How to choose a wire according to the current national standard

National standards have not been seen, and even if there is, they are reference standards from decades ago, and only the electrician's manual has reference standards; Let's take a look at the article "Economic Choice of Wire Cross-Sections" written by me. can make a difference.

Simple formula: a kilowatt motor has a current size of about two amperes. So the current can be approximated to take the kilowatt of the motor multiplied by 2The wire selected by the motor should be multiplied by the square number of the cable according to the current carrying capacity of the cable, which is greater than or equal to the rated working current of the hidden motor.

First of all, it is necessary to know the voltage used by the appliance and the rated power of the appliance.

Secondly, according to the voltage and power, calculate the working current of the appliance when it is in normal use.

Finally, according to the current carrying value table of the wire, select the wire corresponding to the wire diameter.

For example, a heater is rated at 220V.

Then the normal working current of this heater = power voltage = 2200 220 = 10a.

At this time, the square or more copper core wire should be selected.

Simple formula: the current size of a kilowatt motor is two amperes, and the number of stoves on the left is on the right. The buried current can be approximated by multiplying the number of kilowatts of the motor by 2

The wire selected by the motor should be multiplied by the square number of the cable according to the current carrying capacity of the cable, which is greater than or equal to the rated working current of the motor.

First of all, it is necessary to know the voltage used by the appliance and the rated power of the appliance.

Secondly, according to the voltage and power, calculate the working current of the appliance when it is in normal use.

Finally, according to the current carrying value table of the wire, select the wire corresponding to the wire diameter.

For example, a heater is rated at 220V.

Then the normal working current of this heater = power voltage = 2200 220 = 10a.

At this time, the square or more copper core wire should be selected.

"Code for Design of Power Supply and Distribution System" GB50052-2009 "2008 Code for Electrical Design of Civil Buildings" and many other national standards are based on the qualified rate of voltage, the qualified rate of line loss, and the current carrying capacity to select wires.

There are four principles that must be met when selecting a wire:

1) Select the cross-section of the wire (safe ampacity) according to the heating conditions for the short distance and small load, and control the current with the heating conditions of the wire, the smaller the cross-sectional area, the better the heat dissipation, and the greater the current passing through the unit area.

2) Long-distance and medium-load on the basis of safe ampacities, according to the voltage loss conditions to select the wire cross-section, long-distance and medium-load is not enough to not heat, but also to consider the voltage loss, to ensure that the voltage to the load point in the qualified range, electrical equipment can work normally.

3) Large pitch and small load should also be based on the force of the wire, consider the mechanical strength, and ensure that the wire can withstand the tensile force.

4) On the basis of qualified safe current carrying capacity and voltage drop, the large load is selected according to the economic current density, that is, the power loss should also be considered, and the power loss and capital investment should be in the most reasonable range.

Safe ampacities of the wire.

In order to ensure the continuous operation of the wire for a long time, the allowable current density is called the safe ampacity.

The general regulations are: copper wire selection 5 8a mm2; Aluminum wire selection 3 5a mm2.

The safe current carrying capacity should also be determined according to the ultimate temperature, cooling conditions, laying conditions and other comprehensive factors of the core use environment of the wire.

Under normal circumstances, the distance is short, the cross-sectional area is small, the heat dissipation is good, the temperature is low, etc., the conductivity of the wire is stronger, and the upper limit of the safe current carrying capacity is selected;

Long distance, large cross-sectional area, poor heat dissipation, high temperature, poor natural environment, etc., the conductivity of the wire is weaker, and the lower limit of safe current carrying is selected;

For example, the conductivity of bare wires is stronger than insulated wires, overhead wires are stronger than cables, cables buried in the ground are stronger than cables laid on the ground, and so on.

For example, the 15kw three-phase motor selector cable.

The rated current of the three-phase motor is i=p

If it is a close distance (within a few tens of meters), the copper cable is 6 square millimeters, and the aluminum cable is 10 square millimeters.

If it is a long distance (more than 100 meters), the copper cable is 16 square millimeters, and the aluminum cable is 25 square millimeters.

If it is between long distance and short distance, the copper cable is 10 square millimeters and the aluminum cable is 16 square millimeters.

This is electricity knowledge, there is no standard for how you choose. It is the designer who selects the line according to the actual situation, the distance of the line.

05 series building standard design atlas 05D4 outdoor cable engineering, as well as general electrician manuals or something.

CCC certification mark.

There must be CCC certification mark on the wire, wire and cable products are national compulsory safety certification products, all manufacturers must obtain the "CCC" certification certified by the China Electrical Products Certification Committee, obtain the "CCC" certification mark, and have the "CCC" certification mark on the certificate or product. The wire is related to the safety of electricity, and the bad wire will affect the safety of our life and property, so we must choose the wire product with the CCC certification mark.

Wire appearance. The appearance of a good wire product should be smooth and round, and the color is uniform, so we should disassemble and check the wire when purchasing to see if the appearance is uniform.

Product Certificate.

The wire product certificate will be the "CCC" certification logo, trademark, model specification, rated voltage, length, inspection, manufacturing date, implementation standard, factory name, factory address, ** and other logos are printed clearly, and in line with the product, these will be the production products of regular manufacturers, we should see clearly when purchasing.

