How to determine the cross-section of a welding cable. How to determine the cross-section of cable and wire? A simple method for determining diameter
When purchasing, you should always pay attention to its actual cross-section, since you can often find cable products in stores with a cross-section that does not correspond to its marking, and significantly so. And this, as you understand, can lead to overheating of the cable and ultimately to a short circuit.
To independently calculate the actual wire cross-section, several help us: simple ways. The most convenient way is to calculate the cross-section of the wire based on its diameter. To do this you will need a micrometer or caliper.
Having measured the diameter of the core, we recall the formula for the area of a circle:
For example, let’s take a wire whose insulation is marked VVGng 3×2.5. We measure the diameter of the core with a caliper - we get 1.7 mm. Next, we substitute this value into the formula:
Skr = 0.785 x 1.7 x 1.7 = 2.27 mm2.
It turns out that the actual cross-section of the wire is 2.27 mm2 instead of the stated 2.5.
Everything is clear with a single-core wire, but what about multi-core?
Everything is about the same here. We take one core from a stranded wire and measure it with a caliper. For example, the diameter turned out to be 0.4 mm.
Skr = 0.785 x 0.4 x 0.4 = 0.125 mm2.
Then we count the total number of veins in the wire, suppose 12.
Now we find out the total cross-section of the wire by multiplying the value of one core 0.125 mm2 by the number of cores - 12.
S = 0.125 x 12 = 1.5mm2- this is the actual cross-section of the wire.
Of course, not everyone has a caliper, much less a micrometer, in which case you will have to go another way.
To do this, we will need a ruler and a pencil, or some kind of round rod, from available means. We remove the insulation from the wire and wind about 10 turns onto the rod. The main thing is that the turns fit tightly to each other, without gaps.
Using a ruler, measure the length of the winding and divide by the number of turns. We get the diameter of the core. And then, using the same formula, we find the cross-section of the core. The method is quite accurate, but not very convenient - and you can’t measure it in a store this way and you can’t wind thick wires.
In order not to calculate the cross-section each time on a calculator, below I will post a table of the correspondence of diameters and cross-sections of wires, which contains the most common sizes. You can rewrite it or print it out and take it with you to the store. All that remains is to measure the diameter of the core and compare it with the value from the table. If the measured value differs significantly from the table, then it is better not to buy such a cable.
When installing electrical wiring, it is necessary to determine the power of consumers in advance. This will help in the optimal selection of cables. This choice will allow you to operate the wiring for a long time and safely without repairs.
Cable and conductor products are very diverse in their properties and intended purpose, and also have a wide range in prices. The article talks about the most important wiring parameter - the cross-section of a wire or cable in terms of current and power, and how to determine the diameter - calculate it using a formula or select it using a table.
The current-carrying part of the cable is made of metal. The part of the plane passing at right angles to the wire, bounded by metal, is called wire cross-section. The unit of measurement is square millimeters.
Section determines permissible currents passing through wires and cables. This current, according to the Joule-Lenz law, leads to the release of heat (proportional to the resistance and the square of the current), which limits the current.
Conventionally, three temperature ranges can be distinguished:
- the insulation remains intact;
- the insulation burns, but the metal remains intact;
- metal melts at high temperatures.
Of these, only the first is the permissible operating temperature. In addition, with a decrease in cross-section its electrical resistance increases, which leads to an increase in voltage drop in the wires.
However, an increase in cross-section leads to an increase in mass and especially cost or cable.The materials used for the industrial production of cable products are pure copper or aluminum. These metals have different physical properties, in particular, resistivity, therefore the cross sections selected for a given current may turn out to be different.
Find out from this video how to choose the right wire or cable cross-section according to power for home wiring:
Determination and calculation of cores using the formula
Now let’s figure out how to correctly calculate the cross-section of a wire based on power, knowing the formula. Here we will solve the problem of determining the section. It is the cross section that is the standard parameter due to the fact that the nomenclature includes both single-core and multi-core options. The advantage of multi-core cables is their greater flexibility and resistance to kinks during installation. As a rule, stranded wires are made of copper.
The easiest way to determine the cross-section of a round single-core wire is d– diameter, mm; S– area in square millimeters:
Stranded ones are calculated by a more general formula: n– number of veins, d– core diameter, S- square:
The current density is determined very simply, it is number of amperes per section. There are two wiring options: open and closed. Open allows a higher current density due to better heat transfer in environment. Closed requires a downward adjustment so that the heat balance does not lead to overheating in the tray, cable duct or shaft, which can cause a short circuit or even a fire.
