Electrical bonding ensures that all conductive surfaces have the same electrical potential as the Earth. This eliminates the risk of an electrical shock, if you should come in contact with a device with an insulation fault.
Grounding ensures that in the event of a short circuit, or insulation fault a current protection device (circuit breaker, fuse) is tripped and power is shut down.
Bonding is when all metallic objects in a building or a particular room are joined together electrically to protect against electric shock.
In the case of a failure in the electrical insulation, all the metal objects would have an equal electrical potential. So, even if the earth ground connection is lost, you will still be protected from dangerous differences in potential. It is the differences in potential that cause an electrical shock.
Examples of objects that could be bonded include heating and cooling ducts, gas piping and water pipes, as well as metal parts of a building that are exposed such as metal stairs, rails and platforms.
If you are in contact with a metal object that is connected to remote earth, and then touch a non-earthed metal casing of an electrical device, you are at risk of electric shock if that device happens to have a fault.
When all metal objects are electrically connected, they are all at an equal potential. So, it is then impossible to get a shock when touching two ‘earthed’ objects at the same time.
Bonding is especially important in areas where electricity and water have to work together such as decorative fountains, swimming pools and bathrooms. In fountains and pools, metallic objects (except for power circuit conductors) over a certain size have to be bonded to make sure all conductors have equal potential, and do not provide a conductive path that can become hazardous.
A in-ground pool can actually be a better ground than an electric panel ground because it has direct contact with the earth, since most of it is buried. By bonding all the conducting elements, the chance of an electric current passing through someone in the pool is very unlikely.
In concrete pools, even the bars used to reinforce the concrete have to be part of the bonding system, to make certain that in case of a fault there aren’t any dangerous potential gradients produced.
Equal potential bonding is when you join together metal objects that are, or may be earthed in order to equalize the potential (voltage for example) across all the surfaces.
This technique is regularly used by power companies beneath transformer banks and underneath large computer installations. As with most electrical rules, how and where you install the electrical bonding varies by country, region or power company.
In residential buildings, you would do the electrical bonding from the service panel (also know as the distribution board, breaker box or fuse box) to the incoming gas and water services. You would also bond any exposed metal leaving the bathroom, which includes metal pipes and electrical circuit earths.
These must be bonded together to make sure they always have equal potential. However, isolated metal objects, such as metal fittings connected to plastic piping, don’t need to be bonded.
The practices in Europe and North America differ when it comes equal potential bonding in bathrooms. North American codes don’t make this practice mandatory, although it is necessary around swimming pools.
In Australia and South Africa, codes state that the earth cables on a house must be connected to an earthing rod embedded in the ground, as well as to the gas and plumbing pipes.
Electrical bonding in airplanes prevents static electricity from building up, which can have hazardous effects on the radio and navigational equipment.
By bonding, the plane is also provided protection from lightning because the current is allowed to pass through the frame with a minimum amount of arcing.
It also prevents dangerous electrostatic discharges in the aircraft’s fuel tank and hoses.