Recommendation ITU-T K.46 gives a procedure to protect telecommunication lines using metallic symmetric conductors (i.e., twisted pair cables) against overvoltages and overcurrents imposed on the lines due to nearby lightning flashes. The procedure is based on the representation of the line by a sequence of sections and nodes, and the evaluation of each node exposure to the lightning-induced surges. Based on the node exposure, the ground flash density and the earth resistivity, the annual number of surges above a given voltage level is calculated. If the voltage level considered is the impulse withstand voltage of the node, then the number of surges above this level corresponds to the annual number of damages to the node. This number shall be multiplied by the loss due to induced surges in order to obtain the risk of failure due to indirect lightning flashes. The highest risk of all nodes is the risk of the line.