MAINS ELECTRICITY

The term 'mains' usually refers to the general purpose alternating current (AC) electrical power supply (as in “I've connected the appliance to the mains”). The term is not usually used in the United States and Canada.
In the United States, mains power has a variety of names. It is often called 'household power', 'household electricity', 'domestic power', 'wall power', 'line power', 'AC power', or 'grid power'.
In Canada, any of the American terms for mains power can be used, but it may also be called 'hydro' because much of the Canadian electrical generating capacity is hydroelectric.
Worldwide, many different mains power systems are found for the operation of household and light commercial electrical appliances and lighting. The different systems are characterized by:

★ Voltage,

★ Frequency,

★ wall sockets (receptacles) used,

★ Grounding (earthing) system used, if any.
These parameters vary among regions, but the voltages are generally in the range 100–240 V, and the two commonly used frequencies are 50 Hz and 60 Hz.
Some territories use different standards than the countries they belong to (such as Hong Kong). Foreign enclaves, such as large industrial plants or overseas military bases, may have a different standard voltage and frequency from the surrounding areas. Some city areas may use different standards from the surrounding countryside. Regions in an effective state of anarchy may have no central electrical authority, with electric power provided by incompatible private sources.
Many other combinations of voltage and utility frequency, including direct current, were formerly used, with frequencies between 25 Hz and 100 Hz and voltages from 100 to 250 V. The modern combinations of 230 V/50 Hz and 120 V/60 Hz did not apply in the first few decades of the 20th Century and are still not universal.
Industrial plants with polyphase power systems will have different, higher, voltages installed for large equipment (and different sockets and plugs), but the common voltages listed here would still be found for lighting and portable equipment.

Contents

Voltage levels

History of voltage and frequency

Frequency stability

Powerline communications

References

See also

Voltage levels

Distinction should be made between the voltage at the point of supply (nominal system voltage) and the voltage rating of the equipment (utilization voltage). Typically the utilization voltage is 3 to 5 % lower than the nominal system voltage; for example, a nominal 208 V supply system will be connected to motors with "200 V" on their nameplates. This allows for the voltage drop between equipment and supply. Voltages in this article are the nominal supply voltages and equipment used on these systems will carry slightly lower nameplate voltages.
The choice of utilization voltage is governed more by tradition than by optimization of the distribution system. In theory a 230 V distribution system will use less conductor material to deliver a given quantity of power. Incandescent lamps for 120 V systems are more efficient and rugged than 230 V lamps, while large heating appliances can use smaller conductors at 230 V for the same output rating. Practically speaking, few household appliances use anything like the full capacity of the outlet to which they are connected. Minimum wire sizes for hand-held or portable equipment is usually restricted by the mechanical strength of the conductors. One may observe that both 230 V system countries and 120 V system countries have extensive penetration of electrical appliances in homes. National electrical codes prescribe wiring methods intended to minimize the risk of electric shock or fire.
Many areas using (nominally) 120 V make use of three-wire, single-phase 240 V systems to supply large appliances. Three-phase systems can be connected to give various combinations of voltage, suitable for use by different classes of equipment.
Most European countries are gradually moving towards a 230 volt standard. The European Union^[1] (including the UK^[2]) has now officially harmonized on a low voltage single-phase supply RMS (Root Mean Square) voltage of 230 V ±10%, with a frequency of 50 Hz^[3]. For a transition period (1995–2008), countries who previously used 220 V will use a narrower asymmetric tolerance range of 230 V +6% −10% and those (like the UK) who previously used 240 V will use 230 V +10% −6%^[4]. Note that in practice no change in voltage is required by either system as both 220V and 240V fall within the lower 230 V tolerance bands (230 V ±6%).
Following voltage harmonization all electricity supply within the EU is now nominally 230 V ± 10% (though some countries have stricter specifications: for example, the UK specifies 230 V +10% −6%). In practice this means that countries such as the UK that previously supplied 240 V continue to do so, and those that previously supplied 220 V continue to do so. However equipment should be designed to accept any voltages within the specified range, and in practice most do so.
In the United States^[5] and Canada^[6], national standards dictate that utilities supply the nominal voltage within −5% to +5%. These standards specify that the nominal voltage at the source of supply should be nominal 120 V and allow a range of 114 to 126 V (-5% to +5%). Historically 110, 115 and 117 volts have been used at different times and places in North America.
Voltage tolerances are for steady-state operation; momentary heavy loads, or switching operations in the power distribution network, may cause short-term deviations out of the tolerance band. In general, power supplies derived from large networks with many sources will be more stable than those supplied to an isolated community with perhaps only a single generator.
All European and most African and Asian countries use a supply that is within 10% of 230 V, whereas Japan, North America and some parts of South America use a supply between 100 and 127 V.
As of the year 2000, Australia has converted to 230 V as the nominal standard with a tolerance of +10% -6%.^[7], this superseding the old 240 V standard, AS2926-1987.^[8] Like the UK, 240 V is within the allowable limits and “240 volt” spoken as “two forty volt” remains a synonym for mains in Australian and British English.
In Japan, the electrical power supply to households is at 100 V. Eastern and northern parts of Honshū (including Tokyo) and Hokkaidō have a frequency of 50 Hz, whereas western Honshu (including Nagoya, Osaka, and Hiroshima), Shikoku, Kyūshū and Okinawa operate at 60 Hz. To accommodate the difference, appliances marketed in Japan can often be switched between the two frequencies.

