Ground or earth in a mains (AC power) electrical wiring system is a conductor that exists primarily to provide a low impedance path to the earth to prevent the buildup of voltages, static or transient (lightning), that may result in undue hazards to connected equipment or persons, and which in normal operation does not carry current. Earth grounding does little in helping to protect against faults which is accomplished through "bonding". Type F mains power plug & socket The term mains usually refers to the general purpose alternating current (AC) electrical power supply (as in “Ive connected the appliance to the mains”). The term is not usually used in the United States and Canada. ... City lights viewed in a motion blurred exposure. ... Electrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. ...

The term "ground" is used in Canada and the U.S.; the term "earth" is used in most of the rest of the English-speaking world. They are used synonymously here. For other uses, see United States (disambiguation) and US (disambiguation). ...

Neutral is a circuit conductor that may carry current in normal operation, and which is usually connected to earth (bonding). In house wiring, it is the center tap connection of the secondary winding of the power company's transformer. (See split phase.) As opposed to the "hot" wire(s) which carry the AC voltage, the neutral is the "cold" wire which is normally at zero volts. A split phase electricity distribution system is a 3-wire single-phase distribution system, commonly used in North America for single-family residential and light commercial (up to about 100 kVA) applications. ...

• In a polyphase or three-wire AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors, and similar phase spacing. By this definition, a circuit must have at least three wires for one to serve as a neutral.
• In the electrical trade, the conductor of a 2-wire circuit that is connected to the supply neutral point and earth ground is also referred to as the "neutral". This is formally described in the US and Canadian electrical codes as the "identified" circuit conductor.

The NEC and Canadian electrical code only define neutral as the first of these. In North American use, the second definition is used in less formal language but not in official specifications. In the UK the IET definition is a conductor connected to the supply system neutral point, which includes both these uses. The National Electric Code Handbook, 2005 edition The National Electrical Code (NEC), or NFPA 70, is a standard for the safe installation of electrical wiring and equipment. ... IET logo The Institution of Engineering and Technology (IET) is the professional institution for engineering and technology in the United Kingdom. ...

Earthing systems

The names for the following methods of earthing are those defined by IEC standards, which are used in Europe and many other regions. For a more detailed explanation, see earthing systems. Different terminology is used in North America, but the basic principles should be the same everywhere. The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ... // In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earths conductive surface. ...

Since the neutral point of a supply system is often connected to earth ground, neutral and earth are closely related. Various measures minimize the voltage difference between neutral and local earth ground. In some systems, the neutral and earth join together at the service intake (TN-C-S); in others, they run completely separately back to the transformer neutral terminal (TN-S), and in others they are kept completely separate with the house earth having its own rod and the neutral being rodded down to earth within the distribution network (TT). In a few cases, they are combined in house wiring (TN-C), but the dangers of broken neutrals (see below) and the cost of the special cables needed to mitigate this mean that it is rarely done nowadays. A TN-C-S earthing system is one where where earth and neutral are combined in the supply wiring but are separate in the installation. ... A TN-S earthing system is one where where earth and neutral run separately right back to the supply. ... In electricity supply a TT earthing system is one where there is no metallic connection at all between the customers earth and the neutral terminal of the transformer in the suppliers network. ... A TN-C earthing system is one where where earth and neutral are combined in the supply wiring and right through the install. ...

In the USA, the chassis/cases of some ovens and clothes dryers were grounded through their neutral wires, as a measure to conserve copper during the Second World War. This practice was removed from the NEC in the 1996 edition, but existing installations may still allow the chassis/case grounding of such appliances to be connected to the neutral conductor. Note that the NEC may be amended by local regulations in each state and city. This change to the NEC was implemented because ovens and dryers have components that use both 120 and 240 volts, and thus there is often current on the neutral wire. This differs from the protective grounding wire, which only carries current under fault conditions. A chassis connected to the grounding wire is generally safe because the heavier wire that feeds high-power appliances is less likely to break. The bonding connection between the neutral and grounding wires is only to be done at the main service panel. Oven depicted in a painting by Millet An oven is an enclosed compartment for heating, baking or drying. ... An electric clothes dryer A clothes dryer or tumble dryer is a household appliance that is used to remove the residual moisture from a load of clothing and other textiles, generally shortly after they are cleaned in a washing machine. ... Combatants Allied powers: China France Great Britain Soviet Union United States and others Axis powers: Germany Italy Japan and others Commanders Chiang Kai-shek Charles de Gaulle Winston Churchill Joseph Stalin Franklin Roosevelt Adolf Hitler Benito Mussolini Hideki Tōjō Casualties Military dead: 17,000,000 Civilian dead: 33,000... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ...

