Why measure the surface temperature of the cable in operation?

The temperature of the cable is closely related to the load, but only checking the load can not ensure that the AAAC Cable is not overheated
(1) the thermal resistance coefficient and side-by-side correction coefficient used in calculating the allowable ampacity of cables may be different from the actual situation.
(2) when choosing cables to determine conductor cross-sectional area, designers may lack sufficient information about the laying conditions and surrounding environment of the whole line.
(3) newly built and rebuilt power lines or thermal pipelines have an impact on the original surrounding environment and heat dissipation conditions.


(4) the excessive density of cables greatly exceeds the regulations of design and operation departments. In addition to measuring the load frequently, the operation Department must also check the actual temperature of the cable surface to determine whether the AAC Cable is overheated. The inspection shall be carried out at the maximum load and the section with the worst heat dissipation condition (generally not less than 10m). Thermocouple or pressure thermometer can be used for measuring instrument. The pressure thermometer is easy to install. Two temperature measuring points shall be installed at each measuring point. When measuring the temperature of the cable, the temperature of the surrounding environment should be measured at the same time, but it must be noted that the temperature measuring point of the surrounding environment should be kept a certain distance from the cable (generally 3M away), and there is no influence of external heat source.
On site detection method
During infrared detection, the cable should be live running for more than 24 hours, and try to remove or avoid the shelter between the cable and the thermometer, such as glass window, door or cover plate, etc; It is necessary to measure all parts of the cable line to avoid missing the measuring parts; It is best to carry out the test in the peak load state of the equipment, generally no less than 30% of the rated load. The infrared detection of the arrester connected with the cable terminal can refer to the requirements of DL / t664.
a) The emissivity of the tested equipment should be selected correctly, especially considering the influence of metal material oxidation on the selection of emissivity. For the selection of emissivity, please refer to Appendix B; Generally, 0.9 for metal conductor and 0.92 for insulator;


b) If the safety distance is allowed, the infrared instrument should be close to the equipment under test as far as possible, so that the equipment under test can fill the field of view of the whole instrument, so as to improve the resolution and temperature measurement accuracy of the instrument to the surface details of the equipment under test. If necessary, medium and long focal length lenses should be used; Generally, medium and long focal length lenses are used for outdoor terminal detection;
c) The compensation parameters such as atmospheric temperature, relative humidity and measurement distance are input and corrected, and the appropriate temperature range is selected;
d) Generally, the infrared thermal imager is used to scan all the tested parts, focusing on the cable terminal and intermediate connector, cross interconnect box, grounding box, metal sleeve grounding point and other parts. After finding the abnormal parts of the thermal image, the abnormal parts and the key tested equipment are measured in detail;
e) In order to measure temperature accurately or track conveniently, several different directions and angles should be set in advance to determine the best detection position and mark it for future retest, so as to improve the comparability and work efficiency;
f) Record the actual load current and voltage of the tested equipment, the temperature of the tested object and the temperature value of the environmental reference body according to the format of Appendix C.

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Choose the wire and cable, quickly identify the type!

The main function of wire and cable is to transmit electric energy, signal and realize electromagnetic conversion. The transmission of electric power, such as power cable, overhead line, etc., is the same as shaft ABC Cable, and the wire with electromagnetic conversion is like paint wrapped wire. If you choose a wire or cable, you need to quickly identify the type and type to select the right cable to use.

According to the number of transmission lines of each other with each other which are fixed together, the insulated wires can be divided into single core wires and multi-core wires. Multi core wires can also fix multiple single core wires in one insulating sheath. The multi-core wires in the same sheath can be as many as 24 cores. The parallel multi-core line is indicated by “B”, and the twisted multi-core wire is indicated by “s”.
Insulated wires can be divided into single wire and multi-core wire according to the stock number of each transmission line. Generally, the insulated wires above 6 square mm are all multi-core wires. The insulated wires with 6 square mm and below can be single wires and can also be multi-core wires. We call the single wire of 6 square mm and the following as hard wire, and multi-core wire is called copper wire.
Hard wire is indicated by “B” and copper wire is indicated by “R”. The common insulating materials of ACSR Cable are polyethylene and high pressure polyethylene. The “V” of PE indicates that “Y” is used for high-pressure polyethylene.

