This Recommendation gives a procedure to protect telecommunication lines using metallic components against direct lightning flashes to the line itself or to the structures that the line enters. Lines made by the following types of cables are covered by this Recommendation: Symmetric cable: Cable with a core made of one or many metallic symmetric pairs, which may have a metallic sheath, and/or a plastic covering, and/or a supporting wire; Coaxial cable: Cable with metallic inner and outer conductors separated by a dielectric, which may have a plastic covering and/or a supporting wire; Optical fibre cable: Cable with optical fibres, which may also have metallic components such as an inner strength member and/or an outer metallic sheath.