Importance of Earth Ground

Voltage can not be defined at a single point it is by definition the difference in potential between two points.

 However, many schematics  makes use of the conversion of taking the earth as defining zero volts, so that all other voltages are implicitly referenced to this potential.

The concept is often referred to as earth ground, and is fundamentally tied to safety regulations designed to prevent fires, fatal electrical shocks, and related mayhem. The symbol for earth ground is shown in the figure below

Since earth ground is defined as zero volts, it is often convenient to use this as a common terminal in schematics. The circuit of Fig a is shown redrawn in this fashion in Fig b. Where the earth ground symbol represents a common node. It is important to note that the two circuits are equivalent in terms of our value for Va.

Example

The fact that the common terminal of a circuit may or may not be connected by some low-resistance

pathway to earth ground can lead to potentially dangerous situations. Consider the diagram of Fig, which depicts an innocent bystander about to touch a piece of equipment powered by an ac outlet.

Only two terminals have been used from the wall socket; the round ground pin of the receptacles

was left unconnected. The common terminal of every circuit in the equipment has been tied together

and electrically connected to the conducting equipment chassis;

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