: The corrosion resistance of pure aluminum is better than that of copper, but the corrosion resistance of aluminum alloy is better than that of pure aluminum, because the chemical elements such as rare earth added to aluminum alloy can increase the corrosion resistance of aluminum alloy, especially The performance of electrochemical corrosion resistance solves the long-term electrochemical corrosion problem of pure aluminum at the joint.
2. Mechanical properties: tensile strength and elongation. Compared with pure aluminum conductors, aluminum alloy conductors have added special ingredients and adopted special processing techniques to greatly improve the tensile strength, and the elongation rate is increased to 30%, making it safer and more reliable to use.
3. Bending performance: The bending performance of the aluminum core cable is very poor, and the bending is easy to break. The bending radius of the aluminum alloy power cable is 7 times the outer diameter of the cable, which is far better than the GB/T12706 “small bending when the cable is installed. 10 to 20 times the outer diameter of the cable specified in “Radius”.

4. Flexibility: As long as the pure aluminum cable is twisted at a certain angle for a few times, the conductor will crack or break, which is easy to cause accidents. The aluminum alloy power cable can withstand dozens of bends, eliminating the installation and use of pure aluminum cables in the past. The hidden dangers of accidents occurred during the process, which greatly improved the safety and reliability.
5. Aluminum alloy conductor is an emerging conductor material formed by adding rare earth, magnesium, copper, iron and other elements to pure aluminum through alloy technology. As we all know, after adding other alloying elements to aluminum, the electrical conductivity will decrease. However, through process control, the electrical conductivity can be restored to a level close to that of pure aluminum, making it have a current carrying capacity similar to that of pure aluminum.
6. Pure aluminum has poor creep resistance. The thermal expansion and contraction caused by power-on and power-off will cause a large amount of creep at the connection. After a long time, it will relax, and the contact resistance will increase and cause overheating, which is easy to cause accidents. The creep resistance of AA8000 series aluminum alloy is 300 of that of pure aluminum conductor, which greatly reduces the possibility of cable joint slack and improves the connection of conductors.

Is it better to use ordinary wires for household decoration or flame retardant wires?

Regarding this problem, it has always been a problem that owners have struggled with during decoration. Although each has its own advantages, it is recommended to use flame-retardant wires and higher safety performance when conditions permit.

The advantages of flame-retardant wires: in the event of a fire, the flame spread speed can be controlled within a certain range to avoid major disasters caused by the prolonged combustion of the wires, fight for rescue time, keep various equipment, and avoid greater losses.
Difference from ordinary wires: most ordinary insulated wires and flame-retardant wires have no difference in appearance, but flame-retardant wires contain flame-retardant components in the outer plastic insulation layer, while ordinary wires do not; flame-retardant wires are also classified as ZA ZA, ZB and ZC have three levels of flame retardant effects. ZA has a higher and better flame retardant rating. It is generally used in military, aviation and municipal engineering. The flame retardant effects of ZB and ZC can be used for ordinary household decoration.

Do I need to use flame-retardant wires for home decoration?
Homes have strict acceptance standards for engineering constructions, requiring that such places must use flame-retardant wires; at the same time, the fire department and engineering supervisors conduct spot checks on the construction wires, and the wires can only be constructed after they have passed the flame retardant performance. Therefore, in terms of home furnishings, flame-retardant wires can meet household electricity needs.

In the home decoration, the wires are concealed projects. Once damaged, it will be more troublesome to repair. Therefore, try to use wire and cable products with higher safety performance, and use it more safely.


The difference between fire-resistant cable and flame-retardant cable

Flame retardant wire and cable, its flame retardant means that when a wire and cable fire accident occurs, it can block and delay the spread and extension of the flame along the wire and cable, and minimize the expansion of the wire and cable fire range. This type of cable has a self-defense after fire. The characteristics of extinguishing. Generally, it can be understood that when the wire and cable product catches fire by itself or by an external heat source, after the fire source subsides, the wire and cable product no longer burns, or the burning time is very short.

Fire-resistant wire and cable means that in a wire and cable fire accident, the wire and cable product can maintain normal operation for a certain period of time while the external flame is still burning, maintain the integrity of the wire and cable circuit and maintain the normal operation of the line equipment.

