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The use of extra low voltage (ELV) in an electrical circuit is one of several means to provide protection 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 Sign warning of possible electric shock hazard An electric shock may occur upon contact with electricity. ...
The International Electrotechnical Commission (IEC) is an international standards organization dealing with electrical, electronic and related technologies. ...
Electrical potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential or the electric potential, typically measured in volts. ...
The term ground (or earth) usually means a common return in circuits. ...
(In IEC terminology, low voltage ranges up to 1000 V AC or 1500 V DC, everything above is high voltage.) Jump to: navigation, search city lights viewed in a motion blurred exposure. ...
Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ...
Three types of extra low voltage sources are distinguished by their safety properties.
Separated Extra Low Voltage (SELV) A Separated Extra Low Voltage (SELV) circuit must be - safely separated from other circuits that carry higher voltages;
- isolated from earth (ground) and from the protective earth conductors of other circuits.
The safety of an SELV circuit is provided by Jump to: navigation, search In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earths conductive surface. ...
- the extra low voltage;
- the low risk of accidental contact with a higher voltage;
- the lack of a return path through earth (ground) that a current could take in case of contact with a human body.
The design of an SELV circuit typically involves an insulation transformer, guaranteed minimum distances between conductors, and insulation barriers. The connectors of SELV circuits should be designed such that they do not mate with connectors commonly used for non-SELV circuits.
A typical example for a SELV circuit is a Class II battery charger. In the electrical appliance manufacturing industry, the following IEC protection classes are used to differentiate between the protective-earth connection requirements of devices. ...
Protected Extra Low Voltage (PELV) In contrast to an SELV circuit, a Protected Extra Low Voltage (PELV) circuit has a protective earth (ground) connection. A PELV circuit, just as with SELV, requires a design that guarantees a low risk of accidental contact with a higher voltage. For a transformer, this can mean that the primary and secondary windings must be separated by an extra insulation barrier or by a conductive shield with a protective earth connection. Jump to: navigation, search In electricity supply systems, an earthing system defines the electrical potential of the conductors relative to that of the Earths conductive surface. ...
A typical example for a PELV circuit is a computer with a Class I power supply. Jump to: navigation, search A computer is a device or machine for processing information from data according to a program — a compiled list of instructions. ...
In the electrical appliance manufacturing industry, the following IEC protection classes are used to differentiate between the protective-earth connection requirements of devices. ...
Functional Extra Low Voltage (FELV) The term Functional Extra Low Voltage (FELV) describes any other extra low voltage circuit that does not fulfill the requirements for an SELV or PELV circuit. Although the FELV part of a circuit uses an extra low voltage, it is not adequately protected from accidental contact with higher voltages in other parts of the circuit. Therefore the protection requirements for the higher voltage have to be applied to the entire circuit.
Examples for FELV circuits include those that generate an extra low voltage through a semiconductor device or a potentiometer.
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