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

The International Electrotechnical Commission defines supply system low voltage as voltage in the range 50 to 1000 V a.c. or 120 to 1500 V d.c..
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.
System voltages around the world are defined in IEC 60038, IEC standard voltages,.

UK

exceeding 50Vac or 120V ripple-free d.c.
but not exceeding 1000 V a.c. or 1500 V d.c. between conductors, or 600 V a.c. or 900 V a.c. between conductors and earth.

USA

In electrical power distribution, the United States National Electrical Code, NFPA 70, 2005, defines low 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 extra-low voltage as nominal voltage of 30 Vrms or 60 VDC ripple free for dry locations and 6 Vrms or 15 V d.c. in all other cases.
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.