Wire and cable common sense questions and answers

1. What are the requirements for cable piping?

Answer: (1) The distance from the top of the pipe to the ground is 0.2m in the workshop, 0.5m under the sidewalk, and 0.7m in general areas;

(2) Pipe pits should be installed at the change direction and branch, and pits should also be added when the length exceeds 30mm;

(3) The pit depth is not less than 0.8m, and the manhole diameter is not less than 0.7mm;

(4) The drain pipe should have a drainage slope of 0.5% to 1% inclined to the pit.

2. What are the requirements for the resistance of the cable conductor connection point?

Answer: The resistance of the connection point is required to be small and stable. The ratio of the resistance of the connection point to the conductor of the same length and the same cross-section should not be greater than 1 for the newly installed terminal head and intermediate head; This ratio should not be greater than 1.2.

3. What requirements should the design of cable joints and intermediate head meet?

Answer: The requirements that should be met are:

(1) High compressive strength and good conductor connection;

(2) High mechanical strength, low medium loss;

(3) Simple structure and strong sealing.

4. What is a cable fault? There are several common types?

Answer: Cable failure refers to the failure of the cable’s insulation breakdown during the preventive test or during the operation, which forces the aerial bundled cable 33-209 standard  to power out due to insulation breakdown, wire burnout, etc. Common faults include ground faults, short-circuit faults, disconnection faults, flashover faults and mixed faults.

5. How to deal with the single-phase ground fault of the cable line?

Answer: Generally speaking, the damage to the cable conductor is only partial. If it is a mechanical damage and the soil near the fault point is relatively dry, local repairs can generally be carried out and a fake connector is added, namely Without sawing the cable core, only the fault point is insulated and sealed.

6. What tests and inspections should be carried out on power cables before laying?

Answer: Before laying, check whether the type, specification and length of the cable meet the requirements and whether there is external force damage. Low-voltage cables use a 1000V megohmmeter to remotely measure the insulation resistance, and the resistance is generally not less than 10MΩ, and high-voltage cables are measured with a 2500V megger. The resistance is generally not less than 400MΩ.

7. What should be paid attention to when laying cables in the main workshop?

Answer: When laying cables in the main factory building, generally pay attention to:

(1) All control cables leading to the centralized control room should be laid overhead;

(2) 6KV cables should be laid in tunnels or pipes, and the high groundwater level can also be laid overhead or pipes;

(3) For 380V cables, tunnels, trenches or pipes should be used when the two ends of the cable are at zero meters. When one end of the equipment is on the top and the other is on the bottom, it can be partially overhead laid. When the local water level is high, it should be overhead.

8. Where are the inner and outer shielding layers of power cables? What material is used? What’s the effect?

Answer: In order to make the insulation layer and the cable conductor have better contact and eliminate the increase in the electric field strength of the conductor surface caused by the unevenness of the conductor surface, the conductor surface is generally covered with an inner shielding layer of metalized paper or semiconductor paper tape. In order to make the insulating layer and the metal sheath have better contact, generally the outer surface of the insulating layer is covered with an outer shielding layer. The material of the outer screen layer is the same as that of the inner screen layer, and sometimes copper tape or braided copper ribbon is tied outside.

9. Briefly describe the composition and performance of epoxy resin compound.

Answer: The epoxy resin compound is composed of epoxy resin added with hardener, filler, toughening agent and diluent. Has the following properties:

(1) Have sufficient mechanical strength;

(2) Excellent electrical performance;

(3) Stable electrical performance;

(4) It has sufficient adhesion to non-ferrous metals;

(5) Good corrosion resistance;

(6) When used outdoors, it is resistant to rain, light, and humidity.

Physical characteristics of aluminum alloy cables

The advantage of aluminum alloy cable over ordinary cables is that under the same volume, the actual weight of aluminum alloy is about one-third of copper. According to this calculation, under the premise of meeting the same electrical conductivity, the length of the aluminum alloy cable with the same weight is twice that of the copper cable. Therefore, the weight of the aluminum alloy cable is about half of the copper cable at the same current carrying capacity. The use of aluminum alloy cables instead of copper cables can reduce the weight of the aerial bundled cable ASTM b231, reduce the installation cost, reduce the wear of the equipment and the cable, and make the installation work easier.

