Earthing and bonding are two technical terms we come across when we deal with the safety aspect of an electrical system. We have all heard about earthing that is done for safety purposes during the electrical installation, but do we give much thought when it comes to electrical bonding. Both electrical bonding and earthing are essential in any electrical installation.
Let us have a basic understanding of Earthing and Bonding and their importance in our daily life.
What is Earthing?
Earthing is the process of letting the excess amount of charge which is created in an electrical system, flow directly to the surface of the earth. In an electrical system, an excess current may develop due to various reasons such as lightning, leakage, or other faults. The charge formed in a system due to the above reasons can cause damage to the devices, the complete system and to the persons who come in contact with it. So to avoid such heavy losses and provide safety, earthing is considered a critical part of every electrical system.
Why is Earthing important?
Earthing simply can be explained as providing a separate low resistance path for the excess current to flow into the earth. In the event of a power surge, it discharges all the excess current directly to the ground safeguarding the equipment and the people in contact with them. The requirements for an earthing system vary according to different situations; an industrial earthing system and residential earthing system differ based on the power usage, possible risks and the extent of safety needed for each. It can also vary from place to place concerning geographical conditions. For example, certain regions in the world are known to be majorly affected by lightning. In such places earthing plays a crucial role in lightning protection systems.
Types of Earthing
Earthing can be classified as system grounding, equipment grounding and functional earthing according to the purpose it serves.
System grounding deals with the earthing of all the structures and appliances within a system, like power distribution systems, telecommunication systems or residential/industrial buildings. While equipment grounding constraints to the safety of particular electrical appliances, protecting the device and personnel in contact with it from a fault event.
Functional earthing serves more than just safety. For example, in a telegraph line, it is used as a conductor saving the costs for a return wire over a long circuit and in a single wire power transmission system, it is a conductor and carries a load current.
Overall from a safety perspective earthing is considered as an electrical protection system. It ensures the security of people from electrical shock hazards, it safeguards the electrical appliances from damages caused by power surges and it also reduces the risk of fire due to current leakage.
Methods of Earthing
Common and simple earthing is done with ground rods, plates, electrodes, or grids of buried ground wire. Some non-electrical parts, like buried metal water or gas pipes, are also used as grounding electrodes in certain places. Special fittings join the grounding conductor to the grounding electrode. The size and type of conductor and the combination of grounding devices also vary according to conditions. Huge buildings and industrial systems may require a network of grounding devices, wires, grids, and conductors to satisfy their safety needs.
What is Bonding?
Bonding is the practice of electrically connecting all the exposed metallic surfaces of equipment, expected to be at zero potential always and letting them drain out to the ground to maintain a zero potential. If there is a potential difference between any two points in a system, and if a person comes in contact with both at the same time, there occurs an event of electric shock. Electrical bonding creates a low resistance path, to trip the overcurrent devices as quickly as possible. It also provides a path for static electricity and induced voltages to drain out, thus ensuring safety within the system.
Why is Bonding important?
All the metal parts of a system that can go live or develop potential should be bonded and connected to the ground.
For example, in a building, all the metallic objects are connected through bonding to the main earth for maintaining zero potential. Objects such as metallic water piping and gas piping systems, ducts for central heating and air conditioning systems, and exposed metal parts of buildings such as handrails, stairs, ladders all come under this list. This ensures that an equipotential zone is formed and anyone who comes in contact with these objects is safe from electrical shock hazards in case of current leakage or fault. When a person comes in contact with two conducting surfaces at different potentials, his body acts as a good conductor for current to pass through. Through electrical bonding, we make sure that such instances do not occur as all such surfaces are maintained at the same potential using bonds.
Another need for electrical bonding is to reduce touch potential, especially in the case of long conductive cable trays. When voltage is applied to a conductor, there will be a voltage drop across the length of the conductor in accordance with its resistance. Small differences in potential occur, based on the distance from the nearest grounding connection. If there is a difference in potential between a cable tray and a nearby staircase, someone who touches both of these at once might experience a shock. Having more frequent bonding connections will avoid these potential differences and thus decrease the chances of unintentional shocks from static or induced voltages.
Most commonly bonding is done with copper wires or copper alloy bonds. Electrical equipment usually have built-in bonding terminals or points. There are various types of bonds available in the market that can be used for bonding metal structures and copper cables to steel structures without making holes in these structures.
Earthing and bonding are two different ways of providing safety to electrical systems from sudden and unexpected leakage or discharge of current due to various reasons. Though earthing is a more common term we come across, bonding is also equally important in all electrical systems. At the same time, electrical bond alone does not ensure complete protection, but along with grounding, it helps to discharge the extra current to the ground thus making the system safe. Let us always consider safety aspects with keen importance and built safer electrical environments.
This article is part of our series of articles on Lightning Protection, Surge Protection & Earthing, you can read more with the following links:
Introduction to the basics of Lightning Protection and Earthing and the Standards (IEC 62305 and UL 467)
Surge Protection Devices (SPD)
Lightning Protection Zones and their Application to SPD Selection
How does a Lightning Arrester work?
Click here to view all of Axis’s Lightning Protection, Lightning Arresters and Earthing products.
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