Correct option is B
The load permissible stresses on the structural members, conductors and ground wire of self-supporting steel lattice towers for overhead transmission lines shall be in accordance with the specifications laid down, from time to time, by the Bureau of Indian Standards.
Overhead lines shall have the following minimum factors of safety:
for metal supports - 1.5
for mechanically processed concrete supports - 2.0
for hand molded concrete supports - 2.5
for wood supports - 3.0
Minimum factors of safety:
The minimum factors of safety shall be based on such load as may cause failure of the supports to perform its function.
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 struts.
The strength of the supports of the overhead lines in the direction of the line shall not less than one-fourth of the strength required in the direction transverse to the line.
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.
The minimum factor of safety for conductors shall be 2, based on their ultimate tensile strength.