Aluminum alloy power cable is a new type of material power cable created by advanced technologies such as AA-8000 series aluminum alloy material as the conductor, using special pressing technology, annealing treatment, and chain armoring technology.

The difference between aluminum alloy cables and ordinary cables: aluminum alloy cables use AA-8000 series aluminum alloy conductors, while ordinary cables use copper or pure aluminum as cable conductors.

Tensile strength and elongation

Compared with pure aluminum conductors, aluminum alloy conductors have greatly improved tensile strength due to the addition of special ingredients and special processing techniques, and the elongation rate has increased to 30%, making it safer and more reliable to use.

Thermal expansion coefficient

The coefficient of thermal expansion is used to calculate the dimensional change of the material when the temperature changes. The coefficient of thermal expansion of aluminum alloy is equivalent to that of copper. Aluminum connectors have been reliably used for copper and aluminum conductors for many years, and most of the electrical connectors used today are made of aluminum, which is especially suitable for aluminum alloys. So the expansion and contraction of the aluminum alloy conductor and the connector are exactly the same.

Strong weight bearing capacity

Aluminum alloy improves the tensile strength of pure aluminum. Aluminum alloy cables can support a weight of 4000 meters, while copper cables can only support 2750 meters. This advantage is particularly prominent when wiring large-span buildings (such as stadiums).

Armour characteristics

Most commonly used armored aerial bundled cables(abc) b230 standard in China are armored with steel tape, with low security level. When subjected to external destructive forces, their resistance is poor, which is easy to cause breakdown, and the weight is heavy, the installation cost is quite high, and the corrosion resistance is poor. The service life is not long. The metal interlocking armored cable we developed according to American standards uses aluminum alloy tape interlocking armor. The interlocking structure between the layers ensures that the cable can withstand the strong destructive force from the outside, even if the cable is subjected to greater pressure The cable is not easy to be punctured under the impact force, which improves the safety performance. At the same time, the armored structure isolates the cable from the outside world. Even in the event of a fire, the armored layer improves the flame-retardant and fire-resistant level of the cable and reduces the risk of fire. Compared with the steel tape armored structure, the aluminum alloy tape armored structure is lighter in weight and convenient to lay. It can be installed without bridges and can reduce installation costs by 20% to 40%. Different outer sheath layers can be selected according to different places of use, which makes the use of armored cables more extensive.

Talking about the advantages of prefabricated branch cables

With the strong growth of my country’s national economy, the speed of various infrastructure, capital construction, and real estate development has accelerated. It is a historical necessity to use mining aerial bundled cables(abc) as the main supply, distribution, and trunk lines in various buildings and facilities. Therefore, construction units, design units, and construction units are seeking more advanced, more economical, superior performance, less effective space, and shorter construction period power supply construction technology and methods. It is also under such historical environmental conditions that prefabricated branch cables have entered my country’s architectural electrical stage in strides.

1) In the middle and high-rise buildings, prefabricated branch cables can be widely used in various middle and high-rise buildings such as residential buildings, office buildings, office buildings, commercial buildings, teaching buildings, scientific research buildings, etc., as the main and trunk cables for power supply and distribution use;

2) In airports and ports, it is used as the main cable for airport runway lighting, port terminal lighting, and power supply and lighting in building facilities;
3) It can be used as lighting power supply in tunnels; it can be used as lighting and power supply network in mines;
4) In the transformation and construction of urban power grids, as the main, kydl_yyyb trunk line mining cables can be buried or overhead;
5) In the modern standard factory building, it is used as the main and trunk cable for mining;
6) In various buildings, facilities, buildings, halls, halls, venues, and even sports facilities, swimming pools, etc., it can be used as main and trunk mining aerial bundled cables BS 7870.
7) Prefabricated branch cables can be used in various other occasions where mining cables are used, such as main and trunk lines of power systems such as ships and ships.

Pre-branch cables have many advantages:

1) The cost of insulation treatment of branch joints is greatly reduced;
2) On-site construction costs are greatly reduced;
3) On-site construction cycle and time are greatly shortened;
4) Reduced on-site construction personnel and equipment; reduced technical requirements for construction personnel;
5) Not restricted by the space and environmental conditions of the construction site;
6) The insulation performance of the branch connector is consistent with that of the cable body, with superior insulation performance and high reliability;
7) It has higher seismic, waterproof and fire resistance performance;
8) The power supply is safe and reliable, and the one-time effective opening rate can reach 100%;
9) Wide application range, many varieties and specifications;
10) Users can conveniently choose cables of various specifications, models, cross-sections, and lengths as the main and branch cables;
11) It has more intuitive maintenance operability.

