Electrical bonding
Encyclopedia
Electrical bonding is the practice of intentionally electrically connecting all metallic non-current carrying items in a room or building as protection from electric shock
. If a failure of electrical insulation occurs, all metal objects in the room will have the same electrical potential, so that an occupant of the room 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.
Bonding refers to the fact that 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. This is done in the UK
because many buildings are supplied with a single phase supply cable
where the neutral and earth conductors are combined. Close to the electricity meter
this conductor is divided into two, the earth terminal and the wire going to the neutral
busbar
in the consumer unit
. In the event of a break in a neutral connection this earth terminal provided by the supply company
will be at a potential (relative to the true earth) which is the same as the live wire (phase wire) coming to the home.
Examples of articles that may be bonded include metallic water piping systems, gas piping, airplanes, ducts for central heating and air conditioning systems, and exposed metal parts of buildings such as hand rails, stairs, ladders, platforms and floors.
A person touching the un-earthed metal casing of an electrical device, while also in contact with a metal object connected to remote earth, is exposed to an electric shock
hazard if the device has a fault. If all metal objects are connected together, all the metal objects in the building will be at the same potential. It then will not be possible to get a shock by touching two 'earthed' objects at once.
Bonding is particularly important for swimming pools and fountains. In pools and fountains, any metallic object (other than conductors of the power circuit)over a certain size must be bonded to assure that all conductors are equipotential and do not provide a hazardous conductive path. Since it is buried in the ground, a pool can be a better ground than the electric panel ground. With all the conducting elements bonded, it is less likely that electric current will find a path through a swimmer. In concrete pools even the reinforcing bars of the concrete must be connected to the bonding system to ensure no dangerous potential gradients are produced during a fault.
system where there is a direct connection from the installation earth to the transformer neutral, 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 due to the lack of direct connection to the transformer
neutral, an RCD
(Residual-Current Device, sometimes known as a Residual Current Circuit Breaker or Ground Fault Circuit Interrupter) 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.
involves joining together metalwork that is or may be earthed so that it is at the same potential
(i.e., voltage) everywhere. Such is commonly used under transformer banks by power companies and under large computer installations.
Equipotential bonding is done from the Service Panel consumer unit
(also known as a 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 metal objects including metal fittings fed by plastic pipe (water in a thin pipe is actually a very poor conductor) are not required to be bonded. European and North American practices differ here; equipotential bonding in bathrooms is not required by North American codes, although it is required around swimming pool
s.
In Australia
and South Africa
, a house's earth cables must be connected both to an earthing rod/stake driven into the ground and also to the plumbing
.
Exact rules for electrical installations vary by country, locality, or supplying power company.
protection by allowing the current to pass through the airframe with minimum arcing. Bonding prevents dangerous static discharges in aircraft fuel tanks and hoses.
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
. If a failure of electrical insulation occurs, all metal objects in the room will have the same electrical potential, so that an occupant of the room 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.
Bonding refers to the fact that in a building with electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
it is normal for safety
Safety
Safety is the state of being "safe" , the condition of being protected against physical, social, spiritual, financial, political, emotional, occupational, psychological, educational or other types or consequences of failure, damage, error, accidents, harm or any other event which could be...
reasons to connect all metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
objects such as pipes
Piping
Within industry, piping is a system of pipes used to convey fluids from one location to another. The engineering discipline of piping design studies the efficient transport of fluid....
together to the mains
Mains
Mains may refer to:* Mains electricity * Mains power around the world* Electricity transmission* Public utility, "mains services", including electricity, natural gas, water, and sewage disposal...
earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
to form an equipotential zone. This is done in the UK
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
because many buildings are supplied with a single phase supply cable
Cable
A cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...
where the neutral and earth conductors are combined. Close to the electricity meter
Electricity meter
An electricity meter or energy meter is a device that measures the amount of electric energy consumed by a residence, business, or an electrically powered device....
this conductor is divided into two, the earth terminal and the wire going to the neutral
Ground and neutral
Since the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding of equipment and structures...
busbar
Busbar
In electrical power distribution, a bus bar is a strip of copper or aluminium that conducts electricity within a switchboard, distribution board, substation or other electrical apparatus....
in the consumer unit
Consumer unit
A consumer unit is a box of fuses or breakers, usually arranged in a single row. This is unlike a distribution board which has multiple rows of fuses or breakers and usually serves two or more locations, which may be split phase, two phase, two phases taken from three phase, or three phases.A...
. In the event of a break in a neutral connection this earth terminal provided by the supply company
Company
A company is a form of business organization. It is an association or collection of individual real persons and/or other companies, who each provide some form of capital. This group has a common purpose or focus and an aim of gaining profits. This collection, group or association of persons can be...
will be at a potential (relative to the true earth) which is the same as the live wire (phase wire) coming to the home.
