(4)The diameter of the drums or sheaves of the winding engine, and of the pulleys and sheaves used in connection with the winding shall, unless otherwise permitted in writing by the Chief Inspector and subject to such conditions as he may specify therein, be not less than eighty times the diameter of the rope in the case of winding installations installed before the 25th day of October, 1955 and not less than one hundred times the diameter of the rope in other cases:Provided that the Chief Inspector may, by an order in writing, require that in the case of any specified winding installation installed before the said date, the diameter of the said drums, pulleys or sheaves shall not be less than such size, as he may specify in the order:Provided further that where special difficulties exist which make compliance with the provisions of this regulation not reasonably practicable, the Chief Inspector may, by an order in writing and subject to such conditions as he may specify therein, relax the said provisions.
