In order to successfully buy a wire, before buying it is necessary measure the diameter of the wire, otherwise you can become a victim of deception. You will also have to measure the wire cross section if you add a new electrical point on the old wiring, since alphabetic marking on it may not be. The information below will help you choose the right technique measuring the diameter of the wire and effectively use it in practice.
At the same time, you will immediately have the question: "What is the point of the company spoiling its reputation?" There may be several explanations for this: But the fact is that even having made correct calculations of the wire cross section, you can still face the problem, in spite of the fact that buy wire with a suitable diameter. The accident can occur due to the fact that the labeling of wires will indicate the cross-section of the cores, which does not correspond to the actual one. This can happen as a result of the fact that the manufacturer has saved on the material, or the company producing this product has not met all the characteristics of the product. Also, on the shelves, you can find wires that are completely missing markings, which initially makes one question their quality.
1. For the sake of economy. For example, a plant made wire diameter less than only 2 mm. sq. m. at 2,5-millimeter veins, which made it possible to win a kilogram of metal on one running meter, not to mention profits in mass production.
2. As a result of great competition, the company reduces the price of electrical wiring, trying to entice a large part of consumers to itself. Naturally, this is due to the reduce the diameter of the wire, which can not be determined with the naked eye.
Both the first and second option takes place in the sales market, so you better be safe and make yourself precise calculations, which will be discussed later.
The three main ways to determine the diameter of the wire.
There are several ways, but at the heart of each of them lies determination of diameters veins with subsequent calculations of the final results.
Method one. With the help of instruments. For today there are a number of devices that help measure the diameter of the wire or wires of the wire. This 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 electrical wiring. The most accurate results can be obtained with a caliper. This technique has advantages in that it is possible to measure the diameter of the wire even on the section of the working line, for example, in the socket.
After you have measured wire diameter, it is necessary to calculate by the following formula:
It must be remembered that pi" is 3.14, respectively, if we divide the number "Pi" by 4, we can simplify the formula and reduce the calculation to multiplication of 0.785 per 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, 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 vein from the insulation, tightly wind it on the pencil, and after that measure the total length of the winding (as shown in the picture).
Then, the length of the wound wire is divided by the number of strands. The value obtained will be wire section diameter.
But you should consider the following:
- the more you live on a pencil, the more accurate the result, the number of turns must be at least 15;
- tighten the threads tightly to each other, so that there is no free space between them, this will significantly reduce the error;
- take measurements several times (change the measuring side, the direction of the ruler, etc.). A few obtained results will help you again to avoid a big error.
Pay attention to the disadvantages of this method of measurement:
1. You can only measure section of thin wires , since a thick wire you will hardly be able to wind on a pencil.
2. To begin with, you will need to purchase a small piece of the product before making the basic purchase.
The formula discussed above is suitable for all measurements.
Way the third. We use the table. To avoid calculating the formula, you can use a special table in which specified wire diameter? (in millimeters) and the cross section of the conductor (in millimeters square). Finished tables will give you more accurate results and save you a lot of time, which you do not have to spend on calculations.
|
Diameter of the conductor, mm |
Conductor cross-section, mm 2 |
When buying or always paying attention to its actual section, as it is often in stores you can find cable products with a section that does not correspond to its marking, and significantly. And this, as you know, can lead to overheating of the cable and, as a result, to short circuit.
For self-calculation of the actual cross-section of the wire, several simple methods will help us. The most convenient way is to calculate the wire cross section by its diameter. To do this, you need a micrometer or calipers.
Having measured the diameter of the core, we recall the formula of the area of the circle:
For example, take a wire whose insulation indicates the BBGng marking 3 × 2.5. We measure the diameter of the vein with a caliper - we get 1.7 mm. Next, substitute this value in the formula:
Scr = 0.785 x 1.7 x 1.7 = 2.27mm2.
It turns out that the actual cross-section of the wire is 2.27mm2 instead of the declared 2.5.
With a solid wire everything is clear, but what about multicore?
Here everything is approximately the same. We take one core from the stranded wire and measure it with a caliper. For example, the diameter was 0.4 mm.
Scr = 0.785 x 0.4 x 0.4 = 0.125mm2.
Then we calculate the total number of veins in the wire, suppose 12.
And now we know the total cross-section of the wire, multiplying the value of one core by 0.125mm2 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 and the more micrometer, in this case it is necessary to go another way.
