Electricity shall not be transmitted into a belowground mine at a voltage exceeding 11000 V and shall not be used therein at a voltage exceeding 6600 V:
Provided that, -
(i) where hand-held portable apparatus is used, the voltage shall not exceed 125 V;
(ii) where electric lighting is used, –
(a) in belowground mines, the lighting system shall have a mid or neutral point connected with earth and the voltage shall not exceed 125 V between phases;
(b) on the surface of a mine or in an open cast mine or oil mines or oil-fields, the voltage may be raised to 250 V, if the neutral or the mid-point of the system is connected with earth and the voltage between the phases does not exceed 250 V;
(iii) where portable hand-lamps are used in belowground mines and hazardous area of oil mines or oil-fields, the voltage shall not exceed 30 V;
(iv) where any circuit is used for the remote control or electric inter-locking of apparatus, the circuit voltage shall not exceed 30 V for below ground mine or hazardous area of oil-fields:
Provided that in hazardous areas of oil mines or oil-fields, the said voltage can be up to 250 V, if the onoff control push-button stations or remote controls are housed in an appropriate enclosure like:
(i) Flame proof enclosure type „d‟;
(ii) Pressurised enclosure type „p‟;
(iii) Sand filled apparatus type „q‟;
(iv) Increased safety enclosure type „e‟, „n‟, and „o‟:
Provided further that the control circuit shall have suitable protection against shock hazards, and the trippings due to faults do not adversely affect the operational safety:
Provided also that in fixed plants on surface of the mines or opencast mines, the said voltage for the remote control or electric inter-locking may be permitted up to 250 V.