What Is Cable Load?

Electric cable (power cable): usually consists of several wires or groups of wires.

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Cable (electric cable; power cable): usually by several wires or groups

Definition 1: Insulated by one or more

General principles

Cable

Cable Q & A

1. What types of commonly used wires and cables are classified according to purpose? Answer: It can be divided into bare wires, insulated wires, heat-resistant wires, shielded wires, power cables, control cables, communication cables, radio frequency cables, etc.

2. What are the types of insulated wires? Answer: There are the following types of insulated wires: PVC insulated wires, PVC insulated flexible wires, nitrile butadiene polyvinyl chloride mixed insulated wires, rubber insulated wires, agricultural underground buried aluminum core plastic insulated wires, rubber insulated cotton Textile cords, PVC insulated nylon sheathed wires, PVC insulated cords for power and lighting, etc.

3. Where is the cable bridge suitable? Answer: The cable bridge is suitable for laying power cables and control cables indoor and outdoor in general industrial and mining enterprises.

4. What are the cable accessories? Answer: Common electrical accessories include cable terminal junction boxes, cable intermediate junction boxes, connecting pipes and terminals, steel plate junctions, cable trays, etc.

5. What is the cable intermediate connector? Answer: The device that connects the cable with the cable's conductor, insulation shield, and protective layer to connect the cable line is called the cable intermediate connector.

Cable breakdown test

The breakdown test of the cable is to increase the voltage step by step until the insulation is broken down to obtain the breakdown voltage of the cable. The purpose of this type of test is to assess the safety margin between the ability of the cable insulation to withstand voltage and the working voltage. The strength of the AC breakdown electric field is one of the important parameters of cable design.

The AC breakdown strength has a great relationship with the boosting speed. Continuous boosting makes the cable breakdown in a few minutes called instantaneous breakdown. There is basically no thermal factor and it is a type of electrical breakdown. Therefore, such tests are generally not performed on wires and cables. The other is step-by-step boosting, starting from a lower voltage (for example, 0.5 to 2 times the operating voltage) and maintaining sufficient working time to allow the cable to fully generate electricity and heat in this voltage level. Then it rises to another voltage level. Step up until breakdown. The voltage of each stage rises step by step according to the percentage of initial pressurization. The factor of thermal breakdown is reflected in this test. Such test results have better reference value. It is often used when studying product characteristics.

Cable current formula

The current carrying capacity of a wire is related to the cross section of the wire, and also to the material, model, laying method, and ambient temperature of the wire. There are many influencing factors and the calculation is complicated.

The ampacity of various conductors can usually be found in the manual. However, with the help of some simple mental calculations, you can calculate directly without having to look up the table .

1. The relationship between the ampacity of the aluminum core insulated wire and the cross section

10 down five, 100 up two,

25, 35, four, three realms, 70, 95, twice and a half.

Pipe, temperature, 20% or 10% off.

Bare wire plus half.

Copper wire upgrade count.

Note: The formula for the ampacity of various sections is not directly pointed out, but is expressed by multiplying the section by a certain multiple.

To this end, the nominal cross-sections (square millimeters) of common wires in China are arranged as follows:

1, 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185 ...

(1) The first sentence states that the ampacity of the aluminum core insulated wire (A) can be calculated as a multiple of the section.

The Arabic numerals in the formula indicate the cross-section of the wire (square millimeters), and the Chinese characters represent the multiples. The relationship between the cross section and the multiple of the formula is as follows:

1 10	16, 25	35, 50	70, 95	120 or more
Five times	Four times	three times	Two and a half	Double

Contrast with the formula:

The formula "five under five" means that the cross section is below 10, and the current carrying capacity is five times the cross section value.

"100 on two" (read hundreds on two) means that the ampacity of a section of 100 or more is twice the value of the section.

The sections 25 and 35 are the boundaries between four and three times. This is the formula "25, 35, the Four Realms."

The cross sections 70 and 95 are 2.5 times. From the above arrangement, it can be seen that, with the exception of less than 10 and more than 100, the cross section of the middle conductor is the same multiple for every two specifications.

For example, the calculation of ampacity of aluminum core insulated wire when the ambient temperature is not greater than 25 :

When the cross-section is 6 square millimeters, the calculated ampacity is 30 amps.

