Electrical bonding

In a building with electricity, it is normal for safety reasons to connect all metal objects such as pipes together to the mains earth to form an equipotential zone.

Examples of articles that may be bonded include metallic water piping systems, gas piping, ducts for central heating and air conditioning systems, and exposed metal parts of buildings such as handrails, stairs, ladders, platforms, and floors.

In the case of a TT system where the impedance is high due to the lack of direct connection to the transformer neutral, a residual-current device (RCD) must be used to provide disconnection.

RCDs are also used in other situations where rapid disconnection of small earth faults (including a human touching a live wire by accident, or damage) is desired.

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.