|IEC voltage range||AC||DC||defining risk|
|High voltage (supply system)||> 1000 Vrms||> 1500 V||electrical arcing|
|Low voltage (supply system)||50–1000 Vrms||120–1500 V||electrical shock|
|Extra-low voltage (supply system)||< 50 Vrms||< 120 V||low risk|
Low voltage is a relative term, the definition varying by context. Different definitions are used in electric power transmission and distribution, and in the electronics industry. Electrical safety codes define "low voltage" circuits that are exempt from the protection required at higher voltages. These definitions vary by country and specific code.
Electrical power supply industry definitions
In the electrical power supply industry, 'low voltage' most commonly refers to mains voltage or power transmission lines. "Low voltage" in this context still presents a risk of electric shock, but only a minor risk of electric arcs through the air.
- British Standard BS 7671:2008 defines supply system low voltage as:
- 50–1000 V AC or 120–1500 V ripple-free DC between conductors;
- 50–600 V AC or 120–900 V ripple-free DC between conductors and Earth.
Electrical power distribution industry definitions
In the context of electrical power distribution, the United States 2005 National Electrical Code (NEC) defines low (distribution system) voltage as 0 - 49 volts. Low Distribution (system voltage) is covered by 250.20(A) of this code.
The NFPA standard 79 article 22.214.171.124 defines distribution 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.
Electronics design and manufacturing industry definition
UL standard 508A article 43 (Table 43.1) defines 0-20V peak/ 5A or 20.1-42.4V peak/ 100VA as Low-Voltage Limited Energy circuits.