scope:

This Recommendation gives a procedure in order to protect telecommunication lines using metallic symmetric conductors against overvoltages and overcurrents imposed on the lines due to nearby lightning discharges.

The procedure is based on the evaluation of the conventional length. Once an upper limit for the conventional length has been selected, this procedure allows the selection of appropriate protection measures to be adopted to reduce the conventional length at or below the tolerable limit.

This Recommendation follows the risk management procedures as described in [ITU-T K.72]; the risk assessment is limited to the failure of insulation of telecommunication lines (buried or aerial cables, shielded or unshielded cables) which can cause the loss of service.

In accordance with the risk management procedure [ITU-T K.72], the difference between the tolerable risk (R_T) and the expected risk of damage due to direct flashes (R_d) is the tolerable risk (R_T-R_d) for the expected risk of damage due to flashes near a telecommunication line.

The user shall refer to [ITU-T K.47] for evaluating the expected risk of damage due to direct lightning discharges, either to the line itself or to the structures where the line enters, and, if necessary, in order to select the protection measures to reduce the risk of damage due to direct flashes.

The protection needs 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 electronic site).

NOTE - Information on line and environment characteristics should be given to the owner of the structure connected to the telecommunication line, who has to perform the risk assessment of his structure (see also Appendix III).

The protection of persons using telecommunication equipment inside the exchange or the customer's structure, from dangerous situations caused by touch voltages, is outside the scope of this Recommendation and it should be evaluated using the risk assessment applied to the exchange or the customer's structure.