Safety Voltage (Extra Low Voltage)
Voltage which does not exceed 50 V a.c. r.m.s. between conductors, or between any conductor and earth, in a circuit isolated from the supply by means such as a safety isolating transformer, or converter with separate windings; a voltage which does not exceed 50 V d.c. between conductors, or between any conductor and earth, in a circuit which is isolated from higher voltage circuits.
NOTE 1 Consideration should be given to the use of equipment operating at less than 50 V under certain conditions, such as wet surroundings, exposure to heavy seas or powerful water jets where direct contact with live parts is involved.
NOTE 2 The voltage limit should not be exceeded either at full load or no-load but it is assumed, for the purpose of this definition, that any transformer or converter is operated at its rated supply voltage.
Source: IEC 61892-6, Mobile and fixed offshore units – Electrical installations – Part 6: Installation. Global Standards