### 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.