In electrical engineering, low voltage is a relative term, the definition varying by context. Different definitions are used in
electric power
Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...
transmission and distribution, compared with electronics design.
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
The
International Electrotechnical Commission
The International Electrotechnical Commission (IEC; ) is an international standards organization that prepares and publishes international standards for all electrical, electronics, electronic and related technologies. IEC standards cover a va ...
(IEC) standard IEC 61140:2016 defines Low voltage as 0 to 1000 V
AC RMS or 0 to 1500 V
DC.
[IEC 61140:2016 Chapter 4.2] Other standards such as IEC 60038 defines ''supply system low voltage'' as voltage in the range 50 to 1000 V AC or 120 to 1500 V DC in ''IEC Standard Voltages'' which defines power distribution system voltages around the world.
In electrical power systems ''low voltage'' most commonly refers to the
mains voltages as used by domestic and light industrial and commercial consumers. "Low voltage" in this context still presents a risk of
electric shock
An electrical injury (electric injury) or electrical shock (electric shock) is damage sustained to the skin or internal organs on direct contact with an electric current.
The injury depends on the Current density, density of the current, tissu ...
, but only a minor risk of
electric arc
An electric arc (or arc discharge) is an electrical breakdown of a gas that produces a prolonged electrical discharge. The electric current, current through a normally Electrical conductance, nonconductive medium such as air produces a plasma ( ...
s through the air.
United Kingdom
British Standard
BS 7671, ''Requirements for Electrical Installations. IET Wiring Regulations'', defines ''supply system low voltage'' as:
The ripple-free direct current requirement only applies to 120 V DC, not to any DC voltage above that. For example, a direct current that is exceeding 1500 V during voltage fluctuations is not categorized as low-voltage.
United States
In electrical power , the US
National Electrical Code
The National Electrical Code (NEC), or NFPA 70, is a regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. It is part of the National Fire Code series published by the National Fire Prote ...
(NEC), NFPA 70, article 725 (2005), defines low distribution system voltage (LDSV) as up to 49 V.
The
NFPA standard 79 defines ''distribution''
protected extra-low voltage (PELV) as nominal voltage of 30 Vrms or 60 V DC ripple-free for dry locations, and 6 Vrms or 15 V DC in all other cases.
Standard NFPA 70E, Article 130, 2021 Edition,
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.
UL standard 508A, article 43 (table 43.1) defines 0 to 20 V peak / 5 A or 20.1 to 42.4 V peak / 100
VA as low-voltage limited energy (LVLE) circuits.
See also
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High voltage
High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant sp ...
*
Low Voltage Directive
References
Further reading
Defining Low Voltage Circuits
{{DEFAULTSORT:Low Voltage
Electricity
Electrical engineering
Electrical safety