ITU-T Recommendations

This Recommendation specifies measures to be taken with respect to safety and risk of damage to equipment through earth potential rise, when power line towers are used for locating radio base stations. It also considers the special lightning protection scheme, which is needed for this type of installation.This is of special concern when power is fed from the low-voltage network, which is the most common situation. Different options are described.Three appendices are attached:Appendix I, titled "Guide on the coordination of the isolation level required for the power supply circuit and the potential rise of power line towers", gives information on how to determine the required isolation voltage level due to the EPR at an earth fault in the tower.In Appendix II, titled "Guide on the LV feeding arrangement", more details on the low-voltage feeding options are given.Finally, Appendix III, titled "Characterization and control of the EPR zone of tower earthing and estimation of the minimum length of the junction section", presents simple calculations for estimation of the EPR for the determination of the length of the so-called junction cable.It also shows graphs of the EPR and touch voltage when grading frame earths around the equipment cabinet are installed.