Accurate thermal calculations are very complex; in practice, they are based on the permissible operating temperature of the most critical element in the structure, according to which the current density is selected.
Thus, the permissible current density is the value at which heating of the insulation of all wires in a bundle (cable duct) remains safe, taking into account the maximum ambient temperature.Table of current cross-section of copper and aluminum wire or cable:
Table 1 shows the permissible current density for temperatures not higher than room temperature. Most modern wires have PVC or polyethylene insulation, allowing heating during operation no more than 70-90°C. For “hot” rooms, the current density must be reduced by a factor of 0.9 for every 10°C to the operating temperatures of the wires or cables.
Now about what is considered open and what . is wiring if it is made with clamps (tires) along the walls, ceiling, along the supporting cable or through the air. The closed one is laid in cable trays, walled into walls under plaster, made in pipes, a shell or laid in the ground. You should also consider the wiring closed if it is in or. The closed one cools worse.
For example, let the thermometer in the dryer room show 50°C. To what value should the current density of a copper cable laid in this room along the ceiling be reduced if the cable insulation can withstand heating up to 90°C? The difference is 50-20 = 30 degrees, which means you need to use the coefficient three times. Answer:
Example of calculating the wiring section and load
Let suspended ceiling is illuminated by six lamps with a power of 80 W each and they are already connected to each other. We need to supply power to them using aluminum cable. We will assume that the wiring is closed, the room is dry, and the temperature is room temperature. Now we’ll find out how to calculate the power of copper and aluminum cables; for this we use the equation that determines the power (according to the new standards, we consider the mains voltage to be equal to 230 V):
Using the corresponding current density for aluminum from Table 1, we find the cross-section required for the line to operate without overheating:
If we need to find the diameter of the wire, we use the formula:
Suitable would be cable APPV2x1.5 (section 1.5 mm.kv). This is perhaps the thinnest cable you can find on the market (and one of the cheapest). In the above case, it provides a double power reserve, i.e. a consumer with a permissible load power of up to 500 W, for example, a fan, dryer or additional lamps, can be installed on this line.
It is unacceptable to install sockets on this line, since they may (and most likely will) contain a powerful consumer and this will lead to overloading the line section.Quick Selection: Useful Standards and Ratios
To save time, calculations are usually tabulated, especially since the range of cable products is quite limited. The following table shows the calculation of the cross-section of copper and aluminum wires according to power consumption and current strength, depending on the purpose - for open and closed wiring. The diameter is obtained as a function of load power, metal and type of wiring. The mains voltage is considered to be 230 V.
The table allows you to quickly select a section or diameter, if the load power is known. The found value is rounded up to the nearest value from the nomenclature series.
The following table summarizes the data on permissible currents by cross-section and power of materials of cables and wires for calculation and quick selection of the most suitable ones:
The wiring arrangement, among other things, requires design skills, which not everyone who wants to do it has. It is not enough to just have good electrical installation skills. Some people confuse design with drawing up documentation according to some rules. These are completely different things. Nice project can be written on pieces of paper from a notebook.
First of all, draw a plan of your premises and mark future sockets and lamps. Find out the power of all your consumers: irons, lamps, heating devices, etc. Then enter the power of the loads most frequently consumed in different rooms. This will allow you to choose the best cable options.
You will be surprised how many possibilities there are and what is the reserve for saving money. Once you select , count the length of each line you draw. Put everything together, and then you will get exactly what you need, and as much as you need.
Each line must be protected by its own (), designed for a current corresponding to the permissible power of the line (the sum of the consumer powers). Sign the machines, located in, for example: “kitchen”, “living room”, etc.
It is advisable to have a separate line for all lighting, then you can easily repair the socket in the evening without using matches. It is the sockets that are most often overloaded. Provide outlets with enough power - you don't know in advance what you'll have to plug into them.In damp rooms, use only double-insulated cables! Use modern sockets (“Euro”) and with grounding conductors and connect the grounding correctly. Bend single-core wires, especially copper ones, smoothly, leaving a radius of several centimeters. This will prevent them from breaking. Wires must lie straight in cable trays and ducts, but freely, in no case should you pull them like a string.
