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, and 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
| IEC voltage range | AC RMS voltage (V) |
DC voltage (V) | Defining risk |
|---|---|---|---|
| High voltage | > 1 000 | > 1 500 | Electrical arcing |
| Low voltage | 50 to 1 000 | 120 to 1 500 | Electrical shock |
| Extra-low voltage | < 50 | < 120 | Low risk |
The International Electrotechnical Commission (IEC) defines supply system low voltage as voltage in the range 50 to 1000 V AC or 120 to 1500 V DC.
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.
UK
- British Standard BS 7671:2018 defines supply system low voltage as:
exceeding 50Vac or 120V ripple-free dc but not exceeding 1000Vac or 1500Vdc between conductors, or 600Vac or 900Vac between conductors and Earth
(note the ripple free direct current requirement only applies to 120Vdc it does not apply to any direct current voltage above that. For example if you have ripple direct current that is exceeding 1500Vdc during voltage fluctuations it is not categorized as low voltage)
USA
In electrical power distribution, the United States 2005 National Electrical Code (NEC) defines low (distribution system) voltage as 0 to 49 volts. Low distribution system voltage is covered by Article 725 of this code.
The NFPA standard 79 article 6.4.1.1 defines distribution protected extralow voltage (PELV) as nominal voltage of 30 Vrms or 60 VDC ripple free for dry locations and 6 Vrms or 15 VDC in all other cases.
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 circuits.