This standard defines protection principles, describes the railway specific protection functions, defines minimum functional requirements and informative examples of their application, describe technical limits, identify residual risks, describes principles for conformity assessment, for AC and DC electric traction systems. It applies to railways, guided mass transport systems, such as tramways, elevated and underground railways, mountain railways, trolleybus systems, and magnetically levitated systems which use a contact line system. This standard may also be applied to electrified road traffic with contact line, such as truck-trolley systems. This standard applies to new electric traction systems and to all significant changes of existing systems. It does not apply to underground mine traction systems, cranes, transportable platforms and similar transportation equipment on rails, temporary structures (e.g. exhibition structures) in so far as these are not supplied directly or via transformers from the contact line system and are not endangered by the traction power supply system, suspended cable cars, funicular railways, magnetic levitated systems (without contact line system), railways with inductive power supply without contact system, railways with buried contact system that is required to be energized only below the train to ensure safety. This standard does not cover technical requirements for products, rules for maintenance of protection systems.