Ground (electricity)

The term ground (or earth) usually means a common return in circuits.

Table of contents

1 Meanings
2 Uses
3 History
4 See also
5 Source

Meanings

In electrical engineering, the term ground or earth has the following meanings:

An electrical connection to earth via an earth-electrode which can be as simple as a metallic ground rod or stake driven into the earth, a connection to buried metal water piping, or an extensive system of buried rods and wires. The resistance of the electrode-to-earth connection determines its quality, and is improved by increasing the surface area of the electrode in contact with the earth, increasing the depth to which it is driven, using several connected ground rods, increasing the moisture of the soil, improving the conductive mineral content of the soil, and increasing the land area covered by the ground system.
In an electrical circuit, a common return path that usually (a) is connected to an earth-electrode subsystem and (b) is extended throughout a facility via a facility ground system consisting of the signal reference subsystem, the fault protection subsystem, and the lightning protection subsystem.
In an electrical circuit, a common return path that (a) may not necessarily be connected to earth and (b) is the zero voltage reference level for the equipment or system. This is often referred to as a floating ground.

Uses

Grounding is primarily used for safety to prevent electric shock or fires started from a voltage potential existing between the earth and a conductor such as an appliance cabinet or chassis. 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.

History

Historically, in the 1800s, the literal use of the earth as the return path limited the effectiveness of the telegraph; after the use of multiple wires, one for ground, the telegraph became more usable than its single-wire implementation. This illustrates that an electrical ground should also have appropriate current-carrying capability in order to serve as an adequate zero voltage reference level. In the 1900s, it has, though, been proven that the literal use of the earth as a effective return path is possible.

Early telegraph and telephone systems utilized an earth ground as the return path of the circuit, allowing communications pole lines to be built with only one conductor wire such as the transcontinental telegraph line constructed in 1861 by the Western Union Company between St. Joseph, Missouri, and Sacramento, California. During dry weather, the ground connection often developed a high resistance which required pouring water on the ground rod to enable the telegraph to work or phones to ring. Since the earth also carries currents induced by power systems, electrical railways, and natural sources including lightning, replacing the ground return with a second wire -- thus creating a transmission line not using the earth -- greatly improved the reliability of telegraph and telephone circuits. There is a tradeoff between the cost of the wire and the reliability of the connection.

Source

Federal Standard 1037C in support of MIL-STD-188''