Bv copper core polyethylene insulated wire; BLV aluminum core polyethylene insulated wire; BVV copper core polyethylene insulation layer polyethylene protective cable; Blvv aluminum core polyethylene insulation layer polyethylene protective cable; BVR copper core polyethylene insulation copper wire;
RV copper core polyethylene insulation layer is installed with copper wire; RVB copper core polyethylene insulation layer flat electrode connecting wire copper wire; BVS copper core polyethylene insulation layer twisted copper wire; RVV copper core polyethylene insulation layer polyethylene wire sheath copper wire;
BYR high voltage polyethylene insulated soft cable; Byvr high voltage polyethylene insulation layer polyethylene wire sheath copper wire; Ry high voltage polyethylene insulated copper wire; RYV high voltage polyethylene insulation layer polyethylene wire sheath copper wire;
BVVB copper core polyethylene insulation layer polyethylene protective wire sleeve flat cable; BLVVB aluminum core polyethylene insulation layer polyethylene protective wire sleeve flat cable; Bv-105 copper core high temperature resistant 105 ℃ polyethylene insulated wire.

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What are the three rules for selecting wires and cables

The application of wire and cable in life is essential. What people pay more attention to is the quality of wires and cables, but the types of cables are also various. The more kinds, the more difficult it is to choose. Many people don’t know how to choose the right wires and cables to use, which leads to problems. To teach you how to choose the right wires and cables
Nowadays, more and more ACSR Cable lines are used in distribution lines, but it is very important to choose the cable type. Combined with the actual work, the paper simply discusses the application scope and selection of 10kV cable lines. First, it is necessary to determine where the cable is applied, where the cable passes, the load nature, capacity, etc. to select the cable.

1、 Application scope of wire and cable line: the place where the power equipment is clustered, prosperous area, important section, major roads, urban planning and urban environment with special requirements. In the area of serious pollution and corrosion which is difficult to solve, the reliability of power supply is high or the users with important load are required, key scenic spots, high load density urban center areas, new residential areas and high-rise buildings with large building area are built.
2、 Selection of wires and cables: determine the section according to the long-term allowable current carrying capacity, select the cable section according to short circuit thermal stability, select the cable section according to the voltage drop of the connecting circuit, check the section according to the mechanical strength, and select the section of neutral wire (n), protective ground wire (PE), protective grounding neutral line (pen).


3、 Correction of the current carrying capacity of electric wires and cables: long-term allowable current carrying temperature correction of cables, soil correction of long-term allowable current carrying capacity of cables, long-term allowable current carrying capacity correction for directly buried and parallel laying power cables, and correction of carrying capacity of 10kV and below cables laying through pipes.ç

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How to select cable label

AAAC Cable label is an identification mark used in field installation and after maintenance.
The purpose of cable identification is
Ensure the organization and correctness of installation
And the convenience of maintenance and inspection later.
This paper is to share the purpose, characteristics and how to choose cable label for you.

