Ground

The term ground or earth usually means a common return path in electrical circuits. The terms earth return and ground return are also common. 

Grounding is primarily used for safety to prevent electric shock or fires caused by a voltage potential between the earth and a conductor such as an appliance cabinet or chassis. A power ground serves to provide a return path for fault currents and therefore allow the fuse or breaker to disconnect the circuit. Power and signal grounds often get connected together, usually through the metal case of the equipment.

Grounding is often used to conduct lightning strikes harmlessly to earth rather than starting fires and damaging equipment. It is also used to control electrical noise in computer, audio and video, and communications circuits. This illustrates that an electrical ground should have an appropriate current-carrying capability in order to serve as an adequate zero-voltage reference level.

In a mains (AC power) wiring installation, the ground is a wire with an electrical connection to earth, that provides an alternative path to the ground for heavy currents that might otherwise flow through a victim of electric shock. This power ground grounding wire is (directly or indirectly) connected to one or more earth electrodes. These may be located locally (can be as simple as a metal rod or stake driven into the earth, or a connection to buried metal water piping), be far away in the suppliers network or in many cases both. This grounding wire is usually but not always connected to the neutral wire at some point and they may even share a cable for part of the system under some conditions. The ground wire is also usually bonded to pipework to keep it at the same potential as the electrical ground during a fault. 

     Ground symbols

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