Calculation of wire resistance. How to calculate the copper wire section and determine the load on the cable how to measure the thickness of the thin wire

In order to successfully buy a wire, before purchase it is necessary measure the diameter of the wireOtherwise you can become a victim of deception. Also measure the cross section of the wire will have to add a new electrical point on the old wiring, since the letter marking on it may not be. The information below will help you choose the procedure correctly. measurement of wire diameter And effectively use it in practice.

At the same time, you will immediately have a question: "What is the meaning of the company to spoil his reputation?" An explanation can be somewhat: but the thing is that even having the right calculations of the cross section of the wire, you can still face the problem, despite the fact that they buy wire with a suitable diameter. The accident can occur due to the fact that the cross section of the wires will be indicated on the labeling of the wires, which does not match the valid. This may happen as a result of the fact that the manufacturer's plant saved on the material, or by the company producing this product, all the characteristics of the product were not observed. Also, on the shelves, you can find wires on which there is no labeling, which initially makes it doubt their quality.

1. In order to save. For example, the plant made diameter wire It is only less than 2 mm. sq. with 2.5 mm dwelling, which gave the opportunity to win on one run meter Several kilograms of metal, not to mention the profit for mass production.

2. As a result of great competition, the company reduces the price of wiring, trying to lure most of consumers to itself. Naturally, this is due to reducing the wire diameterthat it is impossible to determine the naked eye.

And the first, and the second option takes place on the sales market, so you better rebuild and make yourself accurate calculations that will be discussed further.

Three main ways to determine the diameter of the wire.

There are several ways, but at the heart of each of them lies definition of diameters Cases with subsequent calculations of final results.

Method first. Using devices. Today there are a number of devices that help measure the diameter of the wire or veins wires. This is a micrometer and caliper, which are both mechanical and electronic (see below).

This option is primarily suitable for professional electricians who are constantly engaged in the installation of wiring. The most accurate results can be obtained using a caliper. This technique has the advantages in what is possible conduct measuring wire diameter Even on the part of the working line, for example, in the outlet.

After you measured diameter wire, It is necessary to conduct calculations according to the following formula:

It is necessary to remember that the number "PI" is 3.14, respectively, if we divide the number "PI" by 4, we can simplify the formula and to reduce the calculation to the multiplication of 0.785 to the diameter in the square.

Method of the second. We use a ruler. If you decide not to spend money on the device, which is logical in this situation, can you use a simple proven method for measuring the cross section of a wire or wire?. You will need a simple pencil, ruler and wire. Clean the core of isolation, cheapest it tightly on a pencil, and after that, the line is measured long length Winding (as shown in the figure).

Then the wound wire is divided by the number of lived. Obtained and will diameter of cross section of wire.

But at the same time consider the following:

• the more lived you wrap on a pencil, the more accurate there will be a result, the number of turns should be at least 15;
• twist turns tightly to each other so that there are no free space between them, it will significantly reduce the error;
• spend measurements several times (change the side of the measurement, direction of the line, etc.). Several results will help you again avoid a big error.

Pay attention to the minuses of this measurement method:

1. Only can only be measured by a section of thin wires, since the thick wire can hardly be winding on a pencil.

2. To begin with, you will need to purchase a small piece of items before making a basic purchase.

The formula that was talked above is suitable for all measurements.

The third way. We use the table. In order not to calculate the formula, you can use a special table in which specified wire diameter? (in millimeters) and conductor cross section (in millimeters square). The finished tables will give you more accurate results and will significantly save your time that you do not have to spend on calculations.

Wiring B. modern apartments Provides maximum operating current in the network up to 25 amps. Under such a parameter calculated and protective automatainstalled in distribution shield Apartments. The cross-section of the wire at the entrance to the room should be at least 4 mm2. When the internal layout device is permissible to use cables with a cross section of 2.5 mm2, which are calculated for a current of 16 amps.

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Measurement of wire diameter

According to the standard, the wire diameter must comply with the declared parameters that are described in the marking. But the actual size may differ from the declared by 10-15 percent. This is especially true of cables that are made by small firms, but major manufacturers can be problems. Before buying an electrical wire for transmitting high current, it is recommended to simulate the conductor diameter. For this can be applied various methods, distinguished by error. Before performing the measurement, it is necessary to clean the cable veins from isolation.