Both fire-resistant cables and flame-retardant cables are suitable for wiring of control, signal, protection and measurement systems with a rated voltage of 750V and below.
The structure and materials of fire-resistant cables are different from those of flame-retardant cables. The basic structure of flame-retardant cables is:
(1) The insulating layer is made of flame-retardant materials.
(2) The sheath and outer sheath are made of flame-retardant materials.
(3) The wrapping tape and filling are made of flame-retardant materials.

Fire-resistant cables usually add a fire-resistant layer between the conductor and the insulating layer, so theoretically, a fire-resistant layer can be added to the structure of the flame-retardant cable to form a flame-retardant and fire-resistant cable. Because of the fire-resistant layer of fire-resistant cables, multi-layer mica tapes are usually used to wrap the wires directly. It can withstand long-term burning, even if the polymer at the place where the flame is applied is burned, it can ensure the normal operation of the line.

Commonly used aluminum alloy wire varieties and product advantages

The commonly used aluminum alloy wire varieties are as follows:
1. High-strength aluminum alloy wire
High-strength aluminum alloy wire is an aluminum alloy product with magnesium and silicon added to aluminum and processed to obtain sufficient strength, plasticity and electrical properties, deformation and heat treatment. It is the largest and most widely used aluminum alloy variety of aluminum alloy transmission lines. The electrical conductivity of high-strength aluminum alloy wire is 53% IACS, which is almost twice that of ordinary aluminum wire, and the single-wire strength of aluminum alloy is greater than 300Mpa. The strength of ordinary aluminum single wire is 150~170Mpa, and aluminum alloy wire has a greater advantage in strength.



2. Heat-resistant aluminum alloy wire
Heat-resistant aluminum alloys are classified into heat-resistant aluminum alloys with an electrical conductivity of 58% IACS and high-conductivity heat-resistant aluminum alloys in which yttrium is added to aluminum. Since the current carrying capacity of the wire used at 150°C can be increased by 61-69% than that of the wire used at 90°C, the heat-resistant aluminum alloy can be used as a compatible wire. The high-strength performance of high-strength heat-resistant aluminum alloy wire can improve its dynamic stability under short-circuit or overload conditions; its heat resistance can improve thermal stability. The super heat-resistant aluminum alloy and ultra-high heat-resistant aluminum alloy to be developed can further improve the current-carrying capacity and heat resistance of the wire, and further increase the long-term use temperature to 180°C, 210°C and 230°C.
Compared with traditional ACSR, high-strength aluminum alloy wire and heat-resistant low-resistance aluminum alloy wire have the following advantages:
(1) Under the same unit weight, the DC resistance of the aluminum alloy conductor is low. , The current capacity is large, the pulling force is large, the unit weight is larger than the pulling force;
(2) Compared with the condition of the same current-carrying capacity, aluminum alloy wire has the advantages of lighter weight, greater tensile force, and greater tensile force per weight. Aluminum alloy wire is a single material wire, easy to install and construct.
(3) The carrying hazard level of aluminum alloy conductors is low;
(4) The service life of ordinary steel core aluminum stranded wire is about 50 years, and the service life of aluminum alloy wire is more than 100 to 120 years.

The main functions and advantages of ACSR

在先进科学技术的现代时代,许多现代工业设施已经出现在我们的世界中并存在于我们的生活中。钢芯铝绞线也是在电力中起重要作用的主要力量。ACSR是由单层或多层铝绞线在镀锌钢芯外部绞合而成的增强钢丝。内部是钢“芯”,外部通过绞合用铝线包裹在钢芯上。; 钢芯主要用于增加强度,铝绞线主要用于传输电能。它在电力和输电线路行业中占有重要地位。对于高压传输线,由于线路的路径有限,因此无法将其安装在一条路径上。对于多行,人们想出了一种使用一条路径,一组铁塔和多根电线的方法,即一条线相当于多条线。对于500KV输电线路,我国大部分地区采用悬挂四根电线的方法。这种接线方法称为同塔并联。这就是为什么某些杆用于“ L J”和“ LGJ”的主要原因。


钢芯铝绞线的缩写:“ LGJ”是绞合的铝线和钢丝,普通铝绞线“ L J”主要用于架空输电线路。ACSR的内部为钢“芯”,外部通过绞合用铝线包裹在钢芯上。钢芯主要增加强度,而铝绞线主要传输电能。它们都是裸线,用途基本相同,型号规格不同。
普通铝绞线:型号以“ L J”表示,为裸线。目前,中国一般使用铝包钢绞线(LGJ)作为导体。钢芯主要用于增加强度,铝绞线主要用于传输电能。根据电压的不同,导线的截面积也不同。例如,500 kV传输线的电流导体通常使用LGJ-400 / 35导体。其中,L是铝线的缩写,G是钢芯的缩写,J是绞线的缩写,400是铝的400平方毫米,而35是钢的35平方毫米。

