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  • How to calculate the resistance of the wire: detailed instructions

    1. Answer to the reader
    2. Theory and practice
    3. Calculate the resistance

    Good day! I'm going to connect an electric hob and oven at my own home. Due to the fact that I had heard that standard wiring could not withstand such pressure and would become overheated, I decided from the panel to throw individual wires through an additional machine.

    I already have an automatic machine, but I don’t know how to choose the wire section. Tell me how to calculate the resistance of the wires for my needs - you will have to throw about 20 meters of wires, no less.

    Tell me how to calculate the resistance of the wires for my needs - you will have to throw about 20 meters of wires, no less

    The name of this person was called the unit of resistance of electricity

    Answer to the reader

    Welcome, unfortunately not introduced reader! We will naturally help you with the calculations, but nevertheless we recommend bringing a specialist to the problem, because you need to choose the right machine, not just the conductor. However, if you know for sure that the parameters of the machine will do, then you have nothing left ...

    Theory and practice

    So, if a person is even slightly familiar with the basics of electrical engineering, he should know that the thicker the wire, the less resistance.

    • It is theoretically possible to compare this with a water pipe running water. If the diameter of the pipe is sufficient, then the liquid flows through it without experiencing any hydraulic resistance, and vice versa, a small opening increases the pressure in the pipe, the throughput drops, and the hydraulic resistance increases.
    • Also, the flow of electrons can be represented in the form of water that attempts to leak inside the wire. However, electricity is a completely different nature, respectively, and its physical properties are different.
    • What can lead too high resistance? The most trivial is a voltage drop, as a result of which some incandescent lamp will become dimmer, and some electrical appliance will not be able to start.
    • A direct consequence of the passage of a powerful current through a conductor with a sufficiently high resistance will be its overheating.

    From the author! Once we connected a welding machine, well, to a very bad extension cord, and after a few minutes of work, the wire literally caught fire. The benefit of a short circuit did not happen, but it was very likely. As is clear, in a residential area such situations are unacceptable.

    We recommend to act in the following sequence:

    • First of all, find out exactly what load both of your devices create in the conditions of operation at maximum power. We are interested in the current, measured in amperes, or power - Watts.
    • You will easily find these parameters in product passports.
    • If both devices are powered from the same line, then add the resulting values.
    • Next, resort to using a table that will accurately determine the cross section of the wire.

    In the photo - the table of selection of the conductor

    • As can be seen from the table above, the maximum current for a copper wire with an area of ​​0.5 should not exceed 11 Amps.

    Tip! In residential areas today is not allowed to use aluminum wires. Apply only copper.

    • In principle, this data could be limited to, throwing some stock, however, such tables do not show what should be the maximum resistance of the wire, that is, the length of the conductor is not taken into account. Therefore, for greater accuracy can not do without calculation.

    Calculate the resistance

    All data can be obtained from the tables

    So, we remember - the wire is thicker, the resistance is less. Next will be an instruction on how to calculate everything exactly.

    • To do this, we need to know the resistivity of the conductor material. In conventional networks, you are unlikely to find the silver wires, so take the standard copper as a basis. It is 0.017.
    • The very same wire resistance is calculated by the following formula:; where R is the resistance, p is the resistivity of the conductor, l is the length of the wire and s is the area of ​​its cross section.
    • Suppose that your stoves together will be able to load the network at 16 amps, which means that we can take a wire of 0.75 mm2. We remember that you need at least 20 meters. So, we consider: 0.017 * 20 / 0.75 = 0.45 Ohm
    • You can use the table, but the result will not be as accurate. We see that 100 meters of copper wire of the section we need has 2.38 ohms of resistance. We divide this value by five (up to 20 meters) and we get 0.476 Ohm - the difference is at the level of error, but still.
    • Due to the fact that electricity goes through two veins, we multiply the resulting value by 2 and we get 0.9 Ohms.
    • Now you can calculate the voltage loss by the formula: dU = R * I = 0.9 * 16 = 14.4 Volts.
    • We translate the resulting voltage into a percentage: 14.4V / 220V * 100 = 6.54%

    According to existing regulations, 5% voltage loss is allowed. As you can see, in our case, the value turned out more, which means that the resistance of the conductor is too large, so we increase the cross section of the wire and repeat the calculations.

    So, we found the resistance of the wire, and as you can see, it’s not so difficult to do it with our own hands and head. Additionally, the attached video will help to understand the material. Be wise to the matter, because the price of the issue is the security of you and your home.

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