Division .1 Exposed metal parts of electrical machines or equipment which are not intended to be live but which are liable under fault conditions to become live shall be earthed unless the machines or equipment are:F1

supplied at a voltage not exceeding 50 V direct current or 50 V, root mean square, between conductors; auto-transformers shall not be used for the purpose of achieving this voltage; or

supplied at a voltage not exceeding 250 V by safety isolating transformers supplying only one consuming device; or

constructed in accordance with the principle of double insulation.