Low voltage
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| 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, when used as an electrical engineering term concerning an electricity supply grid or industrial use, broadly identifies safety considerations of the system based on the voltage used. The meaning of the term "low voltage" is somewhat different when used with regard to a more typical end user's distribution system, which see below.
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[edit] Electricity supply system
With regard to an electricity supply system, 'low voltage' most commonly refers to mains voltage. "Low voltage" in this context is characterized by carrying a substantial risk of electric shock, but only a minor risk of electric arcs through air. Also in this context, "Low voltage" is distinguished from:
- Extra low voltage (supply system) – which carries a much reduced risk of electric shock
- High voltage (supply system) – where electrical arcing is a substantial additional risk.
[edit] Other definitions
Some other commonly used definitions include:
- The International Electrotechnical Commission (IEC) defines low voltage as any voltage in the range 50–1000 V AC or 120–1500 V DC.
- Article 490.2 of the United States 2005 National Electrical Code only defines "high voltage" as more than 600 volts. Nevertheless the NFPA 79 article 6.4.1.1 defines 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 508A article 43.1.2 is more stringent and uses those values as maximum the same way as NEC 2008.
- Within the context of the "distribution system" 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.
- British Standard BS 7671:2008 defines 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.