Measurements can be made directly in the store, if the seller is allowed to remove isolation with small plot Wires. Otherwise, you will have to get a small segment of the cable and make measurement on it.

Micrometer

The maximum accuracy can be obtained by micrometers that have a mechanical and electronic circuit. On the tool terminal, there is a scale with a division price of 0.5 mm, and there are 50 wrapping on the drum circle with a fission price of 0.01 mm. Characteristics are the same in all models of micrometers.

When working with a mechanical device, the sequence of actions should be followed:

1. The rotation of the drum is set to the gap between the screw and the heel close to the measured size.
2. Take the screw with a ratchet tight to the surface of the measured part. The eyeliner is performed by rotating hand without effort until the ratchet is triggered.
3. Calculate the transverse diameter of the details according to the testimony on the scales placed on the stem and the drum. The diameter of the product is equal to the sum of the value on the rod and the drum.

Measuring mechanical micrometer

Working with an electron micrometer does not require rotation of the nodes, it displays the value of the diameter on the liquid crystal screen. Before using the instrument, it is recommended to check the settings, since electronic devices are measured in millimeters and inches.

Schunzirkul

The device has a reduced accuracy compared to the micrometer, which is enough to measure the conductor. The calipers are equipped with a flat scale (nonius), a circular dial or digital display on a liquid crystal display.

To measure the transverse diameter, it is necessary:

1. Click the measured conductor between sponges of the caliper.
2. Calculate the value on the scale or watch it on the display.

An example of calculating size on nonius

Ruler

The measurement of the ruler gives a rough result. To perform measurement, the use of tool lines that have greater accuracy is recommended. The use of wooden and plastic school products will give a very approximate diameter value.

For measurement, the ruler is necessary:

1. Clean the insulation piece of the wire with a length of up to 100 mm.
2. Tightly wind the resulting segment on a cylindrical subject. The turns must be complete, that is, the beginning and end of the wire in the winding are directed in one direction.
3. Measure the length of the resulting winding and divided by the number of turns.

Measurement of diameter by a ruler by the number of turns

In the example above, there are 11 turns of the wires that are in a length of about 7.5 mm. Dividing the length by the amount of turns, you can determine the approximate diameter value, which in this case is 0.68 mm.

On the sites of stores selling electric wiresThere are online calculators that allow you to calculate the cross section on the number of turns and the length of the obtained helix.

Determining section of diameter

After determining the diameter of the wire, you can proceed to calculate the cross-sectional area in squares (mm2). For VG type cables consisting of three single-core conductors, the calculation methods are used according to the formula or on the finished table of the correspondence of diameters and areas. Methods are applicable for products with different labeling.

According to the formula

The main method is the calculation of the formula of the form - S \u003d (n / 4) * d2, where π \u003d 3.14, and D is the measured diameter. For example, to calculate the area with a diameter of 1 mm, it will be necessary to calculate the value: S \u003d (3.14 / 4) * 1² \u003d 0.785 mm2.

Online calculators are available on the network, which allow you to calculate the area of \u200b\u200bcircle in diameter. Before buying a cable, it is recommended to calculate the values \u200b\u200bin advance, bring to the table and use it in the store.

In the videotage from the user, Alexander Kvasha demonstrates the check section of the live wire.

On a table with frequent diameters

To simplify the calculation, it is convenient to use the finished table.

The procedure for using numbers from the table:

1. Select the type of wire, which is supposed to purchase, for example, VG 3 * 4.
2. Determine the diameter on the table - section 4 mm2 corresponds to the diameter of 2.26 mm.
3. Check the actual value of the wire diameter. In the case of coincidence, products can be purchased.

Below is a table of the relationship of the centers of the main types of copper wiring to the diameters and current (at a voltage of 220 V).

An additional criterion for matching the diameter is the weight of the wire. The method of determining the weight diameter is used when checking thin wire for winding transformers. Product thickness begins from 0.1 mm, and it is problematic to measure using a micrometer.

A brief table of matching alkali diameters by weight is shown below. The detailed data is available in stores specializing in the sale of electronic components.

When calculating the diameter of the wire for fuses, the conductor material should be taken into account. A brief table of matching cable diameters from common types of material and current strength is shown below.

For a stranded cable

The diameter of the stranded cable is determined by the size of the cross section of one conductor multiplied by their number. The main problem is to measure the diameter of the thin wire.

