Voltage safety extra low

Some people assume that the term low voltage means safe voltages, but as you have seen the LVD applies to products that operate at typical line (mains) voltages (e.g., 230/400 volts in Europe and 120/208 volts in the U.S.) that present shock and fire hazards. Safe voltages are those less than 50 Vac/60 Vdc, depending on the standard or term applied and are referred to as Extra-Low Voltage or Safety Extra-Low Voltage (ELV/SELV). 

Tbere are occasions when even a 110 V supply from a centre-tapped transformer is too high for example, supplies to inspection lamps for use inside damp or confined places. In these circumstances a safety extra-low voltage (SELV) supply would be required. 

Fig. 16.2 Welding under a walkway in a ship s engine room. The safety precautions are (1) The power source is fitted with a low voltage device. (2) The handlamp and heated quiver are fred from step-down transformers and operate at safety extra-low voltage. (3) There is an insulated box for the electrode holder when not in use. (4) The fumes are extracted by the centrifugal fan. (5) The operator is wearing insulated clothing and rubber boots and is separated from the steel floor by l5nng on dry wooden planks. (6) There is a second person present.

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