Wiktor Wise
Equipotential bonding is a technique used to prevent equipment damage and personal injury by minimising the risk of electric shock. It involves connecting all exposed metal items not designed to carry electricity in a room or building to an earthing system, ensuring that all conductive parts have the same electrical potential. This is particularly important in areas with an increased risk of electric shock, such as bathrooms, kitchens, and swimming pools, where supplementary equipotential bonding is required. In these areas, all exposed metal, including pipes and electrical circuits, must be bonded together to prevent potential differences and the risk of electric shock.
Characteristics and Values of Equipotential Bonding
| Characteristics | Values |
|---|---|
| Definition | A technique for minimising the danger of equipment damage and personal injury |
| Purpose | To prevent electric shock and protect equipment and people by reducing the current flow between pieces of equipment at different potentials |
| Application | Connecting all metals and conductive goods to an earthing system (grounding system) so all of them have the same potential energy (voltage) |
| When to use | In areas with an additional risk of electric shock, such as bathrooms, saunas, kitchens, and showers |
| Benefits | Reduces the risk of equipment damage and personal injury, ensures safety, and achieves electromagnetic compatibility |
| Standards | BS 7671, IEC 364-4-41 Standard, GOST 13109-97, IEEE Standard 1048 |
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What You'll Learn
Electrical bonding
In a building, there are typically a number of services other than electrical supply that employ metallic connections in their design. In its most basic form, earthing and equipotential bonding prevent electric shock. For example, in a kitchen, if a dishwasher develops an electrical problem, a current is removed and sent down to the earthing path of the electrical equipment. Without an earth connection, the dishwasher’s metal exterior casing might become live. The goal of earthing is to reduce the contact voltage in such an instance. Equipotential bonding is a protective conductor that connects all at-risk metallic (conductive) pieces.
In a system with a grounded (earthed) neutral, connecting all non-current-carrying metal parts of equipment to earth ground at the main service panel will ensure that current due to faults (such as a "hot" wire touching the frame or chassis of the device) will be diverted to earth. In a TN system, earthing will allow the branch circuit over-current protection (a fuse or circuit breaker) to detect the fault rapidly and interrupt the circuit. In the case of a TT system where the impedance is high, 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) is desired.
The majority of electrical installations typically use Automatic Disconnection of Supply (ADS) as a protective measure against electric shock. Basic protection is provided by basic insulation of live parts or by barriers or enclosures, and fault protection is provided by protective earthing, protective equipotential bonding and ADS in the event of a fault.
In areas that carry an additional risk of electric shock to people, such as bathrooms, saunas, kitchens and showers, an additional equipotential bonding system (AEBS) shall be installed to provide a sufficient level of safety in case of emergency. The additional equipotential bonding system interconnects all conductive parts open for touch and external conductive parts, neutral and protective ground conductors of all equipment.
In modern apartment buildings, household appliances with metal elements can serve as conductors and have their own potential. Under normal operating conditions, this potential is close to zero and does not differ from the potential of surface and other surrounding objects. In the case of an accident, such as insulation breakage or the intake of potential through the pipes, the potential of such conductive parts may increase to several hundred volts. If a human touches two objects with different potentials at once, there is a risk of electric shock.
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Safety and protection
In simple terms, equipotential bonding aims to keep the potential of various conductive elements close to the same level. This is essential because when two objects have different potential voltages, a circuit is created between them, and if a person comes into contact with both objects, an electric current flows through them, resulting in an electric shock. By bonding all conductive parts together and to the Earth, this hazard is eliminated.
In buildings, this process of bonding is particularly important due to the presence of multiple conductive services, such as gas and water pipes, in addition to electrical supply lines. The main bonding occurs where these services enter the building, and it is crucial when these services are metallic. For example, if non-metallic pipes, such as plastic, are used, no main bonding is required. However, if the incoming pipes are plastic but connect to metal pipes within the building, bonding must be applied to the metal pipes.
Supplementary or additional bonding is also crucial in areas with an increased risk of shock, such as bathrooms, kitchens, and areas around swimming pools. In these spaces, all exposed metal, including pipes and electrical circuits, must be bonded together to ensure they are always at the same potential. This prevents hazardous situations where a person could touch two objects with significantly different potentials and receive an electric shock.
The use of equipotential bonding is a protective measure mandated by organisations like OSHA for individuals working with power generation, transmission, and distribution equipment. It ensures that workers within an equipotential zone are safe, as all accessible conductive parts are maintained at the same potential, minimising the risk of electric shock.
To ensure the effectiveness of equipotential bonding, continuity testing is necessary to verify that the bonding conductors are continuous and provide a low ohmic value. This testing is essential for safety, as any conductive parts without an effective connection to Earth will not create an equipotential zone, increasing the risk of electric shock in the event of a fault.
