How to measure the thickness of a copper wire. How to calculate the cross-section of a copper wire and determine the load on the cable

Wiring in modern apartments provides for a maximum operating current in the network up to 25 Amperes. The circuit breakers installed in the switchboard of the apartment are also designed for this parameter. The cross-section of the wire at the entrance to the room must be at least 4 mm2. When installing internal wiring, it is permissible to use cables with a cross section of 2.5 mm2, which are designed for a current of 16 Amperes.

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Measuring wire diameter

According to the standard, the diameter of the wire must correspond to the declared parameters, which are described in the marking. But the actual size may differ from the declared one by 10-15 percent. This is especially true for cables that are manufactured by small firms, but large manufacturers may also have problems. Before buying an electric wire for transmitting currents of great importance, it is recommended to measure the diameter of the conductor. For this can be applied different ways differing in error. Before taking a measurement, it is necessary to clean the cable cores from insulation.

Measurements can be made directly in the store, if the seller allows you to remove the insulation from small area wires. Otherwise, you will have to purchase a small piece of cable and make a measurement on it.

Micrometer

Maximum accuracy can be obtained with micrometers that have mechanical and electronic circuit... On the shank of the tool there is a scale with a graduation of 0.5 mm, and on the drum circle there are 50 lines with a graduation of 0.01 mm. The characteristics are the same for all micrometer models.

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

1. By rotating the drum, the gap between the screw and the heel is set close to the measured size.
2. Place the screw with the ratchet closer to the surface of the workpiece to be measured. The lead-in is performed by hand rotation without effort until the ratchet is triggered.
3. Calculate the transverse diameter of the part according to the indications on the scales located on the stem and drum. The diameter of the product is equal to the sum of the values ​​on the rod and on the drum.

Measurement with a mechanical micrometer

Working with an electronic micrometer does not require the rotation of the units; it displays the diameter value on the liquid crystal screen. It is recommended to check the settings before using the appliance, as electronic devices measured in millimeters and inches.

Caliper

The device has a reduced accuracy in comparison with a micrometer, which is quite enough for measuring a conductor. Calipers are equipped with a flat scale (vernier), circular dial or digital indication on the liquid crystal display.

To measure the transverse diameter, you must:

1. Clamp the guide to be measured between the jaws of the caliper.
2. Calculate the value on the scale or see it on the display.

An example of calculating the size on a vernier

Ruler

Measuring with a ruler gives a rough result. To take measurements, it is recommended to use instrument rulers, which have high accuracy. Using wooden and plastic school products will give a very rough estimate of the diameter.

To measure with a ruler, you must:

1. Remove the insulation from a piece of wire with a length of up to 100 mm.
2. Wrap the resulting piece tightly onto a cylindrical object. The turns must be full, that is, the beginning and end of the wire in the winding are directed in the same direction.
3. Measure the length of the resulting winding and divide by the number of turns.

Measuring the diameter with a ruler by the number of turns

In the example above, there are 11 turns of wire that are about 7.5 mm long. By dividing the length by the number of turns, you can determine the approximate value of the diameter, which in in this case equal to 0.68 mm.

On the websites of stores selling electric wires, there are online calculators that allow you to calculate the cross section by the number of turns and the length of the resulting spiral.

Determination of a section by diameter

After determining the diameter of the wire, you can start calculating the cross-sectional area in squares (mm2). For cables of the VVG type, consisting of three single-core conductors, calculation methods are used according to the formula or according to a ready-made table of correspondence of diameters and areas. The methods are applicable to products with other markings.

According to the formula

The main method is to calculate using a formula of the form - S = (n / 4) * D2, where π = 3.14, and D is the measured diameter. For example, to calculate the area with a diameter of 1 mm, you will need to calculate the value: S = (3.14 / 4) * 1² = 0.785 mm2.

Online calculators are available on the network that allow you to calculate the areas of a circle by diameter. Before buying a cable, it is recommended to calculate the values ​​in advance, put them in a table and use it in the store.

