Ground (electricity)

In electrical engineering, ground or earth may refer to reference ground – a reference point in an electrical circuit from which voltages are measured, earth ground – an electrically neutral node that has a lot of available charges (e.g. the physical ground of Earth), or common ground – a common return path for electric current (also called neutral in electric power systems). Ground current or earth current is the current that flows through a reference ground, earth ground, or common ground. To ground or to earth an object is to electrically connect the object to a reference ground, earth ground, or common ground. Electrical circuits may be grounded for several reasons.

A protective earth conductor (PE conductor) is a conductor that connects an electrical equipment from its exposed and conductive but normally unenergized part to common ground. If the conductor is a wire, it is also called ground wire or earth wire. Ground wire is often used for lower voltage systems and is often colored green, or green and yellow, per standard. The conductor is used to protect users from electrical shock hazards. If internal insulation fails and the equipment is turned on, dangerous voltages may appear on the exposed conductive parts and accidentally energized the parts. This results in a fault. Connection of exposed conductive parts to a PE conductor provides a low-impedance path for current to flow back to the incoming neutral and allows circuit breakers (or RCDs) to interrupt power supply. The current that flows through the low-impedance path is high and will usually trip the breaker or melt the safety fuse if any. Even if the circuit does not break due to failures, the current still only flows mainly through the PE conductor instead of the user upon touching the exposed conductive part. A PE conductor is an essential part of the safety provided by the earthing system. A safety ground is a loose term that refers to a common ground that is used for safety purposes.

Connection to earth ground limits the build-up of static electricity. This connection is crucial for safety when handling flammable products or electrostatic-sensitive devices. In a large-scale electrical system, a piece of conducting material, called grounding electrode or earthing electrode, is buried in the soil to act as an earth ground. A grounding electrode conductor or ground conductor is a conductor that connects an electrical equipment to the grounding electrode. In some telegraph and power transmission circuits, the physical ground (an earth ground) itself can be used as one conductor of the circuit, saving the cost of installing a separate return conductor (see single-wire earth return and earth-return telegraph). In an electric power system, the neutral is connected to earth ground, close to the point of entry.

For measurement purposes, the ground of the Earth, having a reasonably constant potential, serves as a reference ground against which other potentials can be measured. An electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. Circuits in portable electronic devices, such as cell phones and media players, as well as circuits in vehicles, have a reference ground (also called chassis ground in those cases).

In electronic circuit theory, a signal ground is the common ground and reference ground for electric signal; and a power ground is the common ground for power current. The signal ground and power ground may be connected. There is usually a large conductor attached to one side of the power supply (such as the "ground plane" on a printed circuit board), which serves as the common ground, the common return path for current from many different components in the circuit. The signal ground and power ground are usually assumed to be an earth ground and idealized as an infinite source or sink for charge, which can absorb an unlimited amount of current without changing its potential. Where a physical ground connection has a significant resistance, the approximation of zero potential is no longer valid (no longer a valid reference ground). Stray voltages or earth potential rise effects will occur, which may create noise in signals or produce an electric shock hazard if large enough.