Wire conductors. The conductor of the wire should be shiny, and the DC resistance and conductor structure size should meet the requirements of the national standard. The wire and cable products that meet the requirements of the national standard, whether it is an aluminum conductor or a copper conductor, are relatively bright and oil-free, so the DC resistance of the conductor is fully in line with the national standard, with good conductivity and high safety. How to purchase wires.

Wire specifications. Wire specifications are very important, and generally household power cords should use BVV2 and BVV2 type wires. BVV is the national standard code, which is the copper sheathed wire BVV2 and BVV2, which represent 2 cores square millimeters and 2 cores square millimeters respectively. In general, BVV2 is used as the main line and trunk line, and BVV2 is used as a single electrical branch line and switch line.

BVV2 4 for one-way air-conditioning line, with dedicated ground wire.

Power selects wires.

1. Single-phase 220V voltage, power appliances, rated current of I=P U=16 square copper wire and 25 square aluminum wire bearing current is 100A, and a smaller specification of wire can not reach 70A, 2, three-phase 380V voltage, power appliances, rated current of about 31A. The carrying current of 6 square copper wire and 10 square aluminum wire is about 40A.

The relationship between the cross-sectional area of the line and the current.

The general copper wire safety calculation method is:

The safe ampacity of the square millimeter copper power cord is 28A.

The safe ampacity of the 4 square mm copper power cord is 35A.

The safe ampacity of the 6 square mm copper power cord is 48A.

The safe ampacities of the 10 square mm copper power cord are 65A.

The safe ampacity of the 16 square mm copper power cord is 91A.

The safe current carrying capacity of the 25 square mm copper power cord is 120A.

According to the power current of 40kw about 72A, select YJV 16 square three-core wire See the red line in the figure.

Wire refers to the wire that transmits electric energy, divided into bare wire, magnet wire and insulated wire, people need to consider the model rules when choosing wire, and need to pay attention to the relationship between wire specifications and current. What exactly is the relationship between wire size and current? Today, I will answer them one by one for you.

First, the model and specification of the wire.

The specification is composed of rated voltage, number of cores and nominal cross-section.

The general rated voltage of wires and control cables is 300 300V, 300 500V, 450 750V;

The rated voltage of medium and low voltage power cables is generally equal.

The number of cores of wires and cables is determined according to actual needs, and the general power cable mainly has a simple core, and the wire is mainly 1 5 cores, and the control cable has 1 61 cores.

The nominal cross-section is an approximation of the cross-section of the guide. In order to achieve the specified DC resistance, an integer value near the cross-section of a conductor is specified for easy memorization and uniformity. The conductor cross-section of China's unified regulations is , noisy and so on.

It should be emphasized here that the nominal cross-section of the conductor is not the actual cross-section of the conductor, and the actual cross-section of the conductor is much smaller than the nominal cross-section, and several are larger than the nominal cross-section. In the actual production process, as long as the DC resistance of the conductor can meet the specified requirements, it can be said that the cross-section of the cable is up to standard.

Second, the relationship between wire specifications and current.

The thicker the wire, the greater the amount of current passing through, and the wire selection method is as follows:

1. Good drum packaging can reduce the wear of the insulation layer caused by production, transportation and handling, and facilitate the installation of electricians. There is a complete certificate in the package, and the certificate should include complete information such as specifications, implementation scale, rated voltage, length, date, factory name and address.

2. Be sure to see whether the length and thickness of the core have been moved. In the relevant scale, the error of the length of the wire can not exceed 2%, and the diameter of the cross-section line can not be exceeded, but there are a large number of short catties in the length of the market, and there is fraud on the cross-section (such as the line marked with a cross-section of square millimeters, but in fact it is only 2 square millimeters thick).

3. The insulation layer of fake and shoddy wires seems to be very thick, but in fact, most of them are made of recycled plastic, as long as you squeeze it a little harder, the extrusion will be white, and some powder will fall. wires, which are generally within the delineated weight range. For example, the commonly used plastic insulated single-strand copper core wire with a cross-sectional area is weighed every 100m.

It can be seen that the thickness of the wire is approximately proportional to the size of the current, and the diameter is proportional to the current, rather than the cross-sectional area.

The specifications are mainly 1 square, square, square, etc.; It is determined according to three factors: wire material and wire cross-sectional area, and wire laying conditions.

In electric power engineering, the current carrying capacity of the conductor is determined by three factors: the conductor material, the conductor cross-sectional area, and the conductor laying conditions. A single wire can take a higher current carrying capacity than multiple parallel wires; The open wire laying wire can take a higher current carrying capacity than the wire laid through the pipe; Copper conductors can have a higher ampacarrying capacity than aluminum conductors.

The wire load current value specified in the Chinese national standard GB T requires that the allowable long-term load current of 1 square copper core wire is 8A-12A; The square copper core wire allows the long-term load current to be 12A-15A; The square copper core wire allows the long-term load current to be 16A-25A; The allowable long-term load current of 4 square copper core wire is 25A-32A; The allowable long-term load current of 6 square copper core wire is 32A-40A.