High, Low and Extra Low Voltage.
The International Electrotechnical Commission and its national counterparts (IET, IEEE, VDE, etc.) define high voltage circuits as those with more than 1000 V for alternating current and at least 1500 V for direct current, and distinguish it from low voltage (50 to 1000 V AC or 120 to 1500 V DC) and extra-low voltage ( below 50 V AC or below 120 V DC) circuits. This is in the context of building wiring and the safety of electrical apparatus.
This is an electrical engineering term that broadly identifies safety considerations of an electricity supply system based on the voltage used. While different definitions exist for the exact voltage range covered by "low voltage", most usually 50 to 1000 V AC, the most commonly used ones include "mains voltage", 230 V AC. "Low voltage" is characterised by carrying a substantial risk of electric shock, but only a minor risk of electric arcs through air. "Low voltage" is distinguished from:
Extra low voltage – which carries a much reduced risk of electric shock
High voltage – where electrical arcing is a substantial additional risk.
This should not be mistaken, by the average person on the street, with commonly understood terms of "Low Voltage Lighting" which in electrical engineering terms actually should be "Extra Low Voltage Lighting" for example.
Extra Low Voltage
In electricity supply, the use of extra-low voltage (ELV) is one of several means to protect against electrical shock. The International Electrotechnical Commission and its member
organizations define an ELV circuit as one in which the electrical potential of any
conductor against earth (ground) is not more than either 25 volts RMS (35 volts peak) for
alternating current, or ripple-free 60 volts for direct current under dry conditions. Lower
numbers apply in wet conditions, or when large contact areas are exposed to contact with the
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements. High voltage is used in electrical power distribution (overhead high voltage cables and pylons for example), in cathode ray tubes, to generate X-rays and particle beams, to demonstrate arcing, for ignition, in photomultiplier tubes, and in high power amplifier vacuum tubes and other industrial and scientific applications.
An Electric Arc
This is when an electrical breakdown of a gas which produces an ongoing plasma discharge, resulting from a current flowing through normally nonconductive media such as air. A synonym is arc discharge. An arc discharge is characterized by a lower voltage than a glow discharge, and relies on thermionic emission of electrons from the electrodes supporting the arc. An archaic term is voltaic arc as used in the phrase "voltaic arc lamp".
Requirements for non-armoured cables with thermosetting insulation of rated voltage up to and including 450/750 V, which produce lower levels of smoke and corrosive gases under exposure to fire, compared with corresponding PVC-insulated cables specified in BS 6004.
British Standard BS 7671 "Requirements for electrical installations" is the national standard in the United Kingdom for low voltage electrical installations. For more click here.
The 17th edition, released in January 2008, is the latest edition of BS7671, and became effective for all installations designed after 1 July 2008. One of the more significant changes is (chapter 41) that 30 mA RCD's will be required for socket outlets that are for use by ordinary persons and are intended for general use. This improves the level of protection against electrical shock in the UK to a level comparable to that in other EU countries. The 17th edition incorporates new sections relating to microgeneration and solar photovoltaic
The IET (Institution of Engineering and Technology) is one of the world's leading professional societies for the engineering and technology community, with more than 150,000 members in 127 countries and offices in Europe, North America and Asia-Pacific. The IET provides a global knowledge network to facilitate the exchange of ideas and promote the positive role of science, engineering and technology in the world. For more click here.
The Institution of Electrical Engineers (I.E.E.) was a British professional organisation of electronics, electrical, manufacturing, and Information Technology professionals, especially electrical engineers.
The I.E.E. was founded in 1871 as the Society of Telegraph Engineers, changed its name in 1880 to the Society of Telegraph Engineers and Electricians and changed it again to the Institution of Electrical Engineers in 1889.
It was Incorporated by a Royal Charter in 1921.
In 2006, the I.E.E. merged with the Institution of Incorporated Engineers (I.I.E.) to form the Institution of Engineering and Technology (I.E.T.). Before the merger, the I.E.E. was the largest professional engineering society in Europe, with a worldwide membership of around 120,000 For more click here.
IEC (International Electrotechnical Commission)
The IEC is the international organization for the preparation of safety standards and other standards in the area of electrical engineering. International orientation on the focus of its activities is a stated objective of electrotechnical standardization. Considerably more than 50 % of the production of the German electrotechnical industry is exported - international standardization is, therefore, a basis for economic success.
CENELEC (European Committee for Electrotechnical Standardization)
CENELEC is involved with the
conversion of IEC standardization results into European Standards; almost 85 % of the European Standards are based on IEC work results or are identical with them. In addition,
CENELEC prepares its own European Standards - focused on European requirements. Furthermore, CENELEC has the task to establish a link between standardization and legislation - for the benefit of consumers and industry.
For more click here.
ETSI (European Telecommunications Standards Institute)
The ETSI is responsible for the preparation of standards for an integrated European telecommunications infrastructure; this also includes subjects of related areas, such as radiocommunication and information technology.