An example is a cable consisting of 25 lived with a diameter of 0.2 mm. According to the above formula, the cross section is: S \u003d (3.14 / 4) * 0.2² \u003d 0.0314 mm2. With 25 veins, it will be: S \u003d 0.0314 * 25 \u003d 0.8 mm2. Then, according to the tables, it is determined - it is suitable for transmitting the current required strength or not.

Another method of approximate calculation of the current force is the method of multiplying the diameter of the stranded cable to the adjustment indicator 0.91. The coefficient provides for a nonmonolite wire structure and aerial gaps Between the turns. The measurement of the outer diameter is carried out with a little effort, since the surface is easily deformed and the cross section becomes oval.

When calculating the segment part of the cable, formulas are used or table values. The table shows the standard magnitude of the width and height of the segment.

Photo Gallery

Segment cable (extreme right) Cable segment

Table of power consumption of electrical appliances

Common way to determine required section The wire is the method of calculating the peak power. In order to find out the load, you can use the standard table in which the power and peak values \u200b\u200bof the current consumption are reduced for household appliances.

The current will consume a refrigerator, electrical appliances in the duty state (TVs, radiotelephones), chargers. The total value of power consumption by devices is considered within 0.1 kW.

When connecting all available household appliances, the current can reach 100-120 A. This option is unlikely, so when calculating the load, the common connection combinations take into account.

For example, in the morning it can be used:

• electric kettle - 9.0 A;
• microwave oven - 10.0 A;
• toaster - 7 A;
• coffee grinder or coffee maker - 8 A;
• other appliances and lighting - 3 A.

The final consumption of instruments can reach: 9 + 10 + 7 + 8 + 3 \u003d 37 A. There are also calculators that allow you to calculate the current for power consumption and voltage.

Select the cable using the maximum current tables in the network

Two types of data from the table above are applied to calculate:

• in total power;
• by the magnitude of current consumption.

There are tables of standard values \u200b\u200bthat allow you to determine the necessary diameter and section that are then checked on the wired wire. The resulting indicator is rounded up to the coincidence with real existing diameter cable.

In residential premises, it is impossible to use wires with an excessive cross section, as they have a large resistance, which leads to a voltage drop.

For copper cable

To calculate the copper conductor, a table is applied for a voltage of 230 V.

For aluminum cable

To calculate the wire from aluminum, the table below can be used (data is taken for voltage 230 V).

Cable selection on PUE and GOST tables

When buying a wire, it is recommended to see the standard GOST standard or the conditions of which the product is made. GOST requirements are higher than similar parameters. technical Conditions, Therefore, it is necessary to prefer products made according to the standard.

Tables from the rules of the device of electrical installations (PUU) are the dependence of the force transmitted over the conductor from the cross section of the vein and the laying method in the trunk tube. The permissible strength of the current decreases as the individual cores or the use of a stranded cable in isolation increases. The phenomenon is associated with a separate item in PUE, which stipulates the parameters of the maximum allowable heating of the wires. Under the trunk tube is a box, including plastic or when laying the wiring with a beam on the cable tray.

In theory, the conductor diameter must comply with the declared parameters. For example, if it is indicated on the marking that the cable is 3 x 2.5, then the conductor cross section should be 2,5 mm 2. In fact, it turns out that the different size can differ by 20-30%, and sometimes more. What threatens it? Overheating or placing isolation with all the ensuing consequences. Therefore, before buying, it is desirable to find out the size of the wire to determine its cross section. How exactly consider the cross section of the wire in diameter and will find out further.

How and how to measure the diameter of the wire (wire)

To measure the diameter of the wire, the caliper or micrometer of any type (mechanical or electronic) is suitable. It is easier to work with electronic, but they are not all. It is necessary to measure the living well without isolation, therefore it is pre-moved it or remove the small piece. This can be done if the seller is allowed. If not, buy a small piece for testing and spend the measurements on it. On the insulation, the conductor measure the diameter, after which it is possible to determine the actual cross-section of the wire on the sizes.

What measuring device In this case, better? If we talk about mechanical models, then micrometer. It has accuracy of measurements above. If we talk about electronic options, then for our purposes they both give quite reliable results.

If there is neither a caliper, nor micrometer, capture a screwdriver and a ruler. We have to clean a pretty decent piece of the conductor, so without buying a test pattern this time is hardly hampered. So, remove isolation from a piece of wires 5-10 cm. Wash the wire on the cylindrical part of the screwdriver. The coils are placed close one to another, without clearance. All turns must be complete, that is, the "tails" of the wires must be stitching in one direction - up or down, for example.

