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 reference [1].
This Recommendation provides a procedure in order to evaluate the expected risk of damages (Rd)
due to direct lightning discharges. If this value is higher than the tolerable risk of damages (RT), then
additional protection measures shall be applied in the telecommunication line in order to reduce Rd.
In accordance with the risk management procedure [1], the difference between the tolerable risk and
the expected risk of damage due to direct flashes (RT - Rd) 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 Recommendation K.46 [2].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 multiplexer, power amplifier, 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 or
customer’s building or remote site). The protection procedures for lines made of optical fibre cables
are given in reference [3].