# Grounding and equipotential lines

In my textbook it says:

One of the rules for static electric fields and conductors is that the electric field must be perpendicular to the surface of any conductor. This implies that a conductor is an equipotential surface in static situations. There can be no voltage difference across the surface of a conductor, or charges will flow. One of the uses of this fact is that a conductor can be fixed at zero volts by connecting it to the earth with a good conductor—a process called grounding. Grounding can be a useful safety tool. For example, grounding the metal case of an electrical appliance ensures that it is at zero volts relative to the earth.

I understand that there is no movement of charge in conductors in electrostatic conditions, and hence there must be no voltage across the conductor is 0. However, how would connecting it to ground fix it as 0 volts. Is it because if any extra charge enters the conductor it will immediately will go the earth? Secondly, why does it have the connection to the earth have to be with an equipotential surface?

why does it have the connection to the earth have to be with an equipotential surface?

It does not. A conductor in an electrostatic scenario is an equipotential surface regardless of whether it is connected to ground or not.

However, how would connecting it to ground fix it as 0 volts.

The first thing to understand is that what you call 0 V is simply a matter of convention. You are free to choose any location as your reference location and say that is 0 V. Only differences in voltage have physical meaning. So by convention 0 V refers to the ground/earth voltage, but it is just a convention.

The second thing to understand is why connecting a device to the earth is safety relevant. Humans, lacking wings, spend most of their time in contact with the ground. Therefore, if a human touches a piece of metal which is not at the same potential as the earth there is a high risk that the human may become a conductor between the two different voltages and thus be shocked. However, if the conductor is at the same voltage as the earth then a human touching both the earth and the conductor will not be shocked. This is the purpose of grounding appliances to earth.

So in summary a grounded conductor forms an equipotential surface with the earth, and this reduces the risk of electric shock.

• Could you elaborate more on the relationship between equipotential surfaces and grounding. Commented Nov 30, 2018 at 23:35