Why Earth Conducts and How Grounding Works

Hello dear subscribers and guests of my channel. Today I want to talk with you about why the earth conducts an electric current, and most importantly why grounding works.

What is grounding and how does it work

So, you all know perfectly well that grounding is the deliberate connection of the metal cases of electrical appliances or any point in the network with a grounding device. At the same time, in electrical engineering, due to grounding, they provide protection against the dangerous action of electric current by reducing the touch voltage to completely safe levels for humans.

But a logical question arises: "So why is the earth such a good conductor?" Let's figure it out.

How the earth conducts current

Of course, the earth itself is not an insulating material, because it contains various liquids and salt solutions that are quite capable of conducting an electric current.

But such a conductor is far from ideal, but it still works great, and here's why.

An infinitely large section equals zero resistance

Let's look at the following table:

And now let's remember this formula for calculating resistance:

So, in fact, we absolutely do not care what the length and resistivity are. After all, the cross-sectional area of ​​the earth is so large that the resistance can be considered equal to zero.

To understand, let's make a comparative analysis, and take silver and a material such as graphite from the table above.

As you already understood from the table, silver conducts electricity much better (due to lower resistivity) than graphite. But if we increase the cross-sectional area of ​​graphite a million times, then the resistance of graphite will be significantly lower than that of silver. The exact same effect works in the case of the ground.

It seems that the zero ground resistance has been sorted out, and it would seem that everything is just fine, but there is one very important point. In order for the dangerous potential to go away precisely through the grounding, and not become the cause of electric shock to a person, it must meet a number of requirements.

Features of the grounding device

So, in order for the grounding to work as it should, it must have a minimum transfer resistance, and this, in turn, is achieved due to the following factors:

1. A large contact area must be provided at the points of the circuit connection. That is, the weld seam on the plates must be at least 10 cm.
2. The entire system of electrodes must be buried below the soil freezing line.
3. The total resistance of the ground loop should not exceed 4 ohms. If this condition is not met during measurements with special devices, then it is necessary to increase the ground loop until the required parameters are achieved.

This is how grounding performs its protective function due to the fact that the earth has an infinitely large cross section. And since the current flows only along the path of least resistance, even in the event of a breakdown of insulation at an electrical appliance, whose body is grounded, nothing terrible will happen, since the dangerous potential will go through the ground loop into the ground.

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