Editing Mains electricity (section)

== Voltage levels ==
[[File:World Map of Mains Voltages and Frequencies, Detailed.svg|thumb|450px|World map of mains voltages and frequencies, simplified to country level]]

Most of the world population ([[Europe]], [[Africa]], [[Asia]], [[Australia]], [[New Zealand]], and much of [[South America]]) use a supply that is within 6% of 230&nbsp;V. In the [[United Kingdom]]<ref>{{cite web |last1=Halliday |first1=Chris |last2=Urquhart |first2=Dave |title=Voltage and Equipment Standard Misalignment |url=http://www.powerlogic.com.au/Attachments/Voltage%20and%20Equipment%20Standard%20Misalignment%20PaperV.pdf |url-status=dead |archive-url=https://web.archive.org/web/20180311234438/http://powerlogic.com.au/Attachments/Voltage%20and%20Equipment%20Standard%20Misalignment%20PaperV.pdf |archive-date=11 March 2018 |access-date=14 March 2014 |website=powerlogic.com}}</ref> the nominal supply voltage is 230&nbsp;V +10%/−6% to accommodate the fact that most transformers are in fact still set to 240&nbsp;V. The 230&nbsp;V standard has become widespread so that 230&nbsp;V equipment can be used in most parts of the world with the aid of an [[adapter]] or a change to the equipment's plug to the standard for the specific country.

The [[United States]] and [[Canada]] use a supply voltage of 120&nbsp;volts ± 6%. [[Japan]], [[Taiwan]], [[Saudi Arabia]], [[North America]], [[Central America]] and some parts of northern South America use a voltage between 100&nbsp;V and 127&nbsp;V. However, most of the households in Japan equip split-phase electric power like the United States, which can supply 200&nbsp;V by using reversed phase at the same time. [[Brazil]] is unusual in having both 127&nbsp;V and 220&nbsp;V systems at 60&nbsp;Hz and also permitting interchangeable plugs and sockets.<ref name="brazil">{{cite web |title=Power plug, socket & mains voltage in Brazil |url=https://www.worldstandards.eu/electricity/plug-voltage-by-country/brazil/ |access-date=2020-11-27 |website=WorldStandards |language=en-GB}}</ref> [[Saudi Arabia]] and [[Mexico]] have mixed voltage systems; in residential and light commercial buildings both countries use 127&nbsp;volts, with 220&nbsp;volts at 60&nbsp;Hz in commercial and industrial applications. The Saudi government approved plans in August 2010 to transition the country to a totally 230/400-volt 60&nbsp;Hz system.<ref>{{cite web |title=Voltage in Saudi Arabia - Electricity Supply and Power Quality Overview |url=https://www.sinalda.com/world-voltages/middle-east/voltage-saudi-arabia/ |access-date=2020-11-27 |website=Sinalda |language=en-GB}}</ref>

=== Measuring voltage ===
A distinction should be made between the voltage at the point of supply (nominal voltage at the point of interconnection between the electrical utility and the user) and the voltage rating of the equipment (utilization or load voltage). Typically the utilization voltage is 3% to 5% lower than the nominal system voltage; for example, a nominal 208&nbsp;V supply system will be connected to motors with "200&nbsp;V" on their nameplates. This allows for the [[voltage drop]] between equipment and supply.{{Citation needed|date=December 2019}} Voltages in this article are the nominal supply voltages and equipment used on these systems will carry slightly lower nameplate voltages. Power distribution system voltage is nearly sinusoidal in nature. Voltages are expressed as [[root mean square]] (RMS) voltage. 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 and storms and other unusual conditions may cause even larger transient variations. In general, power supplies derived from large networks with many sources are more stable than those supplied to an isolated community with perhaps only a single generator.

=== Choice of voltage ===
{{Main|Mains electricity by country}}

The choice of supply voltage is due more to historical reasons than optimization of the electric power distribution system—once a voltage is in use and equipment using this voltage is widespread, changing voltage is a drastic and expensive measure. A 230&nbsp;V distribution system will use less conductor material than a 120&nbsp;V system to deliver a given amount of power because the current, and consequently the resistive loss, is lower. While large heating appliances can use smaller conductors at 230&nbsp;V for the same output rating, few household appliances use anything like the full capacity of the outlet to which they are connected. Minimum wire size for hand-held or portable equipment is usually restricted by the mechanical strength of the conductors.

Many areas, such as the US, which use (nominally) 120&nbsp;V, make use of [[Split-phase electric power|three-wire, split-phase]] 240&nbsp;V systems to supply large appliances. In this system a 240&nbsp;V supply has a centre-tapped neutral to give two 120&nbsp;V supplies which can also supply 240&nbsp;V to loads connected between the two line wires. Three-phase systems can be connected to give various combinations of voltage, suitable for use by different classes of equipment. Where both single-phase and three-phase loads are served by an electrical system, the system may be labelled with both voltages such as 120/208 or 230/400&nbsp;V, to show the line-to-neutral voltage and the line-to-line voltage. Large loads are connected for the higher voltage. Other three-phase voltages, up to 830&nbsp;volts, are occasionally used for special-purpose systems such as oil well pumps. Large industrial motors (say, more than 250&nbsp;hp or 150&nbsp;kW) may operate on medium voltage. On 60&nbsp;Hz systems a standard for medium voltage equipment is 2,400/4,160&nbsp;V whereas 3,300&nbsp;V is the common standard for 50&nbsp;Hz systems.