The video from the user Alexander Kvasha demonstrates how to check the cross-section of the wire cores.

According to the table with common diameters

To simplify the calculation, it is convenient to use a ready-made table.

The order of using numbers from the table:

1. Select the type of wire that is supposed to be purchased, for example, VVG 3 * 4.
2. Determine the diameter according to the table - a cross-section of 4 mm2 corresponds to a diameter of 2.26 mm.
3. Check the real value of the wire diameter. If there is a match, the products can be purchased.

Below is a table of the ratio of the cross-sections of the main types of copper wiring to the diameters and current (at a voltage of 220 V).

An additional criterion for the compliance of the cross-section with the diameter is the weight of the wire. The method of determining the diameter by weight is used when checking thin wire for winding transformers. The thickness of the product starts from 0.1 mm, and it is difficult to measure it with a micrometer.

Brief table matching vein diameters by weight is given below. Detailed data are available in stores specializing in the sale of electronic components.

When calculating the wire diameter for fuses, the material of the conductor must be taken into account. A brief table of the correspondence of cable diameters from common types of material and amperage is given below.

For stranded cable

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

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

Another way to roughly calculate the current is by multiplying the diameter of a multicore cable by a correction factor of 0.91. The coefficient provides for a non-monolithic wire structure and air gaps between the turns. The outer diameter is measured with little effort, since the surface is easily deformed and the section becomes oval.

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

Photo gallery

Segment cable (far right) Cable segment

Power consumption table of electrical appliances

A common way to determine the required wire size is the peak power calculation method. In order to find out the load, you can use the standard table, which summarizes the power parameters and the peak current consumption for household appliances.

The current will be consumed by the refrigerator, electrical appliances on duty (TVs, radio telephones), charging device... 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 connection option is unlikely, therefore, when calculating the load, common connection combinations are taken into account.

For example, in the morning the following can be used:

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

The total consumption of devices can reach: 9 + 10 + 7 + 8 + 3 = 37 A. There are also calculators that allow you to calculate the current based on power consumption and voltage.

Cable selection according to the tables of maximum current in the network

Two types of data from the above table are used for the calculation:

• by total power;
• by the amount of current consumed by the devices.

There are tables of standard values ​​that allow you to determine the required diameter and section, which are then checked on the purchased wire. The found indicator is rounded up to coincide with the actual cable diameter.

In residential premises, wires with an excessive cross section cannot be used, since they have a high resistance, which leads to a voltage drop.

For copper cable

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

For aluminum cable

The table below can be used to calculate the aluminum wire (data taken for 230 V).

The choice of cable according to the tables PUE and GOST

When buying a wire, it is recommended to look at the GOST standard or the TU conditions according to which the product is manufactured. GOST requirements are higher than similar parameters technical conditions, therefore, products made to the standard should be preferred.

Tables from the rules for electrical installations (PUE) represent the dependence of the strength of the current transmitted through the conductor on the cross-section of the core and the method of laying in the main pipe. The permissible current decreases as the individual cores increase or the use of multi-core cables in insulation. The phenomenon is associated with a separate paragraph in the PUE, which stipulates the parameters of the maximum permissible heating of wires. A trunk pipe means a box, including a plastic one or when laying the wiring in a bundle on a cable tray.

In theory, the diameter of the conductors should correspond to the declared parameters. For example, if it is indicated on the marking that the cable is 3 x 2.5, then the cross-section of the conductors should be exactly 2.5 mm 2. In fact, it turns out that the actual size can differ by 20-30%, and sometimes even more. What is the threat? Overheating or melting of insulation with all the ensuing consequences. Therefore, before buying, it is advisable to know the size of the wire in order to determine its cross section. How exactly to calculate the cross-section of the wire by diameter and we will find out further.