There should be a margin of a few extra centimeters. When laying, you need to make sure that there are no sharp corners anywhere that could cut the insulation. The terminals must be tightened tightly when connecting., and for stranded wires this procedure should be repeated; they have a tendency for the cores to shrink, as a result of which the connection may become loose.
Copper wires and aluminum wires are not “friendly” with each other for electrochemical reasons; they cannot be connected directly. To do this, you can use special terminal blocks or galvanized washers. The joints must always be dry.Phase conductors must be white (or brown), and neutrals must always be blue. Grounding is yellow-green in color. These are generally accepted color rules and commercial cables, as a rule, have internal insulation in exactly these colors. Compliance with colors increases the safety of operation and repair.
We bring to your attention an interesting and educational video on how to correctly calculate the cable cross-section by power and length:
The choice of wire cross-section is the main element of a power supply project of any scale, from a room to large networks. The current that can be taken into the load and power will depend on this. Right choice wires also ensure electrical and fire safety, and provides an economical budget for your project.
You can often find electrical products in supermarkets without tags or identification marks. Among it there could easily be a coil of wire or cable. How do you know if the wire size is appropriate for your specific situation? The answer is simple - measure it or consult the seller.
Anyone who sells cables and wires can tell you what load they can withstand. In addition, inscriptions (numbers) are stamped on the wires, characterizing the cross-section and number of cores. But in real practice, not everything is as simple as it seems. The quality of cable products has recently deteriorated noticeably.
Problems with the quality of manufactured wires
Many manufacturers of cable and wire products, trying to make more money, artificially reduce the thickness of the insulation and increase the diameter of the cable.
By specifying a larger wire cross-section than in reality, the manufacturer saves a very large amount. For example, to produce thousands of meters of copper wire with a cross-section of 2.5 mm2, 22.3 kg of copper is required, and to produce a wire of 2.1 mm2, only 18.8 kg is required. This results in a saving of 3.5 kg of copper.
Another way to reduce the cost of products is to manufacture a conductor from low-quality raw materials. When adding cheap impurities, the current conductivity decreases, therefore, cable length calculations must be changed.
Why do you need to calculate the cable load? This question often arises when installing wiring in an apartment or home. First, all planned loads are considered, and then the required wire cross-section is determined.
Then the necessary material is purchased from the store and electrical wiring is installed in the house.
As a result of using new wiring, the circuit breaker on the electrical panel first “knocks out”, and then damage to the wire is discovered. Moreover, it often turns out to be completely melted, as a result of which a short circuit occurs. It turns out that the calculations were made incorrectly, and how can you find out the minimum permissible value of the wire cross-section in this case? household appliances, which are usually used at home when preparing food and creating our comfort, can be distinguished:
- electric stove;
- air conditioner;
- microwave;
- electric kettle;
- iron;
- washing machine and dishwasher;
- coffee grinder;
- vacuum cleaner.
Power consumption of this household appliances ranges from 1 to 2 kilowatts (except for electric stoves).
Important! If the cross-section of the wire is indicated incorrectly (underestimated), then when using it, it is natural for large overloads to occur, which lead to a fire in the wiring.
How to calculate?
Experienced electricians can “by eye” determine the wire cross-section with great accuracy. This is much more difficult for an ordinary person to do. Therefore, it is best to calculate the cable cross-section by diameter right in the store. At least it will be much cheaper than eliminating the consequences of a short circuit due to an overload in the electrical network.
Let's try to do this with specific examples using arithmetic formulas in school mathematics.
Everyone roughly understands what a wire cross-section is. If you bite it across with wire cutters, you can see the round cross-section of a copper or aluminum core. It is measured using a standard mathematical formula: as the area of a circle. Where r is the radius of the circle, squared and multiplied by the constant “pi” (π=3.14).
The larger the diameter of the cable/wire, the greater the current that can pass through a certain amount of time. And, accordingly, the more energy consumed by electrical appliances, the larger the cross-section of the wire should be.
From the simplified formula Scr = 0.785d2 it is clear that to calculate the cross-sectional area you need to know the exact diameter of the wire. To do this, it is necessary to remove the insulation from the core.