Causes of fire accidents on overhead cables

Now the use of Aerial Bundle Cable has become more and more extensive, but with its popularity in the national power supply lines, some of its safety problems have gradually attracted people’s attention, especially in recent years, the  cable fire accidents reminds people to pay more attention to when using this kind of cable. So, what are the causes of fire accidents of overhead cables?

1. The nominal conductor cross section of cable core does not meet the requirements. Generally, the specified nominal interface is larger than the actual cable produced, and the cable whose nominal value deviates from the standard will have larger unit current density. In its working process, the cable is easy to cause fire accident because it can not generate heat normally.

2. (ABC)XLPE  Insulated cable production process is poor. Although not every manufacturer is like this, it is inevitable that some businesses in the market will not operate strictly according to the standards in the process of cable production in order to seek personal interests. Even some businesses will use some low-quality products to make rough, resulting in the final production of the cable because the quality is not up to standard, causing fire in the process of use.

3. The material of the cable is impure or unqualified. The core wire of the cable is generally made of some copper or aluminum conductive materials, and many businesses often use unqualified or insufficient purity materials in the production process, which will lead to the reduction of power due to the presence of more impurities. Therefore, the materials used as core wires must be some high-quality electrolyte materials, mainly copper and aluminum.

4.Improper transportation. Most cables are subject to strict quality inspection before leaving the factory, but in the process of transportation, due to the lack of proper protection measures, it is squeezed and collided, resulting in the damage of insulation layer or the breakage of internal core wire

5. The composition of the insulating material does not meet the requirements or the processing is poor. We know that the outside of the cable is generally wrapped with a kind of insulating material. If the quality of the insulating material is unqualified, it will reduce its own withstand voltage performance in the process of use, and will form unqualified resistance value. In addition, long-term use will also shorten its service life, it is easy to have some short-circuit faults and cause fire.

Basic cable performance test

1. Inspection method
Routine test: It is an experiment conducted by the manufacturer on all finished cables. Its purpose is to check whether the quality of the product meets the requirements of the technical conditions in order to find accidental defects in the manufacturing process. It is a non-destructive experiment, such as the DC resistance of the wire and the insulation resistance time. And withstand voltage test, partial discharge detection, etc.
Type test: It is the manufacturer who regularly conducts comprehensive performance inspection of the product, especially for a new product before it is finalized for mass production, or the structure, material and main process of a product have changed, which may affect the performance of the cable Time. Pass type test: It can be tested whether the product can meet the requirements of operation, and can be compared with the old product. Such as thermal aging performance of insulation and sheath, long-term stability test of power cable, etc.
Acceptance test: It is an acceptance test performed on the cable after the cable is installed and laid in order to check the installation quality and find possible damage during the construction. Such as withstand voltage test after installation.

2. Test items
2.1 Measurement of DC resistance of wires
The conductive core of the wire and cable mainly transmits electric energy or electric signal. The resistance of the wire is the main indicator of its electrical performance. When the AC voltage is applied, the core resistance is larger due to the skin effect and the adjacent effect surface than when the DC voltage is applied, but the difference between the two is very small when the electric eye frequency is 50Hz. The current standard stipulates That can only require the detection of whether the DC resistance or resistivity of the core exceeds the value specified in the standard. Through this inspection, certain defects in the production process can be found: such as wire breakage or partial single wire breakage; Meet the standard; the length of the product is incorrect, etc. For aerial bundled cables 1418 standard, you can also check whether it will affect the allowable current carrying capacity of wire and cable products during operation.
There are single-arm DC resistance method and double-arm DC bridge method to measure the DC resistance of conductors. The accuracy of the latter is higher than that of the former. The test procedure is also more complicated than the former.

