This Recommendation contains the calculation procedure for the shielding factors used in ITU T K.46, ITU-T K.47, ITU-T K.56, and ITU-T K.94, and it is intended to: i. provide the rationale for the shielding factor approximate formulas or values contained in the aforementioned Recommendations; ii. allow a more precise calculation of the shielding factors, by using the equations provided in this Recommendation. The shielding factors considered in this Recommendation refer to: " The lightning current distribution in a telecommunication tower, i.e., the tower factor (?T) as per ITU T K.56 and ITU-T K.97. " The lightning current distribution among several conductors placed in a cable ladder, i.e., the feeder factor (?F) as per ITU T K.56 and ITU-T K.97. " The shielding factor (?) provided by cable trays, as per ITU T K.56. " The guard wire shielding factor (?) as per ITU T K.47. " The refraction factor (?) due to the earthing connection of a telecommunication cable, as per ITU T K.46. " The shielding factor (?) provided by a telecommunication cable having a metallic sheath (shield), as per ITU T K.46.