scope:

The scope of this Recommendation is the protection of telecommunication lines using metallic conductors against direct lightning discharges to the line itself or to the structures that the line enters. When applying this Recommendation, the user shall follow the risk management procedure, as described in [ITU-T K.72].

This Recommendation provides a procedure in order to evaluate the expected risk of damage (R_d) due to direct lightning discharges. If this value is higher than the tolerable risk of damages (R_T), then additional protection measures shall be applied in the telecommunication line in order to reduce R_d.

In accordance with the risk management procedure [ITU-T K.72], the difference between the tolerable risk and the expected risk of damage due to direct flashes (R_T - R_d) constitutes the tolerable risk for the expected risk of damage due to flashes near a telecommunication line. The latter is evaluated following the procedure reported in [ITU-T K.46]. Lines made from the following types of cables are covered by this Recommendation:

- symmetric cable: Cable with a metallic sheath and a core made of one or many metallic symmetric copper pairs, with or without a plastic covering and/or a supporting wire;

- coaxial cable: Cable with metallic inner and outer conductors separated by a dielectric, with or without a plastic covering and/or a supporting wire.

The protection need of line equipment (such as multiplexers, power amplifiers, optical network units) and line termination equipment is not considered by this Recommendation and it should be evaluated using the risk assessment applied to the structure where the equipment is located (i.e., exchange, customer's building or remote site). The protection procedures for lines made of optical fibre cables are given in [ITU-T K.25].