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Equipotential bonding involves electrically connecting metalwork so that it is at the same voltage everywhere. Exact rules for electrical installations vary by country, locality, or supplying power company. [2] Equipotential bonding is done from where the distribution wiring enters the building to incoming water and gas services.
The primary reason for the use of isolated grounds (IG) is to provide a noise-free ground return, separate from the equipment grounding (EG) return. The EG circuit includes all of the metal conduit, outlet boxes, and metal enclosures that contain the wiring and must be grounded to provide a safe return path in case of fault currents.
"T" — Earth connection is by a local direct connection to earth (Latin: terra), usually via a ground rod. "N" — the earth connection is supplied by the electricity supply network, either separately to the neutral conductor (TN-S), combined with the neutral conductor (TN-C), or both (TN-C-S). These are discussed below.
The amount of cross bonding, and the topology of the grids, is determined by the expected frequencies in the signals to be carried and the uses the installation will be put to. A ground grid is provided primarily for safety, and the size of the conductors is probably governed by local building or electrical code. One factor to keep in mind is ...
In special circumstances (not domestic installations) bonding with deliberate lack of connection to Earth (earth-free local equipotential bonding) may be used. Bonding, by the IEC 60364 terminology used in BS 7671, should not be seen as just an extra to earthing.
In an electrical substation a ground (earth) mat is a mesh of conductive material installed at places where a person would stand to operate a switch or other apparatus; it is bonded to the local supporting metal structure and to the handle of the switchgear, so that the operator will not be exposed to a high differential voltage due to a fault ...
Normal circuit currents flow only in the neutral, and the protective earth conductor bonds all equipment cases to earth to intercept any leakage current due to insulation failure. The neutral conductor is connected to earth at the building point of supply, but no common path to ground exists for circuit current and the protective conductor.
Faraday cage demonstration on volunteers in the Palais de la Découverte in Paris EMI shielding around an MRI machine room Faraday shield at a power plant in Heimbach, Germany. A Faraday cage or Faraday shield is an enclosure used to block some electromagnetic fields.