When the cross section is 150 square millimeters, the calculated ampacity is 300 amps.

When the cross section is 70 mm2, the calculated ampacity is 175 amps.

It can also be seen from the above arrangement that the multiple decreases with the increase of the cross section, and the error is slightly larger at the boundary of the multiple conversion.

For example, the sections 25 and 35 are at the boundary between four and three times. 25 is a four-fold range. It is 100 amps according to the formula, but 97 amps according to the manual.

The 35 is the opposite, calculated as 105 amps, but the table is 117 amps. However, this has little effect on usage.

Of course, if you can "have something in your chest", when you choose the cross section of the wire, 25 will not let it reach 100 amps, and 35 will be more accurate than 105 amps.

Similarly, the 2.5mm square wire position is at the beginning of five times, but it is actually more than five times (the maximum can reach more than 20A).

However, in order to reduce the power loss in the wire, the current is usually not required to be so large, and the manual generally only indicates 12 amps.

(2) The next three sentences are the handling of changing conditions.

"Pipe-through, temperature, 20% off" means: if the pipe is laid (including the laying of trough plates, that is, the wire is covered with a protective cover layer, which is not exposed), the calculation will be 20%

If the ambient temperature exceeds 25 ° C, a 10% discount will be applied after calculation. If the pipe is laid and the temperature exceeds 25 ° C, then a 20% discount will be applied, or a simple 30% discount will be calculated.

Regarding the ambient temperature, it refers to the average maximum temperature of the hottest month in summer according to regulations. In fact, the temperature is fluctuating. In general, it does not affect the current carrying capacity of the wire.

Therefore, discounts are only considered when the temperature in some warm workshops or hotter areas exceeds 25 ° C.

For example, the calculation of the download flow of the aluminum core insulated wire under different conditions:

When the cross section is 10 square millimeters,

Then the ampacity is 10 × 5 × 0.8 = 40A

If the temperature is high, the ampacity is 10 × 5 × 0.9 = 45A

If it is through the pipe and high temperature, the current carrying capacity is 10 × 5 × 0.7 = 35 amps.

(3) For the ampacity of bare aluminum wire, the formula states that "bare wire plus half" means half after calculation.

This means that the current carrying capacity of bare aluminum wires with the same cross section can be increased by half compared with aluminum core insulated wires.

For example, calculation of ampacity of bare aluminum wire:

When the cross-section is 16 square millimeters, the current carrying capacity is 16 × 4 × 1.596A,

At high temperatures, the current carrying capacity is 16 × 4 × 1.5 × 0.9 = 86.4 amps.

(4) Regarding the current carrying capacity of copper conductors, the tactics point out that the upgrade calculation of copper conductors means that the cross-section arrangement order of copper conductors is increased by one level, and then calculated according to the corresponding aluminum conductor conditions.

For example, the environmental temperature of a bare copper wire with a cross section of 35 square millimeters is 25 ° C, and the current carrying capacity is calculated as: 50 × 3 × 1.5 = 225 amps if you upgrade to a 50 square millimeter bare aluminum wire.

For cables, there is no introduction in the recipe. Generally, the high voltage cables directly buried in the ground can be directly calculated by using the multiples in the first sentence.

For example, the buried current carrying capacity of a 35mm2 high-voltage armored aluminum core cable is 35 × 3 = 105 amps. 95 square millimeters is about 95 × 2.5238 amps.

In the three-phase four-wire system, the cross section of the neutral line is usually selected as about 1/2 of the cross section of the phase line. Of course, it must not be less than the minimum cross section allowed by mechanical strength requirements.

In a single-phase line, since the load currents passed by the neutral line and the phase line are the same, the cross section of the neutral line should be the same as that of the phase line.