History of voltage and frequency

Voltage & frequency around the world

A 50 Hz ±5 Hz vibrating-reed mains frequency meter for 220 V (this device was made in Czechoslovakia in 1967)

The system of three-phase alternating current electrical generation and distribution was invented by several persons in the 19th Century including Nikola Tesla. He considered 60 Hz the best frequency for alternating current (AC) power distribution, and 240 V as the best voltage for long distribution circuits. Thomas Edison developed direct current (DC) systems at 110 V and this was claimed to be safer. For more information about the early battles between proponents of AC and DC supply systems see War of Currents. The 110 volt level was chosen to make high-resistance carbon filament lamps practical and economically competitive with gas lighting. While higher voltages would reduce the current required for a given quantity of lamps, the filaments would become increasingly fragile and short-lived; Edison selected voltages around 100 as a comprimise between distribution costs and lamp costs.
In the 1880's only carbon-filament incandescent lamps were available, designed for a voltage of around 100 volts. Later metal filament lamps became feasible. In 1899, the Berliner Electricitäts-Werk (BEW), a Berlin electrical utility, decided to greatly increase its distribution capacity by switching to 220 volt nominal distribution, taking advantage of the higher voltage capability of metal filament lamps. The company was able to offset the cost of converting the customer's equipment by the resulting saving in distribution conductors cost. This became the model for electrical distribution in Germany and the rest of Europe and the 220-volt (later 230-volt) system became common. North American practice remained with voltages near 110 volts for lamps. ^[9]
In 1883 Edison patented a three wire distribution system to allow DC generation plants to serve a wider radius of customers. This saved on copper costs since lamps were connected in series on a 220 volt system, with a neutral conductor connected between to carry any unbalance between the two sub-circuits. This was later adapted to AC circuits. Most lighting and small appliances ran on 120 V, while big appliances could be connected to 240 V. This system saved copper and was backward-compatible with existing appliances. Also, the original plugs could be used with the revised system.
Many different power frequencies were used in the 19th century, but early in the 20th century most power was produced at 60 Hz (North America) or 50 Hz (Europe and most of Asia). The first units at the Niagara Falls generating station produced 25 Hz power and some early systems used 25 Hz. Canadian 25 Hz residential customers were converted from 25 Hz service to 60 Hz starting in 1949, a project that ran for about 10 years. Prior to the conversion, special filters would be placed onto the ends of fluorescent lights to prevent the flicker from being visible. A few industrial customers, and the Toronto subway (underground) system, still use 25 Hz power in the Niagara Region of Ontario and Western New York, from the hydro-electric plants on the Niagara River or from frequency changers operated off the 60 Hz network.
Implementation of the National Grid in the United Kingdom starting in 1926 compelled the standardization of frequencies among the many interconnected electrical service providers. Notably, the large
NESCO network in the north-east part of England was converted at great expense from 40 Hz to 50 Hz to match the national grid.
The German company AEG (descended from a company founded by Edision in Germany) built the first European generating facility to run at 50 Hz, allegedly because the number 60 did not fit into the numerical unit sequence of 1, 2, 5…. At that time, AEG had a virtual monopoly and their standard spread to the rest of the continent. In Britain, differing frequencies (including 25 Hz, 40 Hz, and DC) proliferated, and the 50 Hz standard was completely established only after World War II. In an interesting symmetry, parts of California used 50 Hz power and did not standardize on 60 Hz until the late 1940's.
Some traction power networks for railway use in Europe operate at 16-2/3 Hz, for propulsion of electric trains.

Frequency stability

Frequency stabilization of large interconnected power systems allow line-operated clocks to keep accurate time. Network operators will regulate the daily average frequency so that clocks stay within a few seconds of correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. In continental Europe the deviation between synchronous time and actual is calculated at 8 a.m. each day, and the frequency normally raised or lowered by 0.02% from 50 Hz as needed.^[10] In Canada the deviation is constantly monitored and whenever the error exceeds 2 seconds a correction of +/- 0.02 Hz (0.033%) is applied.^[11] A real-time frequency meter for power generation in the United Kingdom is available online.[1] Smaller power systems may not maintain frequency with the same degree of accuracy.

Powerline communications

'Power line communication (PLC)', also called mains communication, power line telecoms (PLT), powerband or power line networking (PLN) or power area networking (PAN) are terms describing several different systems for using power distribution wires for simultaneous distribution of data. The carrier can communicate voice and data by superimposing an analog signal over the standard 50 or 60 Hz alternating current (AC). It includes Broadband over Power Lines (BPL) with data rates sometimes above 1 Mbit/s and Narrowband over Power Lines with much lower data rates.
A short-range form of power-line carrier is used for home automation and intercoms.

References

"
1. CENELEC Harmonization Document HD 472 S1:1988
2. Electricity Supply (Amendment) (No. 2) Regulations 1994 (Statutory Instrument 1994 No. 3021), which amend the The Electricity Supply Regulations 1988 (Statutory Instrument 1988 No. 1057)
3. CENELEC standard EN 50160: Voltage characteristics of electricity supplied by public distribution systems
4. British Standard BS 7697: Nominal voltages for low voltage public electricity supply systems — (Implementation of HD 472 S1)
5. ANSI C84.1: American National Standard for Electric Power Systems and Equipment—Voltage Ratings (60 Hertz)
6. CSA C3-235: Preferred Voltage Levels for AC Systems, 0 to 50 000 V
7. AS60038-2000 Standards Australia - ''Standard Voltages''
8. SAI Global
9. Thomas P. Hughes, ''Networks of Power: Electrification in Western Society 1880-1930'', The Johns Hopkins University Press,Baltimore 1983 ISBN 0-8018-2873-2 pg. 193
10. Load Frequency Control and Performance
11. B.C. Hydro e-mail

See also

★ Domestic AC power plugs and sockets

★ Electricity

★ Energy meter

★ Potential difference

★ Power connector

★ Three-phase electric power