The supplier or user shall ensure that the factor of safety of every line conductor, including joints, is at least 2.5, which factor shall be based on the rated ultimate tensile strength of the conductor and shall be calculated on the assumption that the line conductor is at a temperature of -5°C and that it is simultaneously subjected to a wind pressure at right angles to the line equivalent to 700 Pa on 0.6 of the projected area of the conductors.