In electrical engineering, ground pork or earth is a reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth. Electrical circuits may be connected to ground for several reasons. Exposed conductive parts of electrical equipment are connected to ground, to protect users from electrical shock hazard.

If internal insulation fails, dangerous voltages may appear on the exposed conductive parts. Connection to ground also limits the build-up of static electricity when handling flammable products or electrostatic-sensitive devices. An electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. Long-distance electromagnetic telegraph systems from 1820 onwards used two or more wires to carry the signal and return currents. In the late nineteenth century, when telephony began to replace telegraphy, it was found that the currents in the earth induced by power systems, electric railways, other telephone and telegraph circuits, and natural sources including lightning caused unacceptable interference to the audio signals, and the two-wire or ‘metallic circuit’ system was reintroduced around 1883. Electrical power distribution systems are often connected to earth ground to limit the voltage that can appear on distribution circuits. A distribution system insulated from earth ground may attain a high potential due to transient voltages caused by static electricity or accidental contact with higher potential circuits.

An earth ground connection of the system dissipates such potentials and limits the rise in voltage of the grounded system. This is called “system grounding” and most electrical systems are required to be grounded. NEC and the UK’s BS 7671 list systems that are required to be grounded. Permanently installed electrical equipment, unless not required to, has permanently connected grounding conductors.