To do this, we need a ruler and a pencil, or some round rod, from improvised tools. Remove the insulation from the wire and reel about 10 turns on the rod. The main thing is that the coils fit tightly to each other, without gaps.
Ruler measure the length of the winding and divide by the number of turns. We get the diameter of the vein. And then, using the same formula, we find the cross-section of the vein. The method is quite accurate, but not very convenient - and in the store so do not measure and thick veins do not reel.
In order not to calculate the cross-section on the calculator every time, I will lay out below a table of correspondence of diameters and cross-sections of wires, in which there are the most common dimensions. You can copy it or print it and take it with you to the store. It only remains to measure the diameter of the core and compare it with the value from the table. If the measured value is significantly different from the table value, then it is better not to buy such a cable.
Instructions
Measurement diametera wires Use calipers when there is no voltage. Any caliper, regardless of whether it is mechanical or electronic, has metal sponges capable of conducting current. If the wire is covered with a layer of insulation, measure its cross-section without taking it into account diametera.
To translate the section indicated in the directory wires in his diameter, use the following formula: D = 2√ (S / π), where S is the area of the conductor (mm²), D - diameter conductor (mm), π - number "pi", 3.1415926535 (dimensionless value).
For the reverse translation ( diametera in section) use the same formula, transformed as follows: S = π (D / 2) ², where D - diameter conductor (mm), S - conductor area (mm²), π - number "pi", 3.1415926535 (dimensionless value).
Cross section of stranded wires take equal to the sum of the sections entering into it composition separate conductors. Summarize them diameters meaningless. Calculations can be multistage. For example, to find an equivalent diameter stranded wires, calculate the cross section of one of its veins, multiply by their quantity and then translate the result again into diameter.
Take the wire from diameteror cross-section exceeding the calculated or specified in the table value, you can, but too thick wires use it happens inconvenient: they can, for example, pull the terminal from the terminal block by its own weight. Apply the same wires from diameteror section is less than the calculated or specified in table it is impossible.
Hollow conductors of cylindrical shape (for example, included in the composition of coaxial cables) have two diametera: external and internal. For them, calculate, respectively, two sections: external and internal. Subtract one from the other, and then translate the result into an equivalent diameter.
Clean from the insulation of the cable core. Using a caliper, and preferably a micrometer (this will allow a more accurate measurement), find the diameter of the core. The value will be in millimeters. Then calculate the cross-sectional area. For this, multiply the coefficient by 0.25 by the number π≈3.14 and the diameter value d squared S = 0,25 ∙ π ∙ d². Multiply this by the number of wires. Knowing the length of the wire, its cross section and the material from which it is made, calculate its resistance.
For example, if you want to find a section of a copper cable of 4 cores, and measure the diameter of the core, give a value of 2 mm, find the area of its cross-section. To do this, calculate the cross-sectional area of one core. It will be equal to S = 0,25 ∙ 3,14 ∙ 2² = 3,14 mm². Then determine the cross section of the entire cable for this cross section of one core multiply by their number in our example it is 3.14 ∙ 4 = 12.56 mm ².
Now you can find out the maximum current that can flow through it, or its resistance, if the length is known. The maximum current for a copper cable is calculated from a ratio of 8 A per 1 mm². Then the limiting value of the current that can pass through the cable taken in the example is 8 ∙ 12.56 = 100.5 A. Note that for aluminum cable this ratio is 5 A per 1 mm².
For example, the length of the cable is 200 m. In order to find its resistance, multiply the resistivity of copper ρ in Ohm ∙ mm² / m, by the cable length l and divide by its cross-sectional area S (R = ρ ∙ l / S). After making the substitution, you will get R = 0,0175 ∙ 200 / 12,56≈0,279 Ohm, which will lead to very small losses of electricity when it is transmitted over such a cable.
Sources:
- how to find the cable section
Often find the right the wire to connect a particular device is problematic, given their total number in the hardware configuration of a modern computer.
Instructions
If you need to find the wire connection of the monitor to the video card, pay attention to a thick cable with a diameter of about 1 centimeter with two similar wide plugs at both ends of blue or white. White plugs are used to connect the monitor to the digital output from the video card, and blue - to the analog.
To determine exactly what you need, pay attention to the presence of connectors in the devices. If your monitor or video card is supported one at a time, but different connection interfaces, which is very rare, use a special DVI-VGA adapter, which usually comes with a computer or a monitor.