Application and characteristics of cable identification
In a line system, it is impossible for the operation and maintenance personnel to memorize a wide range of equipment and lines. In order to make sure that they do not miss in the inspection, it is necessary to manage the line identification. After marking each line, it shall be sorted and summarized and posted in a conspicuous position. In the future, it can be done without omission if the inspection is carried out in strict accordance with the project requirements.
Cable identification system can not only provide correct guarantee for the operation and maintenance personnel to carry out correct daily maintenance and abnormal accident handling, but also provide help for the later generations. Even if the new personnel are employed, as long as the identification is followed, there will be no misoperation.
How to select ACSR Cable label
Mark before or after the terminal is completed
Cable identification card: 1. It can be used before or after the terminal connection. 2. The content is clear. The label is completely wrapped around the cable.
Heat shrinkable cable identification pipe: 1. It can only be used before the terminal is connected, and is sheathed on the wire through the open end of the wire. 2. Before heat shrinking or splicing, the label can be replaced randomly. 3. After the terminal is jacketed, the sleeve will become a permanent mark which can withstand the bad environment. And it’s low cost.
What is the diameter of the cable
The diameter of the cable determines the type, length, or diameter of the sleeve to be identified. Cable identification card is widely used in large square cable, large logarithmic cable and outdoor optical cable. The heat shrinkable label tube is widely used on the small square secondary small line. Identification cards can be used for various cables of different diameters.
What environment will cable labels be placed in
Factors to consider include:
1. Is there any contact with oil, water, chemicals or solvents?
2. Is flame retardant required?
3. Does the state have any special or other provisions on this?
4. Is it used in clean or other environments? Even in the harsh environment, the heat transfer printing, industrial grade printing quality, has strong anti pollution, in fact, the print content is also “anti oil pollution”.

Do you plan to print or buy pre processed logo yourself?
Purchase cable identification
1. There are a variety of preprint content available for selection;
2. If the demand is large, it can provide customized preprint content;
3. There are various kinds of marks such as card and sleeve type, which can be selected, convenient to use and convenient for transportation;
4. It is suitable for various applications.
Print logo by yourself
1. Print various content as needed (even if you print very little);
2. There are various label and label sleeve materials for portable printer, heat transfer printer and computer printer;
3. Suitable for printing longer characters;
4. And have the label size suitable for different applications.

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Cable fault detection and search method, you should understand

For direct short circuit or broken cable fault, the multimeter can be used to measure and judge directly; For non direct short circuit cable fault and grounding AAC Cable fault, the insulation resistance between cores or insulation resistance between cores to ground can be measured by megohmmeter, and the type of cable fault can be judged according to the resistance value. The following describes the method of cable fault finding:
Zero potential method
The zero potential method is also called potential comparison method. It is suitable for short cable core to ground fault. The application of this method is simple and accurate, and does not need precise instruments and complicated calculation. The measurement principle is as follows: parallel the cable fault core with the same length of comparison wire, when the voltage VE is applied at both ends of B and C, it is equivalent to connecting the power supply at both ends of two parallel uniform resistance wires. At this time, the potential difference between any point on one resistance wire and the corresponding point on the other resistance wire must be zero, otherwise, the two points with zero potential difference must be the corresponding points. Because the negative pole of the microvolt meter is grounded and equipotential with the cable fault point, the point when the positive pole of the microvolt meter moves to zero on the comparison wire is equipotential with the cable fault point, that is, the corresponding point of the cable fault point. S is a single-phase knife switch, e is a 6e battery or four No. 1 dry batteries, and G is a DC microvolt meter
1) First, connect battery e to B and C phase core wires, and then lay a comparison wire s with the same length as the fault cable on the ground. The wire shall be bare copper wire or bare aluminum wire with equal cross section and no intermediate joint.
2) The negative pole of the microvolt meter shall be grounded, and the positive pole shall be connected with a long flexible wire. The other end of the wire shall be fully contacted when sliding on the laid comparison wire.
3) Close the knife switch s, slide the end of the flexible wire on the comparison wire, and the position when the microvolt meter indicates zero is the position of the ACSR Cable fault point.


