Low voltage
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 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 standard IEC 61140:2016, concerning protection against electric shock, defines the low voltage band as ≤ 1000 V AC RMS or ≤ 1500 V DC. This incorporates the Extra-low voltage band.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, but only a minor risk of electric arcs 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, NFPA 70, article 725, defines low distribution system voltage as up to 49 V.The NFPA standard 79 defines distribution protected extra-low voltage 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 defines 0 to 20 V peak / 5 A or 20.1 to 42.4 V peak / 100 VA as low-voltage limited energy circuits.