Imagine that you found in your bins an old electrical cable that you want to use. But before you is the problem of determining its cross-section. By the eye it can not be determined, the tag, of course, does not remain on it. What to do? There are several ways in which the core diameter lies. That is, the diameter of the wire and the cross section are directly dependent on each other, which is the confirmation of the circle formula, because the cross-sectional shape of the wire is a circle. Here's the formula:
S = 3.14d² / 4 = 0.785d².
Therefore, we must first determine the diameter of the vein.
Method number 1
To do this you will need a caliper. It is simply necessary to clean the core of the insulation and measure the diameter. Then the value obtained is substituted into the circle formula. Here you have the cross-sectional area of the wire.
Let's just say that this option is the simplest and most accurate. Therefore, it is worthwhile in the arsenal of an electrician to keep this measuring tool.
Method number 2
It can be used in case there is no caliper at hand. The process of determining this is not easy and requires a certain accuracy of all its stages. So, here you need either a pencil, or a pen, or a screwdriver, or any tube of dense material (better metal). Here is the algorithm of actions:
- The insulation is removed in a length of centimeters twenty-thirty.
- Now we wind the wire on a pencil or other object, as described above. The more turns you make, the more accurate the metric. At the same time wind the windings so that they are tightly pressed against each other.
- It is counted the number of turns.
- The length of twisted turns is measured with the help of a conventional ruler, that is, using a pencil from the first to the last.
- Now it is necessary to carry out one mathematical action - to divide the length of the turns into their number. This will be the diameter of the wire.
Of course, it is not the most accurate, because everything will depend on how the cable vein was wound. Here, as was said above, the density of turns is of primary importance. Now you can substitute the diameter of the wire in the formula of the area of the circle.
Method number 3
This method relates to determining the cross-section of a wire along the diameter of a stranded wire. In fact, all of the above methods are suitable for this option, only with one condition. You need a vein, if I may say so, to fluff. Select one wire and measure its diameter with a caliper or use a pencil. After that, the value obtained must be multiplied by the number of procrastinations, which can not be counted very easily. This is the diameter of the core, which is substituted into the cross section formula.
Method number 4
This is the so-called tabular method, that is, to determine the area of the cable you will need a table, which indicates the main parameters of the product. Such a table is also on the Internet, so you should not have any problems finding it. You can refer to the tables PUE, which also describes the parameters and indicators of electrical cables.
Why you need to know the wire cross section
Everyone knows that the thicker the wire, the more current loads it withstands, the more power it can connect to household appliances. Therefore, the cross-section of the cable is the main characteristic that will help to avoid unpleasant moments associated with overheating of electrical wiring, and, accordingly, the occurrence of fires.
There are certain standards in which it is stipulated which section (diameter) of the wire should be installed under the necessary current loads. These standards are defined by the rules for the management of electrical installations (PUE), where tables are present. They clearly arranged positions related to the area, the material from which the wires are made, and the current load or the power consumption.
But there is one very subtle point that a buyer should know. There are electrical wires that are manufactured according to technical specifications (TU), there are manufactured according to state standards (GOST). Their differences consist in the fact that products manufactured according to the specifications sometimes have a smaller diameter of the vein (ten to thirty percent), and, accordingly, a reduced cross-section. And this is the reason for reducing the current load that the cable can pass through itself. Plus, the insulation is made more thin layer. To what it can lead, probably, you guess.
Therefore, the recommendation: if you choose an electrical wiring made according to specifications, it is recommended to choose its cross section an order of magnitude higher. For example, according to calculations, a 1.5 mm² cable is required, it is better to choose 2.5 mm². In reality, this figure will be an area of 1.8-2.0 mm².
How do you know by what standards the wire was manufactured?
- First, it must be indicated in the product quality certificate.
- Secondly, you can check the insulation. If it is soft and quickly removed from the vein, then this is uniquely material made according to the specifications.
- Third, measure the diameter of the wire with a caliper. And then, using the formula of the circle, calculate the area of the vein. In principle, it can be done on a cell phone calculator, that is, right in the store. If the calculated value corresponds to the nominal value, then this is the ghost material. If the value is lower, then this wire is made according to specifications.
Conclusion on the topic
As you can see, there are several ways how you can learn and determine the wire cross-section by the diameter of the core. The simplest is number one. But in this case you will need a caliper. If you have Internet at hand, you can use the world wide web. That is, everyone chooses what is convenient for him at a certain point in time.
Similar entries: