(1) The load and permissible stresses on the structural members, conductors and earth wire of self supporting steel lattice towers or steel monopole towers for overhead transmission lines shall be as per relevant standards.
(2) Overhead lines not covered in sub-regulation (1) shall have the minimum factors of safety as per the table given below:- Description Minimum factor of safety metal supports 1.5 mechanically processed concrete supports 2.0 hand-moulded concrete supports 2.5 wood supports 3.0
(3) The minimum factor of safety shall be based on such load as may cause failure of the support to perform its function, assuming that the foundation and other components of the structure are intact.
(4) The load shall be equivalent to the yield point stress or the modulus of rupture, as the case may be, for supports subject to bending and vertical loads and the crippling load for supports used as strut.
(5) The strength of the supports of the overhead lines in the direction of the line shall not be less than one-fourth of the strength required in the direction transverse to the line.
(6) The minimum factor of safety for stay-wires, guard-wires or bearer-wires shall be 2.5 based on the ultimate tensile strength of the wire.
(7) The tension limit for conductor and earth wire shall be as per relevant standards.
(8) For the purpose of calculating the factors of safety in sub-regulation (2), the following conditions shall be observed, namely: –
(i) the maximum wind pressure shall be as specified in the relevant standards;
(ii) for cylindrical bodies the effective area shall be taken as full projected area exposed to wind pressure;
and
(iii) the maximum and minimum temperatures shall be as specified in the relevant standards.
(9) Notwithstanding anything contained in sub-regulation (2) to (8), in localities where overhead lines are likely to accumulate ice or snow, the load and permissible stresses on the structural members, conductors and earth wire of self supporting steel lattice towers and steel monopole towers for overhead transmission lines shall be as per relevant standards and in accordance with the specifications laid down, from time to time, by the Appropriate Government by order in writing.