High voltage bridge method
High voltage bridge method is to measure the DC resistance value of the cable core with double arm bridge, and then accurately measure the actual length of the cable, and calculate the cable fault point according to the positive proportional relationship between the cable length and resistance. This method is suitable for direct short circuit between cable cores or short circuit point contact resistance less than 1 Ω Generally, the judgment error is not more than 3m, and the contact resistance is greater than 1 Ω The method of high voltage burn through can be used to reduce the resistance to 1 Ω Next, measure according to this method. When measuring the circuit, first measure the resistance R1 between core a and B, R1 = 2RX + R, where Rx is the resistance value of a phase or B phase to the cable fault point, only the contact resistance of short contact. Then move the bridge to the other end of the cable and measure the DC resistance value R2 between A1 and B1 core wire, then R2 = 2R (l-x) r, R (l-x) is the resistance value of one phase from A1 phase or B1 phase core wire to the cable fault point. After measuring R1 and R2, short circuit B1 and C1 according to the circuit shown in Fig. 3, and measure the DC resistance value between B and C two-phase core wires, then 1 / 2 of the organization is the resistance value of each phase core wire, expressed by RL, RL = RX R (l-x), from which the contact resistance value of the fault point can be obtained: r = R1 r2-2rl table. Therefore, the resistance value of core wires on both sides of the fault point can be expressed by the following formula: RX = (r1-r) / 2, R(L-X)=(R2-R)/2。 After Rx, R (l-x) and RL are determined, the distance X or (l-x): x = (Rx / RL) l, (l-x) = (R (L-2) at the end of the cable, the capacitance current IA1, IB2 and IC3 of each phase core are measured to check the capacitance ratio between the core and the broken core, and the approximate point of the broken distance can be judged preliminarily.
3) According to the capacitance calculation formula C = I / (2) Π When the positive voltage U and frequency f are constant, C is proportional to I. Because f (frequency) of power frequency voltage is constant, the ratio of capacitance current is the ratio of capacitance as long as the applied voltage is constant. If the total length of the cable is l and the distance between the broken point of the core is x, then IA / ic = L / X and x = (IC / IA) L. In the process of measurement, as long as the voltage remains unchanged, the reading of ammeter is accurate and the total length of cable is accurate, the measurement error is relatively small.
Sound measurement
The so-called sound measurement method is based on the sound of fault cable discharge, which is more effective for the flashover discharge of high voltage cable core to insulation layer. The equipment used in this method is DC withstand voltage testing machine. TB is the high voltage test transformer, C is the high voltage capacitor, VE is the high voltage rectifier silicon stack, R is the current limiting resistance, q is the discharge ball gap, l is the cable core. When the capacitor C is charged to a certain voltage value, the ball gap discharges the cable fault core wire, and the cable core wire discharges the insulation layer at the cable fault location, producing “Zi, Zi” spark discharge sound. For the open laying cable, it can be found directly by hearing. If it is buried cable, it is necessary to determine and mark the cable direction first. When searching, put the pickup close to the ground and move slowly along the direction of the cable. When the “Zi, Zi” discharge sound is the largest, this is the cable fault point. It is necessary to pay attention to safety when using this method, and special personnel should be set up at the end of test equipment and cable. The cable fault locator produced by our company can not only measure the sound, but also detect the magnetic signal. The signal strength is visually displayed synchronously, which can locate the cable fault point faster and more accurately.

Discussion of the cable production process: conductor stranding

Discussion on the cable production process: conductor twisting and twisting
: the process of twisting many small diameter monofilaments into a large cross-section conductive core according to certain rules.
1. There are two types of twisted wires: normal twisted wires and irregular twisted AAC Cables.
Ordinary strands can be divided into ordinary concentric single stranded strands and ordinary concentric single stranded strands
(1) Ordinary stranded wire: single wires of the same diameter are twisted layer by layer according to concentric circles, and the direction of each layer is opposite.
(2) Combined stranded wire: made of a single wire of the same diameter, different materials or different diameters and different materials (representative products (such as overhead conductors))
Ordinary concentric stranded wire: a multi-stranded ordinary stranded wire or bundle Stranded wire concentrically stranded.
Irregular stranding (strand): strands formed by multiple single strands in the same direction, which does not comply with the law of twisting. The positions of the single strands are not fixed to each other, and the shape of the strands is difficult to maintain Round.

2. The biggest difference between the bundle wire and the ordinary stranded wire is that each single wire of the ordinary stranded wire has a fixed position and is regularly twisted layer by layer. There is no fixed position between the single wires of the bundle According to the law of twisting, the position will not be twisted together.
3. The characteristics of irregular twisting (bundling) : Since each single wire in the bundle is twisted in one direction, there is a residual amount of sliding between each single wire during bending. The amount is large and the bending resistance is small, so the bending performance of the bundle is particularly good. For wire and cable products that need to be flexible and frequently moved, the wire bundle is used as the conductor core.
4. The characteristics of the stranded core:
(1) Flexibility Good; by using a core composed of several single wires with smaller diameters, the bending resistance of the cable can be improved, and the processing, manufacturing, installation and laying of the wires and cables are convenient.
(2) Good stability; the core is It is composed of multiple single wires twisted according to a certain direction and twisting rules, because each single stranded wire is located in the stretched area above the twisted wire in the twisted wire, and is located in the lower compressed area When the stranded wire is bent in sequence, the stranded wire will not be deformed.
(3) Good reliability; due to material inhomogeneity or defects in twisting, using a single wire as the cable and the conductor of the cable easily affects the reliability of the conductor core. The defects of the conductor core formed by multiple single wires are scattered and will not be concentrated on a certain point of the conductor, so the reliability of the conductor core is much stronger.
(4) High strength; the strength of the single-stranded core is higher than that of the single-stranded core.

5. Explanation of terms:
(1) Pitch: the distance that a single filament advances one circle along the axis.
(2) Pitch diameter ratio: the ratio of the pitch length to the strand diameter.
(3) The relationship between the pitch and the flexibility of the strands: the smaller the pitch, the better the flexibility of the strands; on the contrary, the larger the spacing, the worse the flexibility of the strands.
(4) Stranding factor: the ratio of the actual length of a single wire to the pitch length in the pitch of the twisted wire.
(5) Twisting direction of the stranded wire: right direction (z direction) left direction (s direction)
(6) Compact conductor: common compact conductors are compact round, sector and compact tile-shaped (five-core cables) Semi-circular (two-core cable)
6. Compression purpose:
(1) Compact sector conductor: reduce the outer diameter of the cable, save product costs, and reduce the weight of the cable.
(2) Compact circular conductor: Improve the surface quality of the stranded conductor, reduce the diameter of the conductor, and increase the filling factor of the conductor. The compacted conductor surface is smooth without burrs, and the electric field on the conductor surface is uniform. Save materials and reduce costs (to learn more about cable technology, please click here. A lot of dry goods are waiting for your visit.)
7. Conductor classification:
According to GB/t3956 “Cable Conductor”, there are four types of conductors, namely the first One, the second, the fifth and the sixth. The first is a solid conductor, and the second is a stranded conductor, both of which are suitable for fixed laying of cables. The fifth and sixth types are stranded conductors, which are used for flexible cables and cords. The sixth is softer than the fifth.
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Discussion on cable process: cable forming

1、 What is cable formation
Definition of cable forming: the process of twisting multiple insulated cores into AAC Cables according to certain rules.
2、 The role of cable forming in cable production
Cable forming is one of the important processes in the production of multi-core cables. The three core, four core (one core is the ground wire) and five core (one core is the ground wire and the other is the neutral wire) of the three-phase power supply is commonly used for power cables. The number of control cable cores is more (more than 2 cores to 61 cores). During the cable forming process, several insulated cores are twisted together according to certain rules, The process of forming a multi-core cable. In addition to the stranding, the process of cable forming includes filling of the gap between the cores of the insulated wires, wrapping and shielding on the core after the cable forming.
When forming cables, the twisted form of insulation core adopts concentric normal stranding. If the diameter of the insulated core is identical, it is called symmetrical cable forming. If the diameter of the insulation core is different, the cable formation is called asymmetric cable formation. In order to avoid the influence of torsional stress on the core during the process of cable forming, the cable forming machine with the torsion device or bow shaped cable forming machine is used for the cable forming of circular insulated core to conduct the twisting and twisting.
3、 The way of cable forming
There are two ways to twist the strand and the cable, one is to twist back and the other is not to twist.
The rewinding and twisting is that the cable tray frame equipped with the setting out plate keeps the setting out plate at all times horizontal position when the machine rotates by means of the special device (the torsion device) on it. When the cable is formed, the insulation core is only subjected to the bending action, but does not twist. The back twisting is often used in the process of forming the circular insulated core. The core has no rebound stress after the cable forming, which can ensure the accuracy of the roundness and diameter of the cable.
The non twisted twisted cable is mostly used for the formation of fan-shaped lines. After the compression of the die, it becomes plastic deformation, thus eliminating the original torsional stress and ensuring the round after the cable is formed.