Calculation for stranded wire
Stranded wire (stranded) consists of single-core wires twisted together. Anyone who is even a little familiar with mathematics understands perfectly well that it is necessary to count the number of these wires in a stranded wire. After this, the cross-section of one thin wire is measured and multiplied by their total number. Let's consider the following options.
Calculation using a caliper
The measurement is carried out with a caliper with a conventional scale (or micrometer). Experienced craftsmen always have this tool at hand, but not everyone is a professional electrician.
To do this, using the VVGng cable as an example, cut the thick sheath with a knife and spread the wires in different directions.
Then select one core and strip it with a knife or scissors. Next, measure this core. The size should be 1.8 mm. Please refer to the calculations to prove the measurement is correct.
The resulting figure of 2.54 mm2 is the actual cross-section of the core.
Measuring with a pen or pencil
If you don’t have a caliper at hand, you can use improvised methods using a pencil and ruler. First, take the wire to be measured, strip it and wind it around a pencil or pen so that the turns lie close to each other.
The more turns, the better. Now let's count the number of wound turns and measure their total length.
For example, we got 10 turns with a total winding length of 18 mm. It is easy to calculate the diameter of one turn; to do this, divide the total length by the number of turns.
As a result of all the calculations made using the formula, you will obtain the required diameter of the core. In this case it is 1.8 mm. Since the diameter of one core is known, it is not difficult to calculate the cross-section of the entire VVGng wire using the already known formula.
You can see that the results were equal.
Using tables
How can you find out and measure the cable cross-section if you don’t have a caliper, a ruler, or a micrometer at hand? Instead of racking your brains over complex mathematical formulas, just remember that there are ready-made tables of values for measuring cable cross-section. There are, of course, very complex tables with many parameters, but, in principle, to begin with it is enough to use the simplest of the two columns. The diameter of the conductor is entered in the first column, and the ready-made values of the wire cross-section are given in the second column.
Wiring cross-section table for closed wiring
Let's say 2.5 mm2. You buy a cable or wire and install the wiring. After some time, the line is suddenly damaged. The channel is opened and it turns out that the insulation of the wires has melted. If the cross-section does not correspond to the load, such a situation is simply inevitable.
The reason for this could be:
- incorrect calculation and selection of wire cross-section;
- absence of technical information on the wire packaging or its unreliability.
Incorrect definition of the section can lead to negative consequences. It is super important to be able to correctly calculate section parameters. This way you can avoid unpleasant situations and save a decent amount.
Today the editors tell you how to find out the wire cross-section. Bonus - we have compiled several calculation options so that everyone can choose the best one for themselves.
How to determine wire cross-section: 3 main methods
Calipers
Pencil + ruler
Table
Option number 1: find out the wire cross-section using a caliper
Figure 1 - The wire has a mark and section. It happens that the cable is defective, that is, truncated. For example, you need a VVG 3x2.5, but in fact 3x2.1, although it says 3x2.5To determine the cross-section or triangular cross-section of a wire and cable core, a caliper is used. Below is an example of calculations using the device.
To get started, recall the formula for determining the area of a circle:
where n=3.14; r is the radius of the circle.
We will use a simplified version of the formula, adapted to our case:
d – diameter of the circle (core).
For clarity, divide the number n by 4. The result is the formula:
We determine the diameter of the wire: this is how we find out the cross-sectional area. To do this, you need to clean the wire core. Then measure its diameter using a caliper.
The result was 1.78 mm. This number must be put into the expression. Eventually:
Let's round to hundredths and get a wire cross-section of 2.79 mm2.
Option No. 2: determine the wire cross-section using a pencil and ruler
Not everyone has special equipment at home. And buying it for one-time use is stupid. We tell you how to determine the cross-section without professional instruments.
We take the wire and strip it along its length. 30-50 cm is enough. Then we wrap the wire around a pen or pencil. You need to wind them tightly to each other. Then we count the number of turns obtained and measure the length. Let's say we get 19 turns with a total length of 32 mm.
To find out the diameter, you need to divide the length by the number of turns. In our case, 32:19 = 1.684. According to the principle given in the first option, we substitute the diameter into the formula. We got 2.23 mm squared.
How accurate is this method? The magnitude of the error will depend on the number of turns: the more there are, the smaller the error.
IMPORTANT! This measurement option is not suitable for industrial scale, however, for home use it is what you need.