How to distinguish between national standard wires and inferior non-standard wires

Before moving into a new house, everyone will check the house first, but most citizens will focus on the structure of the house, and they rarely care about the wires inside the walls. If the house is compared to a person, then the wires hidden in the walls are the vital “arteries”. The wires for home improvement not only concern the normal daily life of the family, but also the safety of the family’s relatives. Inferior wires may cause short circuits, Electric shock, damage to electrical equipment, and even fire, causing casualties. Nowadays, a large number of non-standard wires and low-quality counterfeit wires are flooding the building materials market. Some low-quality wires are broken as soon as they are twisted, making it easier to distinguish. But some low-quality wires are exquisite in workmanship, and at first glance they seem to be even better than the national standard! How to distinguish between national standard wires and inferior non-standard wires? Huaxing Cable‘s professional electrician technicians suggest that you should never think about saving money when buying home improvement wires. The quality of the wires not only affects the service life and safety of household appliances associated with them, but also affects the life safety of our family members. Now let the professional electrician technician of the cable explain to you how to distinguish between the national standard wire and the inferior non-standard wire!

The first step in identifying wires: look at the wire signsThe national standard wire label is the product qualification certificate. Take the wire qualification certificate as an example, it is printed with: wire product trademark, wire product name, wire manufacturer name, wire production site, cable manufacturer contact number, CCC certification and aerial bundled cable b230 factory number, wire model specification , National standard, rated voltage, length of wire, cross-sectional area of ​​wire conductor, production date, inspector’s seal. At the same time, well-known brand wire manufacturers generally have anti-counterfeiting labels that cannot be imitated! Each coil of the aerial bundled cable(abc) b231  has an anti-counterfeit QR code and a barcode, double anti-counterfeiting, just like our ID number

Inferior non-marking signs do not have the above content or are incomplete, and even if they have, they cannot be investigated. The following low-quality line signs are taken as an example; the trademark and company name are all virtual, although the factory address is available, but not specific, there is no way to find the phone number, the model column is blank, and the specification column is only marked 2.52. The formal marking should It is the number of conductor cores × conductor diameter, that is, 1×1.78 mm. The inspector’s seal is printed together with the other contents of the sign, which means that there is no need for inspection at all, and there is no anti-counterfeiting label.

The second step is to look at the copper wire conductor

Qualified copper core wires should be oxygen-free copper, purple-red, shiny, and soft to the touch.

The fake and inferior copper core wire is purple-black, yellowish or white, with many impurities, poor mechanical strength, poor toughness, and it will break with a little force, and there are often disconnections in the wire. The picture below is a low-quality copper-clad copper wire.

The third step is to look at the insulation material

The insulating layer of the national standard wire is made of high-quality insulating plastic, which has a certain degree of mechanical strength and flexibility, and cannot be torn easily. The insulating layer of high-quality wires has a certain flame retardancy. Peel off a section of the national standard wire insulation layer and ignite it with a lighter. After leaving the open flame, it can self-extinguish, and the smoke is light and has a light smell.

The insulating layer of inferior non-standard wire is made of recycled plastic, which has poor insulating ability, which can easily cause the insulating layer to be broken down by current and leak. Great harm to the life safety of users! Inferior wires can be distinguished from the insulating layer with a little attention. Pull off a section of the insulating layer. As shown in the figure below, if the color of the cross section is white, it is the inferior wire. Fold a certain part of the wire several times in succession. If the color of the folded part turns white, it can be judged. It is a low-quality wire. Use a lighter to carry out the igniting experiment, it can still burn after leaving the open flame, and the smoke has a strong smell. Cut a section of the wire insulation layer to see if there are visible pores in the section of the insulation layer and whether the core is located in the middle of the insulation layer. What is not in the center is the eccentricity caused by the low craftsmanship. The presence of pores indicates that the wire insulation material used is unqualified. Severe eccentricity is most likely to leak electricity on the thinner side, and air holes also affect the compressive strength of the wire.