The number of turns is not important - about 10. It is possible more or less, just to divide it easier. Throwing turns, then apply the resulting winding to the ruler, aligning the beginning of the first turn with a zero mark (as in the photo). Measure the length of the area occupied by the wire, then it divides it to the number of turns. Get the wire diameter. That's it simple.

For example, we consider what the size of the wire shown in the photo above. The number of turns in this case is 11, they occupy 7.5 mm. We divide 7.5 to 11, we get 0.68 mm. This will be the diameter of this wire. Next, you can search for the section of this conductor.

We are looking for a wire section in diameter: formula

Wires in the cable have a circle in cross section. Therefore, in the calculations, we use the formula of the area of \u200b\u200bthe circle. It can be found using radius (half of the measured diameter) or diameter (see formula).

Determine the cross section of the wire in diameter: formula

For example, consider the area cross section Explorer (wire) in size calculated earlier: 0.68 mm. Let's first use the formula with a radius. First we find a radius: we divide the diameter for two. 0.68 mm / 2 \u003d 0.34 mm. Next this figure we substitute in the formula

S \u003d π * R 2 \u003d 3,14 * 0.34 2 \u003d 0.36 mm 2

It is necessary to count this way: first we will be erected into a square 0.34, then multiply the value obtained by 3.14. Received a cross section of this wire 0.36 square millimeters. This is a very thin wire, which is not used in power networks.

Let's calculate the cable cross section in diameter using the second part of the formula. It should be exactly the same meaning. The difference can be in thousands of shares due to different rounding.

S \u003d π / 4 * d 2 \u003d 3.14 / 4 * 0,68 2 \u003d 0.785 * 0,4624 \u003d 0.36 mm 2

In this case, we divide the number 3.14 to four, then we will be erected into a square, the two figures obtained with a variant. We get a similar value, as it should be. Now you know how to find out the cable cross section in diameter. Which of these formulas are more convenient for you, that and use. No difference.

Table matching the diameters of the wires and their cross-section area

Conduct settlements in the store or in the market does not always want or have the opportunity. In order not to spend time on calculations or not mistaken, you can use the table of conformity of diameters and sections of the wires in which there are the most common (regulatory) dimensions. It can be rewritten, print and capture with you.

How to work with this table? As a rule, on cables there is a marking or tag on which its parameters are indicated. There is a cable marking, the amount of lived and their cross section. For example, 2x4. We are interested in the parameters of the veins. And these are numbers that stand after the sign "x". In this case, it is stated that there are two conductor having a cross section of 4 mm 2. So we will check whether this information is true.

How to work with a table

To check, measure the diameter of any of the described methods, then refer to the table. It indicates that with such a section in four square millimetersThe wire size must be 2.26 mm. If you have the same or very close measurements (measurement error exists, as non-ideal instruments), everything is fine, you can buy this cable.

But much more often the actual diameter of the conductors is significantly less than the stated. Then you have two ways: search for a wire of another manufacturer or take a larger cross section. For him, of course, you will have to overpay, but the first option will require a rather large period of time, and not the fact that you will be able to find the corresponding GOST cable.

The second option will require more moneySince the price is significantly dependent on the declared section. Although, not a fact - good cableMade in all standards may be even more expensive. This is understandable - copper costs, and, often, and isolation, while compliance with technology and standards, is much larger. Therefore, manufacturers and chitryat, reducing the diameter of the wires - to reduce the price. But such savings can turn into trouble. So be sure to measure before purchasing. Even proven suppliers.

And also: inspect and swell insulation. It should be thick, solid, have the same thickness. If, in addition to changing the diameter, the problem is also with isolation - look for a cable of another manufacturer. In general, it is advisable to find products that meets the requirements of the GOST, and not done on that. In this case, there is hope that the cable or the wire will serve for a long time and without problems. Today it is not easy to do, but if you breed or, the quality is very important. Therefore, it is probably to search.

How to determine the cross section of the stranded wire

Sometimes conductors are used stranded - consisting of many identical thin wires. How to calculate the cross section of the wire in diameter in this case? Yes, just too. Perform measurements / calculations for one wire, consider their number in the beam, then multiply on this number. Here you will learn the cross-sectional area of \u200b\u200bthe stranded wire.