View source for Low voltage

{{Short description|Low amounts of electrical volts}}
In [[electrical engineering]], '''low voltage''' is a relative term, the definition varying by context.  Different definitions are used in [[electric power]] transmission and distribution compared with electronics design. [[Electrical code|Electrical safety codes]] define "low voltage" circuits that are exempt from the protection required at higher voltages. These definitions vary by country and specific codes or regulations.

== IEC Definition==
{| class="wikitable"
|-
! Voltage range
! AC RMS voltage (V)
! DC voltage (V)
! Defining risk
|-
! High voltage (HV)
| > 1000<ref name="IEC 61140:2016">IEC 61140:2016 Chapter 4.2</ref>{{note label|app|a|a}}
| > 1500<ref name="IEC 61140:2016" />{{note label|app|a|a}}
| Electrical arcing
|-
! Low voltage (LV) 
| ≤ 1000<ref name="IEC 61140:2016" />{{note label|app|a|a}}
| ≤ 1500<ref name="IEC 61140:2016" />{{note label|app|a|a}}
| Electrical shock
|-
! Extra Low voltage (ELV) 
| ≤ 50<ref name="IEC 61140:2016" />{{note label|app|a|a}}
| ≤ 120<ref name="IEC 61140:2016" />{{note label|app|a|a}}
| Electrical fire
|}
{{note label|app|a|a}} May depend on the applicable standard used.

The [[International Electrotechnical Commission]] (IEC) Standard IEC 61140:2016 defines Low voltage as 0 to 1000 V [[Alternating current|AC]] [[Root mean square|RMS]] or 0 to 1500 V [[Direct current|DC]]<ref name="IEC 61140:2016" /> Other standards such as IEC 60038 defines ''supply system low voltage'' as voltage in the range 50 to 1000&nbsp;V&nbsp;AC or 120 to 1500&nbsp;V&nbsp;DC in ''IEC Standard Voltages''<ref>[https://webstore.iec.ch/publication/153''IEC Standard Voltages,'' IEC 60038]</ref> which defines power distribution system voltages around the world.

In electrical power systems ''low voltage'' most commonly refers to the [[mains electricity|mains voltage]]s as used by domestic and light industrial and commercial consumers. "Low voltage" in this context still presents a risk of [[Electrical injury|electric shock]], but only a minor risk of [[electric arc]]s through the air.

==United Kingdom==
*British Standard [[BS 7671]], ''Requirements for Electrical Installations. IET Wiring Regulations'',<ref>''[https://shop.bsigroup.com/ProductDetail?pid=000000000030342613 Requirements for Electrical Installations. IET Wiring Regulations]'', BS 7671, [[BSI Group|British Standards Institute]] (BSI), London, 2018+A1:2020</ref> defines ''supply system low voltage'' as:
exceeding 50&nbsp;V&nbsp;ac or 120&nbsp;V ripple-free&nbsp;dc. 
but not exceeding 1000&nbsp;V&nbsp;ac or 1500&nbsp;V&nbsp;dc between conductors, or 600&nbsp;V&nbsp;ac or 900&nbsp;V&nbsp;dc between conductors and earth.

The ripple-free direct current requirement only applies to 120&nbsp;V&nbsp;dc, not to any dc voltage above that. For example, a direct current that is exceeding 1500&nbsp;V&nbsp;dc during voltage fluctuations it is not categorized as low-voltage.

==United States==
In electrical power {{em|distribution}}, the US [[National Electrical Code]] (NEC), NFPA&nbsp;70, article&nbsp;725 (2005), defines '''low distribution system voltage''' (LDSV) as 0&nbsp;to 49&nbsp;V..

The [[National Fire Protection Association|NFPA]] standard&nbsp;79 {{nowrap|article 6.4.1.1}}<ref>{{Cite web|title=NFPA 79: Electrical Standard for Industrial Machinery|url=https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=79|access-date=2021-08-04|website=www.nfpa.org}}</ref> defines ''distribution'' [[Extra-low voltage#Protected extra-low voltage (PELV)|protected extra-low voltage (PELV)]] as nominal voltage of 30&nbsp;V[[Root mean square|rms]] or 60&nbsp;V&nbsp;dc ripple-free for dry locations, and 6&nbsp;Vrms or 15&nbsp;V&nbsp;dc in all other cases.

Standard NFPA 70E, Article 130, 2021 Edition,<ref>{{Cite web|title=NFPA 70E®: Standard for Electrical Safety in the Workplace®|url=https://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=70E|access-date=2021-08-04|website=www.nfpa.org}}</ref> omits energized electrical conductors and circuit parts operating at less than 50 V from its safety requirements of work involving electrical hazards when an electrically safe work condition cannot be established.

[[Underwriters' Laboratories|UL]] standard&nbsp;508A, article&nbsp;43 (table&nbsp;43.1) defines 0&nbsp;to 20&nbsp;V peak&nbsp;/ 5&nbsp;A or 20.1&nbsp;to 42.4&nbsp;V peak&nbsp;/ 100&nbsp;[[Volt-ampere|VA]] as low-voltage limited energy (LVLE) circuits.

==See also==
* [[High voltage]]
* [[Low Voltage Directive]]

==References==
{{Reflist}}

==Further reading==
*[http://electrician2.com/weltrain05/lpage103.html Defining Low Voltage Circuits]

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{{DEFAULTSORT:Low Voltage}}
[[Category:Electrical grid]]
[[Category:Electrical engineering]]
[[Category:Electrical safety]]