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

To measure the diameter of the wire, a vernier caliper or any type of micrometer (mechanical or electronic) is suitable. It's easier to work with electronic ones, but not everyone has them. It is necessary to measure the core itself without insulation, so first move it aside or remove a small piece. This can be done if the seller allows it. If not, buy a small piece for testing and measure on it. On a conductor stripped of insulation, measure the diameter, after which you can determine the real cross-section of the wire according to the dimensions found.

Which measuring device is it better in this case? If we talk about mechanical models, then a micrometer. Its measurement accuracy is higher. If we talk about electronic options, then for our purposes they both give quite reliable results.

If you don't have a caliper or micrometer, take a screwdriver and a ruler with you. We'll have to clean up a pretty decent piece of conductor, so you can hardly do without buying a test sample this time. So, remove the insulation from a piece of wire 5-10 cm. Wrap the wire on the cylindrical part of the screwdriver. Lay the coils close to one another, without a gap. All turns must be full, that is, the "tails" of the wire must stick out in one direction - up or down, for example.

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

For example, let's calculate 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 by 11, we get 0.68 mm. This will be the diameter of this wire. Next, you can search for the cross section of this conductor.

We are looking for a wire cross-section by diameter: formula

The wires in the cable are circular in cross-section. Therefore, in the calculations we use the formula for the area of ​​a circle. It can be found using radius (half of the measured diameter) or diameter (see formula).

Determine the cross-section of the wire by diameter: formula

For example, let's calculate the cross-sectional area of ​​the conductor (wire) according to the size calculated earlier: 0.68 mm. Let's use the radius formula first. First, we find the radius: we divide the diameter by two. 0.68 mm / 2 = 0.34 mm. Next, we substitute this figure into the formula

S = π * R 2 = 3.14 * 0.34 2 = 0.36 mm 2

It is necessary to count like this: first we square 0.34, then multiply the resulting value by 3.14. Received the cross-section of this wire 0.36 square millimeters. This is a very thin wire that is not used in power networks.

Let's calculate the diameter of the cable using the second part of the formula. You should get exactly the same value. The difference can be in thousandths due to different rounding.

S = π / 4 * D 2 = 3.14 / 4 * 0.68 2 = 0.785 * 0.4624 = 0.36 mm 2

In this case, we divide the number 3.14 by four, then we square the diameter, multiply the two numbers obtained. We get the same value, as it should be. Now you know how to find out the cable cross-section by diameter. Whichever of these formulas is more convenient for you, use that one. No difference.

Correspondence table of wire diameters and their cross-sectional area

It is not always desirable or possible to carry out calculations in a store or in the market. In order not to waste time on calculations or not to be mistaken, you can use the table of correspondence of diameters and cross-sections of wires, which contains the most common (standard) dimensions. You can rewrite it, print it and take it with you.

How to work with this table? As a rule, the cables have a mark or tag on which its parameters are indicated. The marking of the cable, the number of cores and their cross-section are indicated there. For example, 2x4. We are interested in the parameters of the vein and these are the numbers that stand after the "x" sign. In this case, it is stated that there are two conductors having a cross section of 4 mm 2. So we will check if this information is true.

How to work with a table

To check, measure the diameter using any of the methods described, then check with the table. It indicates that with such a cross section of four square millimeter, the wire size should be 2.26 mm. If your measurements are the same or very close (there is a measurement error, since the devices are imperfect), everything is fine, you can buy this cable.

But more often than not, the actual diameter of the conductors is much smaller than the stated one. Then you have two ways: look for a wire from another manufacturer or take a larger section. Of course, you will have to overpay for it, but the first option will require enough large gap time, and it's not a fact that you will be able to find a cable that meets GOST.

The second option will require more money, since the price depends significantly on the declared section. Although, not a fact - a good cable, made according to all standards, may cost even more. This is understandable - the cost of copper, and, often, for insulation, subject to technology and standards, is much higher. Therefore, manufacturers are cunning by reducing the diameter of the wires - in order to reduce the price. But such savings can turn into disaster. So be sure to take measurements before purchasing. Even trusted suppliers.

