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Definition

ground

A ground is a direct electrical connection to the earth, a connection to a particular point in an electrical or electronic circuit, or an indirect connection that operates as the result of capacitance between wireless equipment and the earth or a large mass of conductive material.

Electrical grounding is important because it provides a reference voltage level (called zero potential or ground potential) against which all other voltages in a system are established and measured. An effective electrical ground connection also minimizes the susceptibility of equipment to interference, reduces the risk of equipment damage due to lightning, eliminates electrostatic buildup that can damage system components, and helps protect personnel who service and repair electrical, electronic, and computer systems. In effect, an electrical ground drains away any unwanted buildup of electrical charge. When a point is connected to a good ground, that point tends to stay at a constant voltage, regardless of what happens elsewhere in the circuit or system. The earth, which forms the ultimate ground, has the ability to absorb or dissipate an unlimited amount of electrical charge.

An earth ground usually consists of a ground rod (or a set of ground rods) driven into the soil. At sea, the salt water forms a good earth ground if a corrosion-resistant metal plate having large surface area (such as the hull or keel) is placed in contact with it. In a car, a truck, a boat in fresh water, an aircraft, or a spacecraft, there is no such thing as a true earth ground. But if the mass of metal comprising the vehicle is substantial, that mass can simulate an earth ground reasonably well. An earth ground minimizes the susceptibility of electronic equipment to interference from other devices. In large, base-station wireless installations, a good earth ground also provides a certain measure of protection from the destructive effects of lightning.

A chassis ground is a connection to the main chassis of a piece of electronic or electrical equipment. In older appliances and in desktop computers, this is a metal plate, usually copper or aluminum. In some modern equipment, it is a foil run on the main printed circuit board, usually running around the periphery. Chassis ground is sometimes called common ground. It provides a point that can be considered to have zero voltage. All other circuit voltages (positive or negative) are measured or defined with respect to it. Ideally, all chassis grounds should lead to earth grounds.

In wireless systems, a radio-frequency ( RF ) ground can be obtained by capacitive coupling between devices and the earth. In some cases, several wires known as radials, parallel to and near the earth's surface, are necessary to obtain a good RF ground. At higher frequencies, radials are not always necessary. The capacitance between a handheld radio transceiver or cell phone set and the user's body, and the capacitance between the user's body and the earth, can provide a reasonably good RF ground. Certain types of antenna s can function effectively without an RF ground.

This was last updated in March 2010

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