Option No. 3: determine the wire cross-section using the table
You can also use PUE compliance tables. They simplify the work, as they indicate the long-term permissible currents for copper and aluminum wires. This takes into account the types of insulation and shell.
Below is a simplified table for ease of use. With its help, you can determine the cross-section of three-wire, four-wire, and five-wire wires under single-phase and three-phase loads (220 V/380 V). To do this, it is enough to know the load current and its power.
- In the air (trays, boxes, voids, channels)
| Current, A | 220 V | 380 V |
|---|---|---|
| 19 | 4,1 | 12,5 |
| 25 | 5,5 | 16,4 |
| 35 | 7,7 | 23 |
| 42 | 9,2 | 27,6 |
| 55 | 12,1 | 36,2 |
| 75 | 16,5 | 49,3 |
| 95 | 20,9 | 62,5 |
| 120 | 26,4 | 78,9 |
| 145 | 31,9 | 95,4 |
| 180 | 39,6 | 118,4 |
| 220 | 48,4 | 144,8 |
| 260 | 57,2 | 171,1 |
| 305 | 67,1 | 200,7 |
| 350 | 77 | 230,3 |
| Current, A | 220 V | 380 V |
|---|---|---|
| - | - | - |
| 19 | 4,1 | 12,5 |
| 27 | 5,9 | 17,7 |
| 32 | 7 | 21 |
| 42 | 9,2 | 27,6 |
| 60 | 13,2 | 39,5 |
| 75 | 16,5 | 49,3 |
| 90 | 19,8 | 59,2 |
| 110 | 24,2 | 72,4 |
| 140 | 30,8 | 92,1 |
| 170 | 37,4 | 111,9 |
| 200 | 44 | 131,6 |
| 235 | 51,7 | 154,6 |
| 270 | 59,4 | 177,7 |
- In the ground
| Current, A | 220 V | 380 V |
|---|---|---|
| 27 | 5,9 | 17,7 |
| 38 | 8,3 | 25 |
| 49 | 10,7 | 32,5 |
| 60 | 13,2 | 39,5 |
| 90 | 19,8 | 59,2 |
| 115 | 25,3 | 75,7 |
| 150 | 33 | 98,7 |
| 180 | 39,6 | 118,5 |
| 225 | 49,5 | 148 |
| 275 | 60,5 | 181 |
| 330 | 72,6 | 217,2 |
| 385 | 84,7 | 253,4 |
| 435 | 95,7 | 286,3 |
| 500 | 110 | 329 |
| Current, A | 220 V |
|---|---|
Input wire cross-section: how to find out?
IMPORTANT! Introductory value circuit breaker must be approved by the energy supply institution. Without this procedure, it is prohibited to change it, because this may affect the selectivity of the operation of protection devices located in the power circuit in the ASU/TP (including the allocated power for a specific housing).
You can find out the denomination parameters in two ways:
- in an organization specializing in energy saving;
- in the documentation where technical specifications to join networks.
For clarity, let’s take the conditional values of technical specifications. For example, power - 5 kW, nominal input machine— 25 A and single-phase power supply (220 V).
It's simple. It is necessary to take into account the type of electrical wiring, the material used for the production of cores and the voltage. We select the cross-section so that the long-term permissible current of the cable is higher than the rating of the input circuit breaker.
For example, we decided to install the input cable into the house with a three-core copper VVGng brand, laying it open method. Therefore, the suitable cross-section will be no less than 4 mm2, which means that you need to buy VVGng (3x4).
Remember about the “conditional shutdown current” of the machine: a machine that provides a rated current of 25 A has a “conditional shutdown current” of 1.45 25 = 36.25 A.
In such conditions, the machine will turn off in a cold state after about an hour.
A cable with a cross section of 4 mm2 has a continuous permissible current of 35 A, the “conditional shutdown current” indicator is 36.25 A. The values do not differ much, you don’t have to change anything. However, it is better to choose a 6 mm2 input cable with a continuous current rating of 42 A.
How to determine what cross-section of the wire of the outlet lines?
Every electrical appliance has power. The parameters can be found in the product passport or on the sticker supplied by the manufacturer. It is measured in Watts. As an example, we will offer conditional parameters.
Let's say you need a supply line for washing machine. The power of the device is 2.4 kW. We use a copper three-core cable of the VVGng brand, lay it so that it is not visible. From this we conclude that the cross-section should be at least 1.5 mm2. This means that you will need a VVGng cable (3x1.5).
