Voltage protective extra low

Any voltage above PELV (Protective extra low voltage), i.e. 25V ac or 60V ripple-free dc... 

Where it is not possible to meet all the requirements in subsection 411-02 for SELV, but the voltage does not exceed extra-low voltage, the protection is called protective extra low voltage (PELV). The difference between a SELV and PELV system is that the latter is connected to earth but in other respects meets the SELV requirements. Other extra-low voltage systems are called functional extra-low voltage (FELV). The relevant precautions are detailed in section 471-14. The socket outlets in SELV, PELV and FELV systems... 

Very small transformers are used in electronic applications. Small transformers are used as isolating transformers in shaver sockets and can also be used to supply separated extra-low-voltage (SELV) sources. Equipment supplied from a SELV source may be installed in a bathroom or shower room, provided that it is suitably enclosed and protected from the ingress of moisture. This includes equipment such as water heaters, pumps for showers and whirlpool baths. 

It may be impracticable to supply the more powerful hand tools, such as large angle grinders, at extra-low voltage, so section 606-04-04 allows the use of higher voltage tools protected by electrical separation. As already observed, pneumatic or hydraulically powered tools are an alternative. 

Regulation 608-03-04 requires extraneous conductive parts to be connected to the protective conductor to establish an equipotential zone. The special requirements include the provisions of section 601 if there is a bath or shower, so any socket outlets must be not less than 2.5 m from them. The extra-low voltage (usually 12 V) circuit cables to the rear and brake lights have to be separated from the low voltage wiring see Regulation 608-06-04. 

Therefore a 5 amp fuse or a 6 amp MCB would protect this circuit if ordinary GLS lamps were being used. However, if extra-low voltage or discharge lighting is connected to this circuit and protected by a type B MCB we must take account of the inrush current which occurs at switch-on and sometimes causes unwanted or nuisance tripping of the MCB. To avoid this, the circuit will be adequately protected by a 10 amp MCB. 

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