2.2 Test of insulation resistance
Insulation resistance is an important indicator reflecting the insulation characteristics of wire and cable products. It is closely related to the product’s electrical strength, dielectric loss, and the gradual deterioration of insulating materials under working conditions. For communication cables, low insulation resistance between wires will also increase loop attenuation, crosstalk between loops, and long-distance power supply leakage on conductive cores. Therefore, insulation resistance should be higher than the specified value.
Defects in the process can be found by measuring the insulation resistance, such as the insulation is dry and impermeable or the sheath is damaged and damp; the insulation is contaminated and conductive impurities are mixed in; the insulation layer is cracked due to various reasons. In the operation of aerial bundled cables(abc) sans1418, the insulation resistance and leakage current are often tested as the main basis for continued safe operation.
At present, in addition to the ohmmeter (shaking meter), the current measurement of the insulation resistance of wires and cables is the galvanometer comparison method and the high resistance meter method (voltage-current method).

How to identify poor quality Aerial Bundled Cable

1. Look closely at the label printing, the handwriting is blurred and the address is unknown. It means to look at the printed words on the label and the insulating skin. If there are typos, or the printing is of different shades, or the words are blurred, pay attention to it.
2. Use your fingernails to mark and flick the line , and the line will be cut off. Refers to the use of nails to scratch and pinch the insulating skin. The ones that can be scratched or pinched are generally inferior threads.

3.Twist the insulation skin with your hands, and the color will fade and the characters will be of poor quality. Refers to rubbing the insulating sheath with your fingers. Some inferior insulated wires are easy to fade, especially the red wire. This problem occurs. After rubbing, the color of the thread is left on the finger or the words printed on the thread are wiped off Generally inferior quality Aerial Bundled Cable

4. Repeatedly bend the insulated wire and break (ABC)SANS 1418 Standard three to four times. Refers to repeated bending of insulated wires. Inferior wires are generally of poor quality, and the insulation layer will break after bending 3 to 4 times.

 

5. Use fire to ignite the wire insulation and spontaneously ignite away from the open flame. It refers to the inferior wire that ignites the insulating layer and can ignite spontaneously after leaving the open flame.

6. ​​Aluminum and copper are commonly used for wire cores, and the color becomes darker and lighter. It means to look at the color of the core, the color of inferior thread is gray and without metallic luster.

7, finely measure the inner diameter and outer diameter, and look at the pine when weighing. It means that if it is not determined by the above 6 methods, the outer diameter and core diameter of the insulated wire can also be measured. The allowable error is ±10%. If the measured value exceeds the allowable error, it is basically a low-quality insulated wire.

Selection of cables in normal operation of the wiring system

The entry test of the wiring system is mainly divided into aerial bundled cable(abc) astm b230 test, jumper test, module test and external crosstalk test. Module testing is currently mainly used in laboratory technology models due to its complex technology, mainly facing manufacturers of wiring systems, while the other three are common approach testing techniques for wiring systems.

So how to check these factors qualitatively and quantitatively before construction? The following article will be divided into cable test, jumper test and alien crosstalk test to do a detailed introduction.

1. Pre-construction test: FCL cable test

At present, most data center cabling systems are composed of optical fiber and twisted pair. Optical fiber is mainly used to connect storage devices and servers; twisted pair cables are mainly used for physical connection with switching devices and servers and interconnection of switching devices.

The use of twisted pair cables accounts for 70% to 80% of data center cabling systems. The quality of the twisted pair itself directly affects the quality of the data center cabling system. Ensuring the quality of the twisted pair is the key to improving the quality of the cabling system.

Taking into account the requirements of the data center transmission rate, most of the first parties will require the project implementation party to use well-known brands or cables with good reputation on the market. However, the market is full of aerial bundled cables b230 of various brands, the price gap is very large, and the quality is also far behind. When customers order twisted pair cables, this situation often occurs. The customer requires a certain brand of cable, and the merchant often asks which brand of cable is needed: the quality is average, the better or the best? The best is of course the most expensive, and most likely to be a real brand line.

If the quality is average or better, it may be imitated by some small domestic factories. Although the core technology of twisted-pair cable is in the hands of some large manufacturers, imitation is easy to achieve only from the basic appearance of the cable. If it is not for professionals, it is difficult to see the difference between large-brand products and fake cables in appearance. It is also one of the reasons for the proliferation of false lines. A large part of the price difference is the use of materials. In order to save material costs, many informal manufacturers will add some aluminum and iron to the copper core.

