Not knowing how to calculate the cross-section of the wire, an electrician will not be able to perform even the most basic electrical work. To choose the right wiring, he needs to know certain parameters and load. For example, what wire cross-section is needed for 5 kW can be understood only with certain knowledge. Illiterately chosen section can lead to rather disastrous consequences, ranging from the failure of the line itself and ending with its fire.
Content
- Settlement procedure
- Calculation using a formula
- Diameter table and their cross-sectional area
A fairly common example, when your wiring suddenly breaks down, and when you open the channel, you can see that the insulation has melted and the wire itself has burned out. This happens only in two cases:
- the section was calculated incorrectly;
- inaccuracy or lack of information about the conductor.
Settlement procedure
In order to determine the cross-section of the wire, you must first measure its diameter. For this we need a caliper or micrometer. Since we are directly interested in the circumference of the conductor itself, it will first be necessary to strip it of insulation. If during the purchase you are not allowed to do this, then you can purchase
minimum allowable a piece, and then carry out the following manipulations.When the required parameter is measured, it will be already easy to calculate the section itself. If you are interested in the question of what is preferable to make a measurement, then, we can say that the higher the measurement accuracy, the more accurate the final result will be.
There are situations when there is simply no caliper or micrometer available. In this case, we will be able to make the appropriate measurements with the help of a simple ruler. But here it may become necessary to buy test piece, since it will take 10-15 centimeters to clear of insulation, and it is unlikely that they will be allowed to do this for free.
As soon as the wire is freed from insulation, it should be wound around the cylindrical part of the screwdriver. Pay attention that the turns fit as tightly as possible to each other, leaving no gaps. The ends from the edges should be brought out to one side so that the resulting turns have a finished shape. As for the number of turns, this is not important, although it is better to do them 10, as it will be easier to calculate.
It remains only to measure and calculate directly the thickness of our wire. To do this, we measure the length of the turns used. Further, this value is divided by the number of turns - the result obtained will be the desired diameter. Let's take 10 turns as an example. The length of all these ten turns is 6.8 mm. Therefore, 6.8 divided by 10, we get 0.68. It is this value that is the desired result. With this data, you can search and direct section.
Calculation using a formula
When we have found out what the diameter of the wire is, we can proceed directly to determining its cross section. It is understood that the wire is circular in diameter. Therefore, for the calculation it is necessary to apply the formula for the area of a circle. This way we know the cross-sectional area of the conductor.
Where:
- r - radius of the circle,
- D - circle diameter,
- π = 3,14.
As an example, let us calculate the wire parameter of interest to us using the already known data from the above calculations. So, our diameter is 0.68 mm. Therefore, it is still necessary to find the radius. It turns out 0.68 / 2 = 0.34 mm. Now we substitute the obtained results into the formula:
S = π * R² = 3.14 * 0.34² = 0.36² mm
The same can be done for the second part of the equation. The value will be similar:
Now you can always define cable cross-sectionknowing the diameter. In this case, you can use any of the above two formulas - which one you like, use that one.
Diameter table and their cross-sectional area
Knowing the formulas and being able, thanks to them, to calculate the necessary data at any time is great. But there is also an easier way to find out the cross section, without resorting to not always convenient calculations. For this, there is a table of correspondence of diameters to area. It contains the most common data, thanks to which it is easy to determine the section, knowing the diameter. You just need to print this table on a small piece of paper and carry it in your pocket or purse.
Using this table is extremely simple. Almost all cables have their own markings, which are indicated directly on the insulation and / or on the tag. It often happens that the actual cable cross-section does not coincide with that shown on the marking. The table can be an indispensable assistant in such cases. To do this, you just need to look at the marking (for example, AVVG 3x2.5). The value following the "x" sign is the declared section, in our case it is 2.5 mm. The first number means that the cable has 3 wires, but in our situation it does not matter.
It is also easy to calculate and cable diameter by section, the table can help us perfectly with this, but this must be done in the reverse order.
To check the correctness of the statement that the cross-section of this cable is 2.5 mm, we need to measure its diameter in any of the above ways. So, if in a specific case the diameter is 1.78 mm or a value close to it (the errors are still allowed), then everything is correct, we were not deceived and the wire really satisfies the declared requirements. We can see this from the table, finding a value of 1.78 (diameter), which corresponds to an indicator of 2.5 mm.
In addition, it will be useful to carefully check the insulation. It must be even, uniform, free from damage and other defects. In pursuit of profit, manufacturers of cheap products go to any tricksto somehow save on material. Therefore, cheapness may not always be profitable.
Often, cables do not use a solid wire, but a stranded one - consisting of many small wires twisted together. It may seem that measuring the cross section of such cables is impossible or too difficult. But this is a deep misconception. Finding out the data of a multicore cable we are interested in is extremely simple. This is done similarly to the previous method using a single-piece wire, i.e. first we measure the diameter, and then we calculate or find out the data of interest to us from the table.
But this must be done correctly. You can't just take and measure the total diameter of the entire structure. There is always a certain distance between individual "hairs", so if measurements are taken along the total diameter, then at the output we can get completely wrong data.
In order to find out the required value of a stranded cable, we need to calculate the total cross-section of the wires. You just need to take a separate wire and measure its diameter. Next, we count the number of all such wires in the wire and multiply by the diameter of one of them. As a result, we will get the total diameter of the entire wire. Knowing these parameters, it is already easy to find out the section.