4、 Cable forming direction and pitch diameter ratio

The cable forming direction is generally right. The confirmation of cable forming direction is in the direction of ACSR Cable core forward, if the cage turns left, it is right direction, otherwise, otherwise, it is opposite.
The ratio of cable pitch diameter is different according to different types of cables. The circular core insulated by cross-linked polyethylene is hard and the diameter of cable forming is larger, with a disk of 30-40; The pitch diameter ratio of PVC insulated power cable is 30-40, and that of sector line is 40-50; The diameter ratio of the cable core of plastic insulated control cable is specified in the national standard, and generally it shall not be more than 16-20.
5、 Stranding coefficient and twist rate
In a pitch of the cable forming, the ratio of the actual length of the insulation core to the length of the pitch of the cable is called the stranding coefficient (k=l/h);
The stranding rate is the ratio between the difference between the actual length of the insulating core and the length of the cable forming pitch and the length of the formed pitch within a cable forming pitch λ=( L-H)/H × 100%
It is convenient to adopt the coefficient K, and the K value is always greater than 1. Thus, the actual value of K is increased by one K value for the single insulated core after the cable forming. The resistance of the core is proportional to the core, that is, the resistance of the core is also increased by a k value. If the insulation resistance is inversely proportional to the length of the insulating core, the insulation resistance of each core will be reduced by a k value. From the angle of reducing the core resistance and increasing the insulation resistance value, it is hoped that the smaller the coefficient of cable winding is, the better.
The ratio of the cable formation to pitch ratio is inversely proportional to the square of the pitch ratio. Therefore, the smaller the pitch ratio, the greater the coefficient of the cable formation, the greater the amount of insulating core material is, otherwise, from the perspective of saving the material consumption, the smaller the coefficient of cable formation is, the better.
6、 Wrapping process
The production process of wrapping all kinds of metal or non-metallic materials on the core or core of the guide cable is covered with the specified pitch spiral in the form of ribbon or wire.
7、 Non armored cable wrapping
In order to prevent the cable core from deformation after the cable forming and to prevent the adhesion with sheath, the insulating core shall be wound with the wrapping layer while forming and filling on the cable forming machine. For the non armored plastic insulated cable, the 1-2-layer non-woven fabric belt is usually wrapped by covering (the first layer or two layers are used for the specific purpose, and the principle of cable forming and tightening is adopted), The covering size is 10% – 15% of the bandwidth, and the wrapping angle is 25% °~ forty ° Within the scope.


8、 Armouring of cables
Steel belt armored cable is mainly suitable for underground direct burial, and can bear certain mechanical pressure; Steel wire armored cable is mainly suitable for laying with drop or vertical, and can bear large mechanical tension. Armored cable is mainly divided into steel strip armor and steel wire armour, and their combination armouring mode.
If there is shielding material (including unified shielding) on the core of the steel belt armored cable, the cable core shall be replaced by the extruded insulating sleeve instead of the inner layer. If the insulation core has no metal shielding layer, the inner layer of the insulation wire can be extruded or wrapped. The inner layer of the wrapping is generally PVC or PE and other similar strip.
Generally, the steel wire armored cable adopts the extruded inner layer.
For the model of armored cable, such as yjv22, there will be two numbers, the first number is the armor Code: generally, there are 2, 3 and 4 numbers:
2 – indicates double layer steel belt armor
3 – indicates the thin steel wire armouring
4 – indicates the thick steel wire armouring
The steel strip thickness and copper clearance of armored cable, wire diameter and clearance of steel wire armored cable shall meet the relevant standards.

