How to find out the wire cross section in various ways
Often found in the supermarket electrical products without tags and identification marks. Among it can easily be a coil of wire or cable. How do you know if the wire size is right for your particular situation? The answer is simple - measure it or consult the seller.
Anyone who sells cables and wires can tell you what kind of load they can withstand. In addition, inscriptions (numbers) are punched on the wires, characterizing the cross section and the number of cores. But in real practice, not everything is as simple as it seems. The quality of manufactured cable products has noticeably deteriorated in recent years.
Problems of quality of produced wires
Many manufacturers of cable and wire products, trying to earn more, artificially underestimate the thickness of the insulation and overestimate the diameter of the cable. By specifying a larger wire cross-section than in reality, the manufacturer saves a very large amount. For example, the production of a thousand meters of copper wire with a cross section of 2.5 mm2 requires 22.3 kg of copper, and in the manufacture of a wire of 2.1 mm2, only 18.8 kg are required. So it turns out a saving of 3.5 kg of copper.
Another way to reduce the cost of products is the manufacture of a conductive core from low-quality raw materials. When cheap impurities are added, the conductance decreases, therefore, cable length calculations must be changed.
Why do you need to calculate the cable load?
This question often arises when laying wiring in an apartment or your house. First, all planned loads are considered, and then the required wire cross section is determined. Then the necessary material is purchased in the store and the electrical wiring is installed in the house.
As a result of the operation of the new wiring, the machine on the electrical panel first “knocks out”, and then damage to the wire is detected. Moreover, it often turns out to be completely melted, as a result of which a short circuit occurred. It turns out that incorrect calculations were made, and how to find out the minimum allowable value of the wire cross section in this case?
To avoid serious overloads, it is necessary to calculate how many electrical appliances in the apartment will be used at the same time. Among the most powerful household appliances that are commonly used at home for cooking and creating our comfort, we can distinguish:
- electric stove;
- air conditioner;
- microwave;
- electric kettle;
- iron;
- washing machine and dishwasher;
- coffee grinder;
- vacuum cleaner.
The power consumption of this household appliances ranges from 1 to 2 kilowatts (with the exception of the electric stove).
Important! If the cross section of the wire is indicated incorrectly (underestimated), then when using it, the occurrence of large overloads is natural, which leads to a fire in the wiring.
How to calculate?
Experienced electricians can "by eye" with great accuracy determine the cross section of the wire. It is much more difficult for an ordinary person to do this. Therefore, it is best to calculate the cable cross-section by diameter right in the store. At the very least, it will come out much cheaper than eliminating the consequences of a short circuit due to an overload in the power grid.
Let's try to do this on specific examples using the arithmetic formulas of school mathematics.
Everyone roughly understands what the cross section of the wire is. If you bite it across with wire cutters, you can see a round cross-section of a copper or aluminum core. It is measured according to the 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 more current can pass in 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 Skr = 0.785d2, it can be seen that in order to calculate the cross-sectional area, you need to know the exact diameter of the wire. To do this, it is necessary to clean the core from insulation.
Stranded wire calculation
Stranded wire (stranded) is a single-core wire twisted together. Anyone who is at least a little friendly with mathematics understands perfectly well that it is necessary to count the number of these wires in a stranded wire. After that, the cross section of one thin wire is measured and multiplied by their total number. Consider the following options.
Calculation with a caliper
The measurement is carried out with a vernier caliper with a conventional scale (or micrometer). Experienced craftsmen always have this tool at hand, but not everyone is professionally engaged in electrics.
To do this, using the example of a VVGng cable, cut a thick sheath with a knife and spread the cores in different directions.
Then choose one core and clean it with a knife or scissors. Next, measure this core. Should be 1.8mm. Refer to the calculations as proof of correct measurement.
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 handy, you can use the methods at hand, using a pencil and a 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, it turned out 10 turns with a total winding length of 18 mm. It is easy to calculate the diameter of one turn, for this we divide the total length by the number of turns.
As a result of all the calculations made according to the formula, get the desired core diameter. 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 are the same.
Using tables
How can you find out and measure the cable cross-section if there was no caliper, no ruler, no micrometer at hand. Instead of racking your brains over complex mathematical formulas, it is enough to remember that there are already ready-made tables of values \u200b\u200bfor measuring the cable cross section. There are, of course, very complex tables with many parameters, but, in principle, it is enough to start with the simplest of the two columns. In the first column, the diameter of the conductor is entered, and in the second column, the finished values \u200b\u200bof the wire section are given.
Conducting section table for enclosed wiring There is another "approximate" method that does not require measuring the thickness of individual wires. You can simply measure the cross section (diameter) of the entire thick scroll. This method is usually used by experienced electricians. They can find out the cable cross-section both “by eye” and with the help of tools.
