Section 64(4) in The Indian Electricity Rules, 1956
(4)The "Highest System Voltage" is defined as the highest rms phase to phase voltage which occurs under normal operating conditions at any time and at any point of the system. It excludes voltage transients (such as those due to system switching) and temporary voltage variations due to abnormal system conditions (such as those due to fault conditions or the sudden disconnection of large loads).](b)[ The windings of motors or other apparatus within reach from any position in which a person may require to be, shall be suitably protected so as to prevent danger. [Substituted by G.S.R. 843, dated 23.7.1985 (w.e.f. 7.9.1985). ](c)Where transformer or transformers are used, suitable provision shall be made, either by connecting with earth a point of the circuit at the lower voltage or otherwise, to guard against danger by reason of the said circuit becoming accidentally charged above its normal voltage by leakage from or contact with the circuit at the higher voltage.(d)A sub-station or a switch-station with apparatus having more than 2000 litres of oil shall not [* * *][be located in the basement where proper oil draining arrangement cannot be provided. [Substituted by G.S.R. 843, dated 23.7.1985 (w.e.f. 7.9.1985). ](e)Where a sub-station or a switch-station with apparatus having more than 2000 litres of oil is installed, whether indoor or out-doors, the following measures shall be taken, namely:-(i)The baffle walls [of 4 hour fire rating][shall be provided between the apparatus in the following cases:- [Substituted by G.S.R. 843, dated 23.7.1985 (w.e.f. 7.9.1985). ](A)single phase banks in the switch-yards of generating stations and sub-stations;(B)on the consumer premises;(C)where adequate clearance between the units is not available.(ii)Provisions shall be made for suitable oil soakpit and where use of more than 9000 litres of oil in any one oil tank, receptacle or chamber is involved, provision shall be made for the draining away or removal of any oil which may leak or escape from the tanks, receptacles or chambers containing the same, special precautions shall be taken to prevent the spread of any fire resulting from the ignition of the oil from any cause and adequate provision shall be made for extinguishing any fire which may occur. Spare oil shall not be stored in any such sub-station or switch-station.(iii)[ All the transformers and switchgears shall be maintained in accordance with the maintenance schedule given in the relevant Code of Practices of BIS and the authorised person shall keep a record thereof as required under rule 3(6).(iv)Notwithstanding anything contained in rule 64(2)(d) and rule 64(2)(f)(ii), only dry type of transformers shall be used for installations inside the residential/commercial buildings.](f)[(i) Without prejudice to the above measures, adequate fire protection arrangement shall be provided for quenching the fire in the apparatus; [Substituted by G.S.R. 358, dated 30.4.1987 (w.e.f. 9.5.1987). ](ii)Where it is necessary to locate the sub-station/switch-station in the basement following measures shall be taken:-(a)The room shall necessarily be in the first basement at the periphery of the basement;(b)The entrances to the room shall be provided with fire resisting doors of 2-hour fire rating. A curb (sill) of a suitable height shall be provided at the entrance in order to prevent the flow of oil from a ruptured transformer into other parts of the basement. Direct access to the transformer room shall be provided from outside.(c)[ The transformers shall be protected by an automatic high velocity water spray system or by carbon dioxide or BCF (bromochloro-difluromethane) or BTM (bromotrifluromethane) fixed installation system or nitrogen injection and drain method.](iii)[ Oil-filled transformers installed indoors shall not be on any floor above the ground or below the first basement.] [Substituted by G.S.R. 358, dated 30.4.1987 (w.e.f. 9.5.1987). ](g)Cable trenches inside the sub-stations and switch-stations containing cables shall be filled with sand, pebbles or similar non-inflammable materials or completely covered with non-inflammable slabs.(h)Unless the conditions are such that all the conductors and apparatus may be made dead at the same time for the purpose of cleaning or for other work, the said conductors and apparatus shall be so arranged that these may be made dead in sections, and that work on any such section may be carried out by an authorised person without danger.(i)Only persons authorised under sub-rule (1) of rule 3, shall carry out the work on live lines and apparatus.]
