These guidelines relate to the activities to plan and perform to maintain the characteristics of overhead contact lines at the levels expected to guarantee the performance required for the relevant railway lines. This IRS sets out guidelines to ensure the best maintenance of all overhead railway contact lines (OCL) fed both in DC or in AC current, under different traffic conditions, speeds, etc. The leaflet can be applied in particular to maintain OCL systems operating at the following voltages: 1.5 kV and 3 kV DC, 15 kV - 16 2/3 Hz, 25 kV - 50 Hz.