(1) In the interest of safety, the earth fault current shall not be more than 750 milliampere in installations of voltage exceeding 250 V and up to 1100 V for below ground mines and oil-fields, and 50 ampere in installations of voltage exceeding 1100 V and up to 11 kV in open cast mines and the magnitude of the earth fault current shall be limited to these specified values by employing suitably designed, restricted neutral system of power supply including neutral-ground monitoring protection system:
Provided that all electrical installations, in or after notification of these regulations, of voltage exceeding 1100 V and up to 11 kV for below ground mines, open cast mines and oil mines or oil-fields, the magnitude of the earth fault current shall be limited up to 10 A by employing suitably designed, restricted neutral system of 136 THE GAZETTE OF INDIA : EXTRAORDINARY [PART III—SEC.4] power supply including neutral-ground monitoring protection system:
Provided further that the settings of protective relays thereof shall be set between 200 to 400 milliampere for individual apparatus of voltage up to 1100 V with suitable time delay protection.
(2) The operation of the switchgear and the relays shall be recorded daily at the generating station, substation or switch station in a register kept for the purpose and in electronic form also.
(3) The effectiveness of switchgear and protective system shall always be kept in working order and shall be checked by calibrating and testing at least once in a year and the result thereof shall be recorded in separate register kept for the purpose and in electronic form:
Provided that wherever numerical relays are being used they shall be checked by testing procedure as per guidelines of original equipment manufacturer or the relevant standards and periodicity of such checking shall be at least once in a year.