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Earthing and grounding
Earthing refers to the connection of non-current-carrying metal parts of equipment to the earth ground at the main service panel. This ensures that any current due to faults is diverted to the earth, protecting users from electric shock. It is a basic safety measure in electrical installations, preventing metal casings from becoming live in the event of an electrical problem.
Grounding, or equipotential bonding, is the process of connecting all exposed metal items in a room or building that are not designed to carry electricity. This includes conductive parts in equipment housings and external conductive elements outside of equipment housings. By bonding these metal parts together, they are maintained at the same potential, limiting voltage differences and reducing the risk of electric shock.
In buildings, equipotential bonding is commonly performed on incoming water and gas services, as well as in bathrooms, kitchens, and other areas with an increased risk of shock. It is also important for lightning protection, allowing current to pass through with minimal arcing.
Continuity testing is necessary to ensure that protective bonding conductors are continuous and provide a low enough ohmic value to be effective.
Overall, earthing and grounding are crucial for ensuring the safety of electrical installations, protecting both equipment and individuals from the dangers of electric shock and voltage differences.
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Reducing voltage differences
The process of providing equipotential bonding of non-electrical equipment is known as electrical bonding. It involves connecting all non-current-carrying metal parts of equipment to the Earth's conductive surface. This is done to ensure safety and prevent electric shock.
Voltage differences can be reduced through various methods, including the use of electrical circuits, resistors, transformers, and voltage regulators.
One common method is to use a voltage divider circuit, which allows you to obtain any desired voltage level. This can be achieved by using resistors of equal value in series and placing a jumper wire between them. The voltage at the point of the jumper wire will then be half of the original voltage. For example, if you have a 5V circuit and want to reduce it to 3V, you can use a 10KΩ resistor as your R1 resistor and calculate the value of R2 using the formula: R2 = (V)(R1)/ (VIN - V). In this case, R2 would be 15KΩ.
Another method is to use a transformer, which works by wrapping a wire around a metal core to create a magnet. By changing the number of windings around the core, you can alter the voltage. For instance, if you want to halve the voltage, use half the windings on the second core compared to the first. Conversely, doubling the number of windings will double the voltage.
Additionally, voltage regulators like buck, boost, or buck/boost regulators can be used to increase or decrease voltage efficiently. A specific type of circuit called a charge pump can boost the voltage above the original level by pumping charge into specific parts of the circuit.
In power distribution systems, a higher voltage can be used to transmit a given amount of power with a lower voltage drop. According to Ohm's law, the voltage drop can also be reduced by lowering the overall resistance, which can be achieved by increasing the diameter of the conductor between the source and the load.
These techniques can help reduce voltage differences and improve the efficiency and safety of electrical systems.
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Preventing equipment damage
In simple terms, equipotential bonding is an electrical connection that keeps the potential of several exposed and extraneous conducting elements close to the same. An earthed equipotential zone is created when exposed conductive parts and extraneous conducting parts are maintained at the same or very similar potential by bonding. This is to ensure that the potential difference between accessible exposed conductive parts does not occur under fault situations.
In a building, there are often services other than the electrical supply that employ metallic connections in their design. These include gas and water pipes. When numerous earthed items are connected, the magnitude of their voltage is limited, and a harmful potential difference is avoided. This is important because if a worker touches two objects with different voltages, a current will flow through them, which can be fatal.
In the context of non-electrical equipment, equipotential bonding is particularly relevant in areas with an increased risk of electric shock, such as bathrooms, kitchens, and swimming pools. In these areas, supplementary or additional equipotential bonding (earthing) is required. This involves bonding all exposed metal, such as metal pipes and the earths of electrical circuits, to ensure they are always at the same potential.
To ensure safety, it is crucial to follow regulations and standards, such as BS 7671, when installing and maintaining equipotential bonding systems. This includes performing continuity testing to verify the electrical continuity of protective bonding conductors and ensuring that all connections are secure and provide a sufficiently low ohmic value.
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Frequently asked questions
Equipotential bonding is an electrical connection that keeps the potential of several exposed and extraneous conducting elements close to the same. It is also referred to as bonding or EPB.
Equipotential bonding is necessary to prevent equipment damage and personal injury. It protects against electric shock by limiting the magnitude of the voltages.
Equipotential bonding of non-electrical equipment involves connecting all non-current-carrying metal parts of the equipment to an earthing system. This ensures that the potential difference between accessible exposed conductive parts does not occur under fault situations.
Equipotential bonding is used in areas with an increased risk of electric shock, such as bathrooms, kitchens, and swimming pools. It is also used in lightning protection systems and in aircraft to prevent static electricity build-up.