Conductor outer diameter in selecting and purchasing wires and cables

With the development of national economy, urban construction is becoming more and more prosperous, and the market demand for decoration cloth and wire products is strong. Cloth and Wire Manufactor products belong to CCC compulsory certification products. Domestic manufacturers implement the national standard GB / T 5023-2008 when producing. Manufacturers must send the products to the designated authoritative testing agency for performance testing every year, It is illegal to obtain the production license by virtue of the inspection report and on-site audit, if the product is produced without the production license.


Through market investigation, when consumers compare products of the same specification in the market, they often find out why the outer diameters of conductors of different manufacturers are different. For example, take the conductor for 6mm2 wiring as an example, the outer diameters of conductors of some manufacturers are 2.76mm, and those of some manufacturers are 2.90mm or even larger, which creates an illusion for consumers, The larger the outer diameter of the conductor, the better the wiring. In fact, it is not. In view of this situation, the following three aspects are discussed:
1. Standards
In the old version of GB / T 5023-1985, the outer diameter and DC resistance of conductor are strictly specified, and the outer diameter of conductor for 6mm2 wire is 2.76mm; In 1997, the new national standard GB / T 5023-1997 for wire laying stipulated that the conductor performance index must meet the requirements of GB / T 3956 (national standard for cable conductor), while the maximum outer diameter of conductor for 6mm2 wire laying should not exceed 2.90mm in GB / T 3956; In the new edition of national standard GB / T 5023-2008, the requirements for outer diameter of conductor are the same as those in GB / T 5023-1997, that is, the maximum outer diameter of conductor for 6mm2 wiring shall not exceed 2.90mm( At present, GB / T 5023-1997 is the latest effective national standard for wiring, which has replaced GB / T 5023-1985 and GB / T 5023-1997
2. Craft
The outer diameter of conductor (2.76mm) is strictly stipulated in GB / T 5023-1985, but the maximum outer diameter of conductor (2.90mm) is only required in GB / T 5023-1997 and GB / T 5023-2008. This is mainly because: in the 1980s, the smelting process level of raw material copper was not high, and there were many impurities in copper rod, which resulted in high conductor resistance, The national standard strictly requires the outer diameter of wire conductor. With the continuous development of copper smelting level and the improvement of conductor processing technology, the impurity content in copper is getting smaller and smaller. At present, in the industry, under the condition of ensuring that the DC resistance of conductor meets the requirements, the outer diameter of conductor produced has been reduced correspondingly, and the consumption of copper has also been reduced correspondingly, This is also the reason why the national standard only specifies the maximum outer diameter of the conductor, but does not specify the specific value of the conductor.

halogen free cable
3. According to the DC resistance formula of Conductor:
R= ρ× L/S
R is the DC resistance of conductor;
ρ In the ambient temperature of 20 ℃ ° Resistivity of conductor at different time
L is the unit length of conductor
S is the cross-sectional area of the conductor
According to the formula, in order to ensure the current carrying capacity of the wire to meet the requirements, the DC resistance of the conductor must meet the requirements of the standard ρ S is related to the diameter of the conductor, ρ When the DC resistance of the conductor is constant, when the outer diameter of the conductor is large, the resistance of the conductor will decrease ρ If the outer diameter of the conductor is small, the copper purity will decrease ρ The purity of copper increases with the decrease of the temperature.
According to the analysis of the above three aspects, when consumers choose wire products, the size of the outer diameter of the wire conductor can not be used as the only standard to judge whether the product is qualified or not, that is, when the wire specifications are selected, the larger the outer diameter of the conductor is, the worse it is. Therefore, the product quality should be judged according to the direct current resistance and mechanical properties of the conductor.

Recommendations for BTLY cable cross-section selection

1. Select the cross section according to the temperature rise of the core
When the load current is passed, the core temperature does not exceed the long-term working temperature allowed by the cable insulation. That is to say, select according to the allowable current-carrying capacity.
Suggestion: The cable passes through different heat dissipation conditions. The corresponding core operating temperature will be different, and the section should be selected according to the area with severe heat dissipation conditions (usually no more than 1 meter).