Cable cost estimation

Material dosage

Calculation method of copper weight without conversion: cross-sectional area * 8.89 = kg / km, such as 120 square millimeters calculation: 120 * 8.89 = 1066.8kg / km

1. Amount of conductor: (Kg / Km) = d ^ 2 * 0.7854 * G * N * K1 * K2 * C /

d = copper wire diameter G = copper specific gravity N = number of pieces K1 = copper wire twist rate K2 = core wire twist rate C = number of insulated core wires

2. Insulation dosage: (Kg / Km) = (D ^ 2-d ^ 2) * 0.7854 * G * C * K2 D = insulation outer diameter d = conductor outer diameter G = insulation specific gravity K2 = core stranding rate C = Number of insulated core wires

3. Outer quilt dosage: (Kg / Km) = (D1 ^ 2-D ^ 2) * 0.7854 * G D1 = finished outer diameter D = upper outer diameter G = insulation specific gravity

4, the amount of tape: (Kg / Km) = D ^ 2 * 0.7854 * t * G * ZD = outer diameter of the process t = tape thickness G = tape specific gravity Z = overlap rate (1 / 4Lap = 1.25)

5. Winding dosage: (Kg / Km) = d ^ 2 * 0.7854 * G * N * Z d = copper wire diameter N = number of pieces G = specific gravity Z = twisting rate

6. Knitting amount: (Kg / Km) = d ^ 2 * 0.7854 * T * N * G / cos = atan (2 * 3.1416 * (D + d * 2)) * mesh number / 25.4 / T d = Braided copper wire diameter T = number of ingots N = number of each ingot G = copper specific gravity

Specific gravity: copper-8.89; silver-10.50; aluminum-2.70; zinc-7.05; nickel-8.90; tin-7.30; steel-7.80; lead-11.40; aluminum foil Myla-1.80; paper-1.35; myla-1.37 PVC- 1.45; LDPE-0.92; HDPE-0.96; PEF (foam) -0.65; FRPE-1.7; Teflon (FEP) 2.2; Nylon-0.97; PP-0.97; PU-1.21

Cotton tape-0.55; PP rope-0.55; Cotton yarn-0.48

Materials other than conductors

1. Sheath thickness: extruded outer diameter × 0.035 + 1 (in accordance with the power cable, the nominal thickness of the single-core cable sheath should be not less than 1.4mm, and the nominal thickness of the multi-core cable should not be less than 1.8mm)

2. On-line measurement of sheath thickness: Sheath thickness = (perimeter after extrusion sheath-perimeter before extrusion sheath) / 2 or sheath thickness = (perimeter after extrusion sheath-before extrusion sheath Perimeter) × 0.1592

3. The thinnest point of insulation thickness: nominal value × 90% -0.1

4. Thinnest point of unshielded shielding sheath: nominal value × 85% -0.1

5. Thinnest point of armor or shielding sheath: nominal value × 80% -0.2

6. Steel wire armouring: number = { × (inner sheath outer diameter + wire diameter)} wire diameter × ) weight ÷ (amount = × wire diameter & sup2; × × L × number ×

7. Weight of insulation and sheath = × (outer diameter before extrusion + thickness) × thickness × L ×

8. The weight of the steel strip = { × (outer diameter before wrapping + 2 × thickness -1) × 2 × thickness × × L} / (1 + K)

9, the weight of the tape = { × (outer diameter before wrapping + number of layers × thickness) × number of layers × thickness × × L / (1 ± K) where: K is the overlap rate or clearance rate, such as Overlap, it is 1-K; if it is a gap, it is 1 + K; is the specific gravity of the material; L is the cable length; twisting coefficient

Cable division

Difference from wires

In fact, "wire" and "cable" do not have strict boundaries. Generally, products with few cores, small product diameters, and simple structures are called wires, those without insulation are called bare wires, and others are called cables; those with a larger conductor cross-sectional area (greater than 6 mm2) are called large wires. Small ones (less than or equal to 6 square millimeters) are called small wires, and insulated wires are also called cloth wires.