Examples of articles that may be bonded include metallic water piping systems, gas piping, airplanes, ducts for central heating and air conditioning systems, and exposed metal parts of buildings such as hand rails, stairs, ladders, platforms and floors.
A person touching the un-earthed metal casing of an electrical device, while also in contact with a metal object connected to remote earth, is exposed to an electric shock
Electric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
hazard if the device has a fault. If all metal objects are connected together, all the metal objects in the building will be at the same potential. It then will not be possible to get a shock by touching two 'earthed' objects at once.
Bonding is particularly important for swimming pools and fountains. In pools and fountains, any metallic object (other than conductors of the power circuit)over a certain size must be bonded to assure that all conductors are equipotential and do not provide a hazardous conductive path. Since it is buried in the ground, a pool can be a better ground than the electric panel ground. With all the conducting elements bonded, it is less likely that electric current will find a path through a swimmer. In concrete pools even the reinforcing bars of the concrete must be connected to the bonding system to ensure no dangerous potential gradients are produced during a fault.
How the earth protects
In a system with a grounded (earthed) neutral, connecting all non-current-carrying metallic 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 TNEarthing system
In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to the Earth's conductive surface. The choice of earthing system can affect the safety and electromagnetic compatibility of the power supply, and regulations can vary considerably among...
system where there is a direct connection from the installation earth to the transformer neutral, earthing will allow the branch circuit over-current protection (a fuse
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
or circuit breaker
Circuit breaker
A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow...
) to detect the fault rapidly and interrupt the circuit.
In the case of a TT system where the impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...
is high due to the lack of direct connection to the transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
neutral, an RCD
Residual-current device
A Residual Current Device is a generic term covering both RCCBs and RCBOs.A Residual-Current Circuit Breaker is an electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized conductor and the return neutral conductor...
(Residual-Current Device, sometimes known as a Residual Current Circuit Breaker or Ground Fault Circuit Interrupter) 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.
Equipotential bonding
Equipotential bondingMultipoint ground
A Multipoint Ground is an alternate type of electrical installation that attempts to solve the Ground Loop and Mains hum problem by creating many alternate paths for electrical energy to find its way back to ground. The distinguishing characteristic of a multipoint ground is the use of many...
involves joining together metalwork that is or may be earthed so that it is at the same potential
Potential
*In linguistics, the potential mood*The mathematical study of potentials is known as potential theory; it is the study of harmonic functions on manifolds...
(i.e., voltage) everywhere. Such is commonly used under transformer banks by power companies and under large computer installations.
Equipotential bonding is done from the Service Panel consumer unit
Consumer unit
A consumer unit is a box of fuses or breakers, usually arranged in a single row. This is unlike a distribution board which has multiple rows of fuses or breakers and usually serves two or more locations, which may be split phase, two phase, two phases taken from three phase, or three phases.A...
(also known as a fuse box, breaker box, or distribution board
Distribution board
A distribution board is a component of an electricity supply system which divides an electrical power feed into subsidiary circuits, while providing a protective fuse or circuit breaker for each circuit, in a common enclosure...
) to incoming water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
and gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
services. It is also done in bathrooms where all exposed metal that leaves the bathroom including metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
pipes
Pipes
Pipes may refer to:*Pipe, a cylindrical conveyance*PIPES *Yahoo! Pipes*Pipeline *Bagpipes or Uilleann pipes*PIPE deal or private investment in public equity*Pipes , a Transformers character...
and the earths of electrical circuits must be bonded together to ensure that they are always at the same potential. Isolated metal objects including metal fittings fed by plastic pipe (water in a thin pipe is actually a very poor conductor) are not required to be bonded. European and North American practices differ here; equipotential bonding in bathrooms is not required by North American codes, although it is required around swimming pool
Swimming pool
A swimming pool, swimming bath, wading pool, or simply a pool, is a container filled with water intended for swimming or water-based recreation. There are many standard sizes; the largest is the Olympic-size swimming pool...
s.
In Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, a house's earth cables must be connected both to an earthing rod/stake driven into the ground and also to the plumbing
Plumbing
Plumbing is the system of pipes and drains installed in a building for the distribution of potable drinking water and the removal of waterborne wastes, and the skilled trade of working with pipes, tubing and plumbing fixtures in such systems. A plumber is someone who installs or repairs piping...
.
Exact rules for electrical installations vary by country, locality, or supplying power company.
Aircraft electrical bonding
In aircraft, electrical bonding prevents static electricity build-up that can interfere with radio and navigational equipment. Bonding also provides lightningLightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
protection by allowing the current to pass through the airframe with minimum arcing. Bonding prevents dangerous static discharges in aircraft fuel tanks and hoses.