This standard applies to fuel cell power system installed onboard rolling stock for railway applications (e.g. light rail vehicles, tramways, streetcars, metros, commuter trains, regional trains, high speed trains, locomotives). Fuel cell power systems specified in this standard are used for the traction power and the auxiliary supply of railway vehicles such as hybrid vehicles as defined in IEC 62864-1:2016, and in case of use as an auxiliary onboard power source. This standard applies to the fuel cell technology called PEMFC: Proton Exchange Membrane Fuel Cell, with the use of hydrogen as fuel source and the use of air as oxidant source. This standard is linked to IEC 63341-3 part defined as Railway applications - Hydrogen and Fuel cell systems for rolling stock - Part 3: Performance requirements and tests methods for fuel cell power system . IEC 63341-3 describes the performance test method to validate the FCPS performance. Hydrogen fuel system described in IEC 63341-2 is not considered as a part of the fuel cell power system. Power conversion equipment is described in IEC 61287-1 and will be not considered in this document. This standard focuses on: the scope of supply and the description of the interfaces (fluidic, electrical, thermal and mechanical) of the fuel cell power system, the description of the environmental conditions, the specification and description of all the requirements to ensure the fuel cell power system compliancy with a railway application, the process to validate the fuel cell power system sizing required for a specific load profile, the safety, reliability and protection requirements to design the fuel cell power system for railway application, the marking and labelling requirements, the requirements related to storage, transportation, installation and maintenance, the tests (type, routine and investigation) required to validate the fuel cell power system This standard with the other parts is used in conjunction with other related IEC standards for auxiliary equipment used for railway rolling stock applications.