Difference from optical cable

Cable: When the phone converts the acoustic signal into an electric signal and then transmits it to the switch via the line, the switch then sends the electric signal directly to the other phone to answer. The line transmitted during this call is the cable. Inside the cable are mainly copper core wires. The diameter of the core wire is divided into 0.32mm, 0.4mm and 0.5mm, the larger the diameter, the stronger the communication ability; there are also divided by the number of core wires: 5 pairs, 10 pairs, 20 pairs, 50 pairs, 100 pairs, 200 Wait, the logarithm mentioned here refers to the maximum number of users that the cable can accommodate; there is also a breakdown by package, which I don't know much about. Cable: Its volume, weight and communication ability are poor, and it can only be used for short-distance communication. Optical cable: When the phone converts the acoustic signal into an electrical signal and transmits it to the switch via the line, the switch then transmits this electrical signal to the photoelectric conversion device (converts the electrical signal into an optical signal) and transmits it to another photoelectric conversion device ( Convert the optical signal into an electrical signal), then go to the switching equipment and go to another phone to answer. The line between the two photoelectric conversion devices is an optical cable. It is said that it only has the number of core wires. The number of core wires is: 4, 6, 8, 12 pairs, and so on. Optical cable: its volume, small weight, low cost, large communication capacity, strong communication capabilities, etc. Due to many factors, it is only used for long-distance and point-to-point (ie, two exchange rooms) communication transmission. The difference between them is that the inside of the cable is copper core wire; the inside of optical cable is glass fiber. Optical cable Communication optical cable is a kind of communication line that uses a certain number of optical fibers to form a cable core according to a certain method. Field tests have been carried out in Shanghai, Beijing, Wuhan and other places. Soon after, it was tried out in the city's telephone network as an inter-office trunk line. After 1984, it was gradually used for long-distance lines and began to use single-mode fiber. Communication optical cable has larger transmission capacity than copper cable, long trunk distance, small size, light weight, and no electromagnetic interference. Since 1976, it has developed into trunk roads, city trunks, offshore and transoceanic subsea communications. , And the backbone of wired transmission lines such as local area networks and private networks, and began to develop into the field of user loop distribution networks in the city, providing transmission lines for fiber-to-the-home and wide-generation integrated service digital networks. The cable is usually a rope-like cable twisted by several or groups of wires [at least two in each group]. Each group of wires is insulated from each other and is often twisted around a center. The whole outer bread has a height Insulating cover; especially for submarine cables. First: there is a difference in material. The cable is made of metal (mostly copper, aluminum) as the conductor; the optical cable is made of glass fiber as the conductor. Second: there is a difference in the transmitted signal. The cable transmits electrical signals. Optical cables transmit optical signals. Third: there are differences in the scope of application. Cables are now mostly used for energy transmission and low-end data information transmission (such as telephones). Optical cables are mostly used for data transmission.

Difference from fiber

Cables are generally considered to be cables made of one or more insulated conductors that are insulated and protected from each other, and are used to transmit electricity or information from one place to another. In a broad sense, it refers to a device that transmits electrical signals using metal as a medium.

By definition, cables are used to conduct electricity. Generally made of the following metals:

Copper is second only to silver in conductivity and second to gold and silver in conductivity; it is corrosion resistant, non-magnetic, good in plasticity, easy to weld, and versatile. Copper alloy is mainly used to improve the wear resistance, corrosion resistance and mechanical and physical properties of copper.

Silver, metal has the highest electrical and thermal conductivity, has good corrosion resistance and oxidation resistance, and is easy to weld; mainly used for plating and cladding;

Gold and nickel are used as high temperature resistant wires.

Iron (steel), often used as a reinforcing material for composite conductors, such as steel core aluminum wire, copper-clad steel, aluminum-clad steel wire, etc.

Zinc, used as a coating for wire / steel strip / iron conductors to prevent corrosion.

Tin, used as a coating for steel wire / copper wire, is used to prevent corrosion and facilitate the welding of copper wires.

optical fiber

Optical fiber is an abbreviation of optical fiber, and it is a light transmission tool that uses the principle of total reflection of light in fibers made of glass or plastic. Former presidents of the Chinese University of Hong Kong, Gao Kun and George A. Hockham first proposed that optical fiber could be used for communication transmission. Gao Yan won the 2009 Nobel Prize in Physics.

The emitting device at one end of the optical fiber uses a light emitting diode (LED) or a laser beam to transmit light pulses to the optical fiber, and the receiving device at the other end of the optical fiber uses a photosensitive element to detect the pulse.

In daily life, since the conduction loss of light in optical fiber is much lower than the loss of electricity in electric wire, optical fiber is used for long distance information transmission.