If you use the outlet only to connect the washing machine, these parameters will be sufficient. To protect the cable you will need a machine with a rated current of 10 A.
However, sockets are rarely installed for such reasons. For example, you will need to connect another device to the same network, and each electrical device has its own power. It is more advisable to use a copper cable with a cross-section of 2.5 mm2 for outlet lines. For protection, you need to install a circuit breaker with a rating of 16 A.
How to find out the wire cross-section of a three-phase motor?
Let's assume there is a three-phase asynchronous motor of type AIR71A4U2. Its power is 550 W, and the windings are connected in a star at a voltage of 380 V. To find out which cross-section will be optimal, you need to look at the rated current of the motor, which is indicated on the sticker of the device. Let's say it is 1.6 A.
IMPORTANT! Sometimes it happens that there is no sticker. Then you can look up the data in lookup tables. We will use copper cable and lay it over the air. To determine the cross section, refer to the table. We get 1.5 mm2. It can also be recognized by the power of the consumer.
Depending on the situation, you can choose the most convenient method. They say that experienced electricians are able to determine the cross-section visually by eye. But for now, we advise beginners to refrain and still use our recommendations. Good luck!
When installing electrical wiring, it is necessary to ensure that the actual cross-section of the conductor corresponds to that specified in the project. Since this parameter determines the resistance to electric current, and if there is a discrepancy, overheating and a risk of fire will occur. In practice, there are situations when the purchased wire is not marked at all or the electrician has doubts about the compliance of the declared characteristics with the actual ones. In this case, you need to know how to determine the cross-section of the wire at the work site.
Why does the discrepancy occur?
Despite the fact that in the conditions of modern competition, manufacturers are doing their best not to lose their customers, some of them resort to deception. To do this, they save metal by reducing the diameter. It is enough to remove just a couple of square millimeters, and over hundreds of kilometers of cable this will pay off with a significant reduction in cost.
And then the price will be reduced for the buyer, and they themselves will be satisfied. But the consumer ultimately puts himself at risk due to the fact that the conductor resistance is much lower than stated. And in the place where such a wire is laid, there is a risk of fire.
Methods for determining wire cross-section step by step
There are several ways to measure the cross-section by core diameter. If the wire is single-core, then measurements will be made immediately on it, but one conductor must be untangled from the cable coil. After this, it is cleared of insulation so that only metal remains.
Rice. 1: Removing the insulation from the wireTo calculate the area of a circle through the radius, use the formula: S = π × R 2, where:
- π – constant equal to 3.14;
- R – radius of the circle.
But, due to the fact that from a practical point of view it is much easier to calculate a diameter equal to two radii, the calculation formula will take the following form: S = π × (D/2) 2.
Rice. 2: Wire diameter Depending on the methods for measuring the diameter, such methods for calculating the cross section are distinguished.
By diameter using a caliper or micrometer
The most relevant option to measure the diameter are instruments such as calipers and micrometers. These devices allow you to measure the diameter as accurately as possible. To do this you will need a wire and a micrometer
Rice. 3: Wire and micrometer Consider an example of determining the cross-section for a single-core wire (Figure 4).
Rice. 4: Micrometer measurement To do this, latch B is moved to the open position. The micrometer handle is unscrewed to such a distance that the wire easily fits in the space between probes A. Then, using handle G, the device is twisted until the ratchet operates. After this, readings are recorded on all three scales at point B.
IN in this example the diameter is 1.4 mm, therefore, to calculate the cross-section, you need S = 3.14 × 1.4 × 1.4 / 4 = 1.53 mm 2. The same procedure for determining the cross section can be performed using a caliper.
The advantage of this method is the ability to measure any round conductor, even if it is already installed and used to power any electrical device. The main disadvantage of the method is the high cost of the devices; naturally, purchasing them for a couple of measurements is completely impractical.
By diameter using a pencil or pen
This method of determining the cross-section is based on the fact that the wire has the same diameter along its entire length. Take a regular pencil, pen or felt-tip pen and wrap the wire around it in a spiral. To eliminate the thickness of the insulation, it must be cut along its entire length. The rings should be placed as tightly as possible; the larger the space between the rings, the lower the accuracy.