The addition of some other cheap metals such as aluminum makes the transmission of high-frequency signals a big obstacle, especially affecting the transmission rate. There are also some technological differences. For example, the twisted pair has 4 pairs of cores. In order to reduce the crosstalk between each other and balance the interference between the pairs, it is required that the pitch of each pair of cores is not consistent. The higher the frequency of transmission, the greater the mutual interference between pairs. The twisting rate of twisted pair cables of different levels is completely different, and this technology is also one of the core technologies of well-known wiring production brands.

The so-called “general certain brand”, “better certain brand” or “real brand line” can not be judged by the naked eye when customers purchase cables. Due to the lack of understanding of the wiring market or the asymmetry of information, Party A cannot know the quality of the abc cables used before installation.

Therefore, there will be some bad party B winning the bid at a low price, and at the same time using some fake brand-name cables in order to maximize profits. Therefore, Party A needs some effective means to supervise Party B, and Party B also needs to prove the quality of the materials used by Party A.

 

Analysis and Engineering Application of Fireproof Performance of Mine Cable

Due to the increase of wires and cables, the concentration of laying, the poor quality of construction, etc., the danger of wire and cable fires has increased. Therefore, to prevent aerial bundled cable astm b231 fires in actual engineering applications, it is necessary to start with controlling dangerous factors, apply relevant regulations, and take corresponding fire prevention measures.

1 Fire causes and characteristics of wires and cables

Mainly because of overload, short circuit, excessive contact resistance and external heat source. Causes of fire caused by wires and cables under fault conditions such as short circuit, local overheating and external heat. Insulation materials decrease in insulation resistance, lose insulation ability, or even burn, which may cause a fire. The main characteristics of wires and cables in fire are:

In case of fire, the fire temperature is generally 800℃~1000℃. Wires and cables will quickly lose their insulating ability, which will cause secondary electrical accidents such as short circuits and cause greater losses;

2 The conductor cable has a larger overload capacity under the specified allowable current carrying capacity;

The wire and cable will cause the insulation material to melt and burn in an instant, 3 short-circuit conditions. And ignite the surrounding combustible materials.

2 Analysis of fire performance of aerial bundled cable (abc) astm b231 standard 

2.1 Analysis of fire protection mechanism

2.1.1 Flame retardant mechanism

The flame retardant in the condensed phase decomposes and absorbs heat, and is under the heat of the combustion reaction. Slow down the temperature rise in the condensed phase and delay the thermal decomposition rate of the material;

The chain reaction free radical blocker is released, and the flame retardant is decomposed by heat. Interrupt the branches of flame and chain reaction, and slow down the speed of gas phase reaction;

The formation of the coking layer or foam layer strengthens the effect of these layered hard shells in hindering heat transfer; 3 catalyzes the thermal decomposition of the solid phase products of the condensed phase.

The flame retardant has an endothermic phase change, under the action of 4 heat. Physically prevent the temperature rise in the condensed phase.

2.1.2 Fire resistance mechanism

To reduce the heat generated by the polymer, a certain additive is added to the insulation and sheath materials of the wire and cable. Prevent polymer decomposition or promote the carbonization of insulation and sheath materials to form a maintenance layer;

After the insulation and sheath layer is eroded by fire, a layer of mica glass ribbon and other inorganic insulating materials are added to the 2 cores. *The mica refractory tape wrapped around the conductor is maintained and continues to be energized, so as to maintain normal operation for a certain period of time when a fire occurs.

2.1.3 Mechanism of mineral insulated cables

AlOH3 is 34.6% under high temperature operation, and the absorption effect of metal hydrate makes the cable flame-retardant. For example: use AlOH3 and MgOH as flame retardants. MgOHz is 31%, see Reaction Equation 1 and Reaction Equation 2, the reaction is decomposed into an endothermic reaction, which can inhibit the burning of polymers. 2A IOH3–*A lz03+3H20-2648KJ1MgOH2–MgO+H20-93.3KJ2

2.2 Classification of burning characteristics of wires and cables and their standard tests

It can be divided into ordinary wire and cable, flame-retardant wire and cable, fire-resistant wire and cable, halogen-free low-smoke wire and cable, and mineral insulated cable. Wire and cable according to their own burning characteristics.

