A single formula for calculating the cable cross-section by diameter is used for all cases. It looks like this:
D – core diameter.
The diameter of the core is usually indicated on the braid of the wire or on a general label with other technical characteristics. If necessary, this value can be determined in two ways: using a caliper and manually.
The first method of measuring the diameter of the ig data is very simple. To do this, it is necessary to clean it from the insulating shell, and then use a caliper. The value it shows is the diameter of the core.
If the wire is multi-core, it is necessary to disassemble the bundle, recount the advertising raises the product’s position and measure only one of them with a caliper. There is no point in determining the diameter of the entire bundle – such a result will be incorrect due to the presence of voids. In this case, the formula for calculating the cross-section will look like this:
D – core diameter;
a – number of wires in the core.
If you don’t have a caliper, you can determine the diameter of the wire manually. To do this, you need to free a small section of it from the insulating sheath and wind it onto a thin italy numbers object, such as a pencil. The turns should fit tightly together. In this case, the formula for calculating the diameter of the wire’s core looks like this:
L – length of wire winding;
N – number of full turns.
The longer the winding length of the core, the more accurate the result will be.
Select by table
Knowing the diameter of the wire, you can determine its cross-section using a ready-made dependence table. The table for calculating the cable cross-section by the core diameter looks like this:
When the cross-section is known, it is possible to determine the values of permissible power and current for copper or aluminum wire. In this way, it will be possible to find out what load parameters the conductive core is designed for. For this, a table of the dependence of the cross-section on the maximum current and power will be needed.
Converting watts to kilowatts
To correctly use the table of wire cross-section dependence on power, it is important to correctly convert watts to kilowatts.
1 kilowatt = 1000 watts. Accordingly, to get the value in kilowatts, the power in watts must be divided by 1000. For example, 4300 W = 4.3 kW.
Examples
Example 1. It is necessary to determine the values of permissible current and power for a copper wire with a core diameter of 2.3 mm. Supply voltage is 220 V.
First of all, you need to determine the cross-sectional area of the core. This can be done using a table or a formula. In the first case, the value is 4 mm2, in the second – 4.15 mm2.
The calculated value is always more accurate than the tabulated value.
Using the table of cable cross-section dependence on power and current, we can find out that for a copper core cross-section of 4.15 mm2, a power of 7.7 kW and a current of 35 A are permissible.
Example 2. It is necessary to calculate the current and power values for an aluminum multi-core wire. The core diameter is 0.2 mm, the number of wires is 36, the voltage is 220 V.
In the case of a multi-core wire, it is not practical to use tabular values; it is better to use the formula for calculating the cross-sectional area:
Now we can determine the power and current values for a 2.26 mm2 multi-core aluminum wire. Power – 4.1 kW, current – 19 A.
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 it does not correspond, 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 place of work.
Why does the discrepancy arise?
Despite the fact that in the conditions of modern competition, manufacturers are trying their best not to lose their customers, some of them resort to cheating. To do this, they save metal by reducing the diameter. It is enough to remove just a couple of square millimeters, and on hundreds of kilometers of cable this will pay off with a significant reduction in cost.
And then they will lower the price for the buyer, and they themselves will be satisfied. But the consumer, in the end, puts himself at risk because the resistance of the conductor is much lower than stated. And in the place where such a wire is laid, there is a risk of fire.
Methods for determining the cross-section of a wire step by step
There are several ways to measure the cross-section by the diameter of the core. If the wire is single-core, then the measurements will be taken directly on it, but one conductor must be untangled from the cable coil. After that, it is cleaned of insulation so that only metal remains.
Fig. 1: Removing insulation from wire
To calculate the area of a circle using the radius, use the formula: S = π × R2, where:
- π is a constant equal to 3.14;
- R is the 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.
Fig. 2: Wire diameter
Depending on the methods of measuring the diameter, the following methods of calculating the cross-section are distinguished.
