Extra-low voltage (ELV) is an electricity supply voltage and is a part of the Low voltage band in a range which carries a low risk of dangerous electrical shock. There are various standards that define extra-low voltage. The International Electrotechnical Commission (IEC) and the UK IET (BS 7671:2008) define an ELV device or circuit as one in which the electrical potential between two conductors or between an electrical conductor and earth (ground) does not exceed 50V AC or 120V DC (ripple free). The IEC and IET go on to define actual types of extra-low voltage systems, for example separated extra-low voltage (SELV), protected extra-low voltage (PELV), functional extra-low voltage (FELV). These can be supplied using sources including motor / fossil fuel generator sets, transformers, switched PSU's or rechargeable battery. SELV, PELV, FELV, are distinguished by various safety properties, supply characteristics and design voltages. Some types of landscape lighting use SELV / PELV (extra-low voltage) systems. Modern battery operated hand tools fall in the SELV category. In more arduous conditions 25 volts RMS alternating current / 60 volts (ripple-free) direct current can be specified to further reduce hazard. Lower voltage can apply in wet or conductive conditions where there is even greater potential for electric shock. These systems should still fall under the SELV / PELV (ELV) safety specifications. Types Separated or safety extra-low voltage (SELV) IEC defines a SELV system as "an electrical system in which the voltage cannot exceed ELV under normal conditions, and under single-fault conditions, including earth faults in other circuits". It is generally accepted that the acronym: SELV stands for separated extra-low voltage (separated from earth) as defined in installation standards (e.g. BS 7671), though BS EN 60335 refers to it as safety extra-low voltage. A SELV circuit must have: Electrical protective-separation (i.e., double insulation, reinforced insulation or protective screening) from all circuits other than SELV and PELV (i.e., all circuits that might carry higher voltages) Simple separation from other SELV systems, from PELV systems and from earth (ground) The safety of a SELV circuit is provided by The extra-low voltage The low risk of accidental contact with a higher voltage The lack of a return path through earth (ground) that electric current could take in case of contact with a human body The design of a SELV circuit typically involves an isolating transformer, guaranteed minimum distances between conductors and electrical insulation barriers. The electrical connectors