1 Flame-retardant wires and cables refer to wires and abc cables b230 that are difficult to catch fire and have the ability to prevent or delay the spread of flame. The commonly used standard test is GBT18380. 3 is equivalent to IEC60332-1999

Wire and cable that can still maintain the integrity of the circuit. The commonly used standard test is GBT12666. 6 which is equivalent to IEC60331-21-19992 fire-resistant wire and cable means that it burns under a flame at a specified temperature and time.

When burning, it produces less smoke and has wires and cables that prevent or delay the spread of flames. Commonly used standard tests are GBT17650. 2 is equivalent to IEC60754-2, GBT17651. 2 is equivalent to IEC61034-2 and GBT18380. 3 is equivalent to EC60332-3. On the basis of the above, the flame-retardant and fire-resistant type also need to meet the requirements of maintaining the integrity of the line. 3 There are two types of halogen-free and low-smoke wires and cables. Flame-retardant type means that the material does not contain halogen. At the same time, the commonly used standard test adds GBT12666. 6 is equivalent to IEC60331

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.

The advantages of copper core cable and aluminum core cable are compared

Copper core cables have more advantages than aluminum core cables:

1. Low resistivity: the resistivity of aluminum core aerial bundled cable BS 7870 is about 1.68 times higher than that of copper core cable.

2. Good ductility: the ductility of copper alloy is 20-40%, the ductility of electrical copper is more than 30%, while aluminum alloy is only 18%.

3. High strength: the allowable stress at room temperature, copper is 7~28% higher than aluminum. Especially the stress at high temperature, the difference between the two is even greater.

4. Anti-fatigue: Aluminum is easy to break after repeated bending, while copper is not easy. In terms of elasticity index, copper is also about 1.7-1.8 times higher than aluminum.

5. Good stability and corrosion resistance: The copper core is resistant to oxidation and corrosion, while the aluminum core is susceptible to oxidation and corrosion.

6. Large current carrying capacity: Due to the low resistivity, the copper core cable of the same cross section is about 30% higher than the allowable current carrying capacity (the maximum current that can pass) of the aluminum core cable.

7. Low voltage loss: Due to the low resistivity of the copper core cable, the same current flows in the same section. The voltage drop of the copper core cable is small. Therefore, the same transmission distance can ensure higher voltage quality; in other words, under the allowable voltage drop condition, the copper core cable can reach a longer distance, that is, the power supply coverage area is large, which is beneficial to network planning and reduces The number of power supply points.

8. Low heating temperature: Under the same current, the copper core cable with the same cross section has much smaller heat than the aluminum core cable, which makes the operation safer.

9. Low energy consumption: Due to the low electrical resistivity of copper, it is obvious that copper cables have low power loss compared to aluminum cables. This is conducive to improving the utilization rate of power generation and protecting the environment.

10. Anti-oxidation and corrosion resistance: The performance of the connector of the copper aerial bundled cable(ABC) B231 is stable, and there will be no accidents due to oxidation. When the connector of aluminum core cable is unstable, the contact resistance will increase due to oxidation and heat will cause accidents. Therefore, the accident rate is much greater than that of copper core cables.

11. Convenient construction: The copper core is flexible and the allowable bend radius is small, so it is convenient to bend and easy to pass through; the copper core is fatigue-resistant, repeated bending is not easy to break, so the wiring is convenient; the copper core has high mechanical strength and can withstand relatively The large mechanical pulling force brings great convenience to construction and laying, and also creates conditions for mechanized construction.

12. Cheap price: Copper pole is 3.5 times the price of aluminum pole, and the proportion of copper is 3.3 times that of aluminum. Therefore, aluminum core cables are much cheaper than copper core cables, and are suitable for low-cost projects or temporary electricity use.

13. The cable is very light: the weight of the aluminum core cable is 40% of the copper core cable, and the construction and transportation costs are low.

14. Anti-oxidation and corrosion resistance: Aluminum quickly reacts with oxygen in the air to form an oxide film, which can prevent further oxidation. Therefore, aluminum wire is a necessary material for high-voltage, large-section, and large-span overhead power transmission.

Although aluminum core cables are cheap, copper cables have outstanding advantages in cable power supply, especially in the field of underground cable power supply. The underground power supply using copper core cables has the characteristics of low accident rate, corrosion resistance, high reliability, and convenient construction and maintenance. This is why copper abc cables are mainly used in underground power supply in China.