Rice. 5: Defining the section with a pencil Since all wires have the same thickness, to determine the diameter of the copper wires, measure the length of the entire winding and divide by the number of turns. In this example, D = 15 mm / 15 turns = 1 mm, respectively, using the same calculation formula, we obtain a section S = 3.14 × 1 × 1 / 4 = 0.78 mm 2. Note that the more turns you make, the more accurately you determine the cross-section.
It is worth noting that the advantage of this method is that only available means can be used to determine the cross-section. The disadvantage is low accuracy and the ability to wind only thin conductors. In the example, a relatively thin wire was used, but the distance between the turns is already visible. Because of which the accuracy leaves much to be desired, it goes without saying that aluminum wire cannot be bent in this way.
By diameter using a ruler
Let’s immediately make a reservation that for measuring with a ruler you can only take a relatively thick wire; the smaller the thickness, the lower the accuracy. The diameter of the vein can be determined by thread or paper; the second option is the most preferable, as it gives greater accuracy.
Rice. 6: Preparing paper for measuring Tear off a small strip and fold it over on one side. Thinner paper is preferable, so there is no need to fold the sheet several times.
Figure 7: Paper wrapping Then the paper is applied to the wire and wrapped around the circumference until the strip touches. At the point of contact, it is bent a second time and applied to the ruler for measurement.
Figure 8: Measuring with a ruler Using the resulting circumference L, the vein diameter D = L / 2 π is found, and the cross section is calculated as shown earlier. This method section determination is well suited for large aluminum conductors. But the accuracy in this method is the lowest.
By diameter using ready-made tables
This method is suitable for standard gauge wires. For example, you have already determined the diameter using one of the above methods. Then you use the table to determine the section.
Table 1: determination of cross-section through wire diameter
|
For example, if your diameter is 1.8 mm, then this means that the cross-section according to the table will be equal to 2.5 mm 2.
By power or current
If the conductivity of the core is known, then the cross-section can be determined using it. To do this, you will need one of the parameters of the conductor - current or power. The same can be done if you can calculate the load. Then you must select the appropriate option from the tables below. But it is necessary to take into account whether the wire is made of aluminum or copper conductors.
Table 2: to select the cross-section of the copper wire, depending on the current consumed
| Maximum rated current, A | 1,0 | 2,0 | 3,0 | 4,0 | 5,0 | 6,0 | 10,0 | 16,0 | 20,0 | 25,0 | 32,0 | 40,0 | 50,0 | 63,0 |
| Standard cross-section of copper wire, mm 2 | 0,35 | 0,35 | 0,50 | 0,75 | 1,0 | 1,2 | 2,0 | 2,5 | 3,0 | 4,0 | 5,0 | 6,0 | 8,0 | 10,0 |
| Wire diameter, mm | 0,67 | 0,67 | 0,80 | 0,98 | 1,1 | 1,2 | 1,6 | 1,8 | 2,0 | 2,3 | 2,5 | 2,7 | 3,2 | 3,6 |
Table 3: to select the cross-section of copper wire, depending on power consumption
Table 4: to determine the cross-section of aluminum wire cores
| Wire diameter, mm | 1,6 | 1,8 | 2,0 | 2,3 | 2,5 | 2,7 | 3,2 | 3,6 | 4,5 | 5,6 | 6,2 |
| Wire cross-section, mm 2 | 2,0 | 2,5 | 3,0 | 4,0 | 5,0 | 6,0 | 8,0 | 10,0 | 16,0 | 25,0 | 35,0 |
| Maximum current at long-term load, A |
14 | 16 | 18 | 21 | 24 | 26 | 32 | 38 | 55 | 65 | 75 |
| Maximum load power, kilowatt (kW) |
3,0 | 3,5 | 4,0 | 4,6 | 5,3 | 5,7 | 6,8 | 8,4 | 12,1 | 14,3 | 16,5 |
For example, if, when installing electrical wiring made of aluminum, you know that the maximum current that the wire can carry under long-term load is 21 A, then to select the cross-section you need to look at the line above - 4 mm 2.
Calculation of the cross-section of a stranded wire
If stranded wire is used, in which all conductors are the same, the total cross-section is determined by adding the area of all. For example, measure the size for one core using any of the above methods. After which the actual cross-section is determined by the formula S o = n × S i, where
- S o is the total cross-section of the entire conductor;
- n – number of conductors of the same diameter;
- S i – cross-section of one wire.