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 TN system where there is a direct connection from the installation earth to the transformer neutral, earthing will allow the branch circuit overcurrent protection (a fuse or circuit breaker) to detect the fault rapidly and interrupt the circuit. // In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earths conductive surface. ... 200 A Industrial fuse. ... A 2 pole miniature 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. ...

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. In electricity supply a TT earthing system is one where there is no metallic connection at all between the customers earth and the neutral terminal of the transformer in the suppliers network. ... Electrical impedance, or simply impedance, is a measure of opposition to a sinusoidal alternating electric current. ... A residual current device (RCD) A residual current device (RCD), or residual current circuit breaker (RCCB), is an electrical wiring device that disconnects a circuit whenever it detects that the flow of current is not balanced between the phase (hot) conductor and the neutral conductor. ...

Equipotential bonding

Equipotential bonding 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. 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. ...

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 pools. Wylex standard consumer unit fitted with rewirable fuses Modern Hager consumer unit fitted with MCBs and an RCD A consumer unit is a box of fuses or breakers, usually arranged in a single row. ... A fairly standard American circuit breaker panel manufactured by General Electric and using interchangeable circuit breakers A distribution board (known in the United States as a (circuit) breaker panel, panelboard, or load center or for old ones, fuse box) is a mounting enclosure for multiple electrical circuit breakers. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... This article does not cite any references or sources. ...

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.

Special measures may be required in barns used for milking dairy cattle. Very small differential voltages, not usually perceptible to humans, may cause low milk yield, or even mastitis (inflammation of the udder). So-called "tingle voltage filters" may be required in the electrical distribution system for a milking parlour. Mastitis is the inflammation of the mammalian breast caused by the blocking of the milk ducts while the mother is lactating (see breastfeeding). ...

Combining neutral with earth

Connecting the neutral to the equipment case provides some protection against faults/shorts, but may produce a dangerous voltage on the case if the neutral connection is broken.

Earths are commonly used in electricity supply companies' wiring and occasionally for fixed wiring in buildings and for some specialist applications where there is little choice like railways and trams. Since normal circuit currents in the neutral conductor can lead to objectionable or dangerous differences between local earth potential and the neutral and to protect against neutral breakages, special precautions such as frequent rodding down to earth, use of cables where the combined neutral and earth completely surrounds the phase conductor(s), and thicker than normal equipotential bonding must be considered to ensure the system is safe. 11kV/400V-230V transformer in an older suburb of Wellington, New Zealand Electricity distribution is the penultimate stage in the delivery (before retail) of electricity to end users. ... This article refers to public transport vehicles running on rails. ...

Portable appliances

In North American practice small portable equipment connected by a cord set may have only two conductors in the attachment plug. A polarised plug is used to maintain the identity of the neutral conductor into the appliance but it is never used as a chassis/case ground.

The small cords to lamps, etc., have one or more ridges or imbedded strings to identify the neutral conductor.

References

[1] Rick Gilmour et al., editor, Canadian Electrical Code Part I, Nineteenth Edition, C22.1-02 Safety Standard for Electrical Installations, Canadian Standards Association, Toronto, Ontario Canada (2002) ISBN 1-55324-690-X

[2] NFPA 70, National Electrical Code 2002, National Fire Protection Association, Inc., Quincy, Massachusetts USA, (2002). no ISBN

[3] IEE Wiring Regulations Regulations for Electrical Installations Fifteenth Edition 1981, The Institution of Electrical Engineers, (1981) Hitchin, Herts. United Kingdom

External links

Wikibooks has more about this subject:

Guide to electrical equipment for travellers

• http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf document from Paul Cook of the IET talking about why bonding metal accessories fed by plastic pipes is a bad idea.