Low voltage installations for low voltage devices. Where it's used? For example, in bathrooms or showers. Let's see them: 
<ul><li>SELV or safety extra-low voltage - 12V with timer or 24V with overheating protection. In real life you also can see 12V transformers with overload protection in low-voltage halogen lamps.</li>
<li>FELV or functional extra-low voltage - 36V with overload protection and ground wire. During Soviet times it was widely used in filling stations, in Europe it is used in industrial objects with hazards.</li>
<li>PELV or protected extra-low voltage - voltage up to 48V, where one pole is grounded. Overload protection is used only near loads or other line longer than 3 meters.</li></ul>
All of them should have different sockets, which will allow to use devices only with related low voltage system.
<a href="//commons.wikimedia.org/wiki/User:Dmitry_G" title="User:Dmitry G">Dmitry G</a>
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