A very important parameter when laying electrical networks is saving. By increasing the wire cross-section from 1.5 mm2 to 2.5 mm2, you can get such a serious difference in the amount that the customer simply will not "stretch" the budget. But by choosing a wiring of a small cross-section, the master runs the risk of facing such a serious problem as a voltage drop. What is it and how to prevent this from happening - further in the article.
Starting from the basics: Ohm's law in action
Before dealing with the concept of voltage drop, it is necessary to recall the fundamental and fundamental law in electrical engineering, namely, Ohm's law for a separate section of the circuit:
I = U / R
Where the current (I) is directly proportional to the voltage (U) and inversely proportional to the resistance (R). Why exactly for a separate section of the chain? Because Ohm's law for a complete section of a circuit includes the sum of active and reactive (inductive and capacitive) resistances. Such numerous data are needed for serious calculations, most often already in the field of energy.
From this formula, you can find the voltage - the potential difference:
U = I * R
Such a simple equality accompanies all electricians in their work and is useful when calculating the voltage drop in a cable of a certain length.
Calculation of wiring for voltage drop
Does the length and size of the cable affect the voltage? It affects and this is perfectly visible on the example of Ohm's law, which was considered in detail in the previous paragraph.
Each conductor has some kind of resistance, the value of which depends on the material of the conductor itself. For example, copper conducts electric current much better than aluminum, and silver better than copper, etc. Cable, all over its length creates a slight resistance to current, which ultimately leads to a voltage drop across its ends.
In order to find the voltage drop across cables, you need to find its resistance by the formula:
r = ρ * (l / S)
Where ρ (Greek letter "ro") is the specific resistance of the material from which the conductor is made. It must be found in the tables of electrical reference books. l is the length of the conductor, and S is its cross-section.
When the resistance of a wire or cable is found, you can calculate the voltage drop across its section according to Ohm's law. To strengthen the information, you can use the following example:
The lamp power is 100 W.
The conductor is copper, 5 m long and 1.5 mm2 in cross section.
The voltage drop will be:
U = 0.45 A * 3.35 Ohm = 1.5 V.
With a consumer power of 100 V, the voltage drop across a 5 m cable with a cross section of 1.5 mm2 will be 1.5 V.
Why should the wires be larger at low voltage?
To answer this question, you need to refer to the example from the previous paragraph. On a conductor 5 m long and with a cross-section of 1.5 mm2, the voltage drop was 1.5 V, which is quite small, for example, for a 220 V home network and is practically not noticed on 380 V lines. And if there is such a drop in the on-board network of a passenger car, where the potential difference does not exceed 12 V? Quite tangible. That is why, in order to compensate for the voltage drop, wires of a larger cross section are mounted.