2. Select the cross section according to the allowable range of voltage loss
When the terminal voltage of the electrical equipment actually deviates from the rated value, its performance will be affected, and the extent of the impact will be determined by the magnitude and duration of the voltage deviation.
Suggestion: The voltage loss increases due to the sharp rise of the core temperature during fire. The voltage loss should be calculated according to the fire conditions to ensure the continuous operation of important equipment. Due to the excellent heat insulation and heat dissipation characteristics of BTLY products, it is only necessary to enlarge the cable selected according to the normal situation by one to two. Usually, it can meet the condition that the voltage deviation under fire conditions is not more than -10%.
Three, select the cross section according to the economic current
The total cost during the economic life is small. That is, the initial investment and the cost of line loss during the economic life are small.
The so-called economic current is the working cable (range) corresponding to the applicable cross-section (range) during the life of the cable, the sum of investment and conductor loss costs. For details, please refer to “Low Voltage Cable Economic Current Density Range Table”.


Suggestion: BTLY products should have good heat dissipation characteristics. If the cross section is selected according to the temperature rise of the core, the selection can be reduced by one level. But taking into account the economic current factor. Therefore, it is not recommended. If selected in accordance with the routine, the line loss will be reduced by 4-7%, which is of great economic significance.
Fourth, the selection of the cross section of the neutral power cable and the ground wire
(1) In a single-phase two-wire circuit, regardless of the size of the phase wire cross section, the neutral wire and ground wire should be the same cross section as the phase wire.
(2) In the three-phase five-wire power distribution system, the allowable current carrying capacity of the neutral wire and ground wire should not be less than the sum of the large unbalanced load current and harmonic current in the line. When the phase wire core is not larger than 16mm2, the neutral wire and ground wire should have the same cross-section as the phase wire. When the phase wire core is larger than 16mm2, if the neutral wire current is small, the cross section of the phase wire can be selected, but it should not be less than 50% of the phase wire cross section and not less than 16mm2.
Suggestion: Use the aluminum metal sheath in the BTLY cable as the grounding core. The aluminum pipe grounding wire is connected by a dedicated connector, and the connection is firm and reliable. The equivalent resistance of the aluminum tube section of the BTLY cable meets the grounding needs of the corresponding copper core

Advantages of BTTZ rigid mineral insulated cable

Due to the special structure of BTTZ rigid mineral insulated cables, it has some characteristics different from traditional cables; it is also the most superior fire resistance characteristic of mineral insulated cables.
Advantages of BTTZ rigid mineral insulated cable
1) Completely fireproof BTTZ cable itself does not burn at all, and it will not cause a fire source at the same time. Even in the case of flame barbecue, as long as the flame temperature is lower than the melting point of copper, the cable can be used without replacement after the flame is eliminated. In the case of being grilled by flames, no toxic smoke and gas will be produced.


2) Strong overload protection capability When the line is overloaded, the cable will not be damaged as long as the heat does not reach the melting point of copper. Even if the breakdown occurs instantaneously, the magnesium oxide crystal at the breakdown will not form carbides. After the overload is eliminated, the cable performance will not change, and normal use can still be continued.
3) High working temperature Since the melting point of the insulating layer of magnesium oxide crystal is much higher than the melting point of copper, the maximum normal working temperature of the cable can reach 250°C, and it can continue to operate at a temperature close to the melting point of copper of 1083°C in the short term.
4) Good anti-corrosion and explosion-proof performance. As the seamless copper tube is used as the sheath, the BTTZ cable has the performance of waterproof, moisture, oil and some chemical substances. The copper tube has considerable mechanical strength, so it has better explosion-proof performance.


5) Long service life BTTZ cables are all made of inorganic materials, so there is no insulation aging, and the service life can reach more than 3 times that of ordinary cables.
6) Greater flexibility in laying BTTZ cables can be laid on the bridge with ordinary cables, and can also be laid with special brackets, which is more flexible than ordinary cable laying. It also saves the investment in cable bridges and reduces the overall cost of the project.