What Is Earth & Why & How Do We Connect To It?

In the field of electricity, the thin layer of material that covers our planet, whether it be made of rock, clay, chalk, or another material, is referred to as earth. What need then do we have to link anything to it? After all, the earth isn’t exactly a good conductor.

At this point, it might be wise to look into potential differences (PD). The definition of a PD is accurate: a difference in potential (volts). In this manner, two conductors with, let’s say, PDs of 20 and 26 V have a PD between them of 26 – 20 = 6 V. The original PDs (i.e., 20 and 26 V) are the PDs between 20 V and 0 V and 26 V and 0 V. So where does this 0 V or zero potential come from? In our situation, the earth is the obvious answer. The definition of the earth is, therefore, the conductive mass of earth, whose electric potential at any given point is typically assumed to be zero.

So, if we connect a voltmeter between a live part (such as the line conductor of an outlet socket) and the earth, the voltmeter may read 230 V because the conductor is at 230 V and the earth is at zero. To complete the circuit, one can use the earth as a path. If we connected our voltmeter between, say, the positive 12 V terminal of a car battery and the earth, we would measure nothing at all because in this situation the earth is not a component of any circuit.

Therefore, a person in an installation touching a live part while standing on the ground would substitute for the voltmeter and risk receiving a powerful electric shock. Keep in mind that only 50 mA, or 1/20 A, of shock current, is considered to be lethal for humans. The same thing would happen if they touched a broken appliance and a gas or water pipe.

Figure1.1: (a)Earth path (b)No earth path

As we have seen, connecting all metallic components to earth and joining (bonding) them together is one way to offer some degree of protection against these effects. This guarantees that every piece of metalwork in a healthy installation is at or close to 0 V and that, in the event of a fault, every piece of metalwork will rise to a similar potential. As a result, there wouldn’t be much PD between two of these metal parts when they come into contact with each other, preventing a potentially harmful shock.

Figure 1.2: Shock path

Unfortunately, unless it is extremely wet, the earth itself is not a good conductor. As a result, it offers a significant obstruction to the flow of fault current. Usually, this resistance is sufficient to keep the fault current at a level well below the protective device’s rating while still allowing the circuit to function improperly. This is obviously a bad situation.

Consumers can connect to a metallic earth return conductor in all but the most remote areas. This conductor is ultimately connected to the supply’s earthed neutral. It goes without saying that this provides a low-resistance path for fault currents to operate the protection.

In conclusion, bonding between metallic parts places such parts at a similar potential even under fault conditions, and connecting metalwork to the earth place that metal at or near zero potential. We have significantly decreased the risk of electric shock by adding a low-resistance earth fault return path, which will enable the circuit protection to operate very quickly.

Note: If you don’t know about electrical work then don’t do this work at home. You need a qualified electrician. Read About our electrician.

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