=== Standardization ===
Until 1987, mains voltage in large parts of Europe, including Germany, Austria and Switzerland, was {{val|220|22|u=V}} while the UK used {{val|240|14.4|u=V}}. Standard ISO&nbsp;IEC&nbsp;60038:1983 defined the new standard European voltage to be {{val|230|23|u=V}}. From 1987 onwards, a step-wise shift towards {{val|230|+13.8|-23|u=V}} was implemented. From 2009 on, the voltage is permitted to be {{val|230|23|u=V}}.<!-- translation from the German article, see there for additional sources to carry over --><ref>CENELEC Harmonisation Document HD 472 S1:1988</ref><ref>British Standard BS 7697: Nominal voltages for low voltage public electricity supply systems – (Implementation of HD 472 S1)</ref> No change in voltage was required by either the Central European or the UK system, as both 220&nbsp;V and 240&nbsp;V fall within the lower 230&nbsp;V tolerance bands (230&nbsp;V ±6%). Usually the voltage of 230&nbsp;V ±3% is maintained. Some areas of the UK still have 250&nbsp;volts for legacy reasons{{Citation needed|date=January 2025}}, but these also fall within the 10% tolerance band of 230&nbsp;volts. In practice, this allowed countries to have supplied the same voltage (220 or 240&nbsp;V), at least until existing supply transformers are replaced. Equipment (with the exception of [[Incandescent light bulb|filament bulbs]]) used in these countries is designed to accept any voltage within the specified range.

In 2000, [[Australia]] converted to 230&nbsp;V as the nominal standard with a tolerance of +10%/−6%,<ref>{{cite book |author1=Hossain, J. |url=https://books.google.com/books?id=tI_EBAAAQBAJ&q=as60038&pg=PA71 |title=Renewable Energy Integration: Challenges and Solutions |author2=Mahmud, A. |date=29 January 2014 |publisher=Springer |isbn=978-9814585279 |page=71 |access-date=13 January 2018}}</ref> this superseding the old 240&nbsp;V standard, AS&nbsp;2926-1987. The tolerance was increased in 2022 to ±&nbsp;10% with the release of AS&nbsp;IEC&nbsp;60038:2022.<ref>{{Cite web |title=Electrical Contractor Update - Issue 04 - February 2023 |url=https://us5.campaign-archive.com/?u=69932807d57ffb9c816b93a84&id=866a5eb399 |access-date=2024-03-04 |website=us5.campaign-archive.com}}</ref> The utilization voltage available at an appliance may be below this range, due to voltage drops within the customer installation. As in the UK, 240&nbsp;V is within the allowable limits and "240&nbsp;volt" is a synonym for mains in [[Australian English|Australian]] and [[British English]].

In the United States<ref>[[American National Standards Institute|ANSI]]&nbsp;C84.1: [http://www.nema.org/stds/c84-1.cfm American National Standard for Electric Power Systems and Equipment – Voltage Ratings (60 Hertz)] {{webarchive|url=https://web.archive.org/web/20070727234316/http://www.nema.org/stds/c84-1.cfm|date=27 July 2007}}, NEMA (costs $95 for access)</ref><ref name="PG&E_1999">{{cite web |date=1999-01-01 |title=Voltage Tolerance Boundary |url=https://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/voltage_tolerance.pdf |url-status=live |archive-url=https://web.archive.org/web/20191110020717/https://www.pge.com/includes/docs/pdfs/mybusiness/customerservice/energystatus/powerquality/voltage_tolerance.pdf |archive-date=2019-11-10 |access-date=2019-11-22 |publisher=PG&E}}</ref> and Canada,<ref>[[CSA Group|CSA]]&nbsp;CAN3-C235-83: Preferred Voltage Levels for AC Systems, 0 to 50,000&nbsp;V</ref> national standards specify that the nominal voltage at the source should be 120&nbsp;V and allow a range of 114&nbsp;V to 126&nbsp;V ([[Root mean square|RMS]]) (−5% to +5%). Historically, 110&nbsp;V, 115&nbsp;V and 117&nbsp;V have been used at different times and places in North America.{{Citation needed|date=November 2022}} Mains power is sometimes spoken of as 110&nbsp;V; however, 120&nbsp;V is the nominal voltage.

In [[Japan]], the electrical power supply to households is at 100 and 200&nbsp;V. Eastern and northern parts of [[Honshu|Honshū]] (including [[Tokyo]]) and [[Hokkaido|Hokkaidō]] have a frequency of 50&nbsp;Hz, whereas western Honshū (including Nagoya, Osaka, and Hiroshima), [[Shikoku]], [[Kyushu|Kyūshū]] and [[Okinawa (city)|Okinawa]] operate at 60&nbsp;Hz. The boundary between the two regions contains four back-to-back [[High-voltage direct current|high-voltage direct-current]] (HVDC) substations which interconnect the power between the two grid systems; these are [[Shin-Shinano Frequency Converter|Shin Shinano]], [[Sakuma Dam#HVDC frequency converter|Sakuma Dam]], [[Minami-Fukumitsu Frequency Converter|Minami-Fukumitsu]], and the [[Higashi-Shimizu Frequency Converter]]. To accommodate the difference, frequency-sensitive appliances marketed in Japan can often be switched between the two frequencies.