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Equipotential bonding - commonly referred to as bonding -  is a very important measure in reducing the risk of equipment damage and personal injury. Bonding involves joining together all metalwork and conductive items that are or may be earthed so that it is at the same potential (voltage) everywhere. If a component failure occurs, all circuits and conductors in a bonded area will have the same electrical potential, so that an occupant of the area cannot touch two objects with significantly different potentials. Even if the connection to a distant earth ground is lost, the occupant will be protected from dangerous potential differences resulting in injury or death from electric shock.

The earthng system is an important part of a lightning protection system. The structure of buildings often includes reinforcing bars, steel frames and deck slabs as the main components. These components can also be used to form a low impedance grounding system.

Earthing vs. Bonding

Earthing is intended to limit the duration of voltages, while bonding is intended to limit the magnitude of voltages. The danger of electric shock due to indirect contact arises from the following voltages which may occur under earth fault conditions in an installation:

1. voltages between exposed conductive materials and other exposed conductive materials

2. voltages between peripheral conductive materials and other peripheral conductive materials

3. voltages between exposed conductive materials and peripheral conductive materials

4. voltages between exposed conductive materials and Earth, or peripheral conductive materials and Earth.

The purpose of earthing, where used for protective purposes within a building or other facility, is to limit the duration of the voltages in the above examples. This is achieved by the operation of a protective device (such as a fuse or circuit-breaker) under earth fault conditions, which removes the voltages by causing an automatic disconnection of the supply to the faulty circuit.

Without an adequate earthing system in place, the protective device could not operate as required under earth fault conditions. In contrast, the purpose of bonding is to limit the magnitude of the voltages in examples 1, 2 and 3 above. This is achieved by electrically connecting (bonding) those conductive parts.

Below - illustration showing a simple example of equipotential bonding.
Equipotential bonding on gates

PV Bonding Information
PV Bonding Information
click image for details of special
solar panel bonding requirements

Equipotential bonding is done from the switchboard (also known as the fuse box, breaker box, or distribution board) to incoming water and gas services. It is also done in bathrooms where all exposed metal that leaves the bathroom (including metal pipes and the earths of electrical circuits) must be bonded together to ensure that they are always at the same potential. Isolated conductive objects (including metal fittings fed by plastic pipe) do not need to be bonded.

In Australia, a house's earth cables must be connected both to an earthing rod driven into the ground and also to the plumbing.

 

Bonding of services
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Cadweld Exothermic Bonding
Cadweld Exothermic Bonding
Bonding of building framework
Exothermic Bonding of Building Framework
Earthing and bonding are an integral part of any modern electrical protection system. It is crucial in ensuring personnel safety, as well as providing reliable protection for vital equipment
and to minimise interruptions of service and costly down time.

The design at right identifies a typical grounding system and the components necessary for the job. However, this amounts to very little if the design is ineffective.

Click the image to view large size.
Earthing and Bonding Diagram

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