And one more thing: inspect and feel the insulation. It should be thick, solid, of the same thickness. If, in addition to changing the diameter, there are also problems with insulation, look for a cable from another manufacturer. In general, it is advisable to find products that meet the requirements of GOST, and not made according to TU. In this case, there is a hope that the cable or wire will serve for a long time and without problems. This is not easy to do today, but if you breed or, quality is very important. Therefore, it is probably worth looking.

How to determine the cross section of a stranded wire

Sometimes conductors are used stranded - consisting of many identical thin wires. How to calculate the cross-section of the wire by diameter in this case? Yes, exactly the same. Carry out measurements / calculations for one wire, count their number in a bundle, then multiply by this number. Here you will find out the cross-sectional area of ​​a stranded wire.

In order to successfully buy a wire, before buying it is necessary measure wire diameter otherwise you can become a victim of deception. You will also have to measure the cross-section of the wire if you add a new electrical point on the old wiring, since letter marking it may not be on it. The information below will help you choose the right technique. wire diameter measurement and use it effectively in practice.

In this case, the question immediately arises: "What is the point of the company to spoil its reputation?" There can be several explanations for this: But the whole point is that even after correct calculations wire cross-section, you may still encounter a problem, despite the fact that you buy wire with suitable diameter... An accident can occur due to the fact that the wire marking will indicate the cross-section of the wires, which does not correspond to the actual one. This can happen as a result of the manufacturing plant saving on material, or the company producing this product, all characteristics of the product have not been observed. Also on the shelves you can find wires on which there is no marking at all, which initially casts doubt on their quality.

1. In order to save money. For example, the plant made wire diameter less by only 2 mm. sq. with a 2.5 mm core, which made it possible to win on one running meter several kilograms of metal, not to mention the profit from mass production.

2. As a result of great competition, the company lowers the price of electrical wiring, trying to entice most consumers. Naturally, this is due to reducing the wire diameter, which is impossible to determine with the naked eye.

Both the first and second options have a place to be on the sales market, so you'd better play it safe and make accurate calculations yourself, about which and there will be a speech farther.

There are three main ways to determine the diameter of a wire.

There are several ways, but each of them is based on determination of diameters veins with subsequent calculations of the final results.

Method one. With the help of instruments. Today there are a number of devices that help measure wire diameter or wire strands. This is a micrometer and a vernier 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 electrical wiring. The most accurate results can be obtained with a caliper. This technique has the advantage that it is possible measure wire diameter even in a section of a working line, for example, in an outlet.

After you have measured wire diameter, it is necessary to carry out calculations according to the following formula:

It must be remembered that Pi" is 3.14, respectively, if we divide the number "Pi" by 4, then we can simplify the formula and reduce the calculations to multiplying 0.785 by the diameter squared.

Method two... We use a ruler. If you decide not to spend money on a device, which is logical in this situation, then you can use a simple proven method to measure the cross-section of a wire or wire ?. You will need a simple pencil, ruler, and wire. Strip the insulation from the core, screw it tightly around a pencil, and then measure it with a ruler total length winding (as shown in the picture).

Then divide the length of the wound wire by the number of cores. The resulting value will be wire section diameter.

However, it is necessary to consider the following:

• the more veins you wind on a pencil, the more accurate the result will be, the number of turns should be at least 15;
• press the turns tightly to each other so that there is no free space, this will significantly reduce the error;
• take measurements several times (change the side of the measurement, the direction of the ruler, etc.). A few results obtained will help you, again, to avoid a large error.

Pay attention to the disadvantages of this measurement method:

1. You can only measure section of thin wires, since the thick wire will be difficult for you to wrap around the pencil.

2. To get started, you will need to purchase a small piece of the product before making the main purchase.

The formula discussed above is suitable for all measurements.

Method three. We use the table. In order not to carry out calculations by the formula, you can use a special table in which the diameter of the wire is indicated? (in millimeters) and conductor cross-section (in square millimeters). Ready-made tables will give you more accurate results and will significantly save you time that you do not have to spend on calculations.