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Electrical bonding is an electrical safety measure intended to prevent accidental electrical shock. Buildings, whether residential, commercial, or industrial, all have various metal works as part of normal construction. Water pipes, metal beams, and other normally non-current-carrying metal components within a structure can conduct electricity at differing rates in the event of contact with exposed electrical wiring. By attaching these metal components together through a copper wire network connected to an earthing system, each component will carry the same level of current if accidentally electrified.
Most countries require an earthing system of some form for all structures, including homes, commercial facilities, and industrial complexes. Aircraft, boats, and even structures in outer space require a similar grounding system, although such applications require an isolated system rather than grounding to the earth. Earthing systems provide a pathway for erroneous high voltage to flow and be absorbed into the ground, with earth having the ability to absorb an unlimited amount of electricity. Lightning rods on residential structures are one example of an earthing system.
Should a short circuit, electrical surge, or other wayward electrical event occur, grounding an electrical system to the earth provides a safe venue to pour out the overflow voltage. While an earthing system can conduct an unlimited amount of electricity into the ground, it does not protect from differing potentials above ground in components not connected to the system. For example, steel beams not connected to an earthing system may conduct electricity at a different rate than copper piping. Accidentally touching an electrified copper pipe while simultaneously touching a steel beam can result in severe injury due to differing electrical potentials and no ground. As such, electrical bonding is needed, whereby each metal component is connected by a copper ground wire that is then connected to an earthing system, creating a completed circuit.
To illustrate the purpose of electrical bonding, consider a residential structure. Wiring for various outlets, appliances, heating and cooling systems, and other necessities often intersects with plumbing, metal duct work, and other non-current-carrying metal surfaces. A mouse could easily chew through the vinyl wire coating or conduits, leaving bare wires exposed near metal plumbing pipes. Without proper grounding and electrical bonding, electricity can travel along the water pipes, but not necessarily metal duct work, posing the risk of different potentials should a person accidentally touch both.
When considering commercial and industrial structures, the risk of electrocution from metal conductivity is even higher, due to increased use of metal beams, studs, and other structural components. Practicing safe electrical installation practices, electrical bonding grounds each of these components, ensuring that in the rare event of a break in any given circuit, all metal surfaces carry the same potential. In short, electrical bonding creates a continuous circuit through all the major metal systems in a given building. Injury from electric shock is still possible but not as severe, since all components carry the same potential.