IEC 62855:2016 provides the electrotechnical engineering guidelines for analysis of AC and DC electrical power systems in nuclear power plants (NPPs) in order to demonstrate that the power sources and the distribution systems have the capability for safe operation and shut down of the NPP, bringing it to a controlled state after an anticipated operational occurrence or accident conditions and finally reaching a safe state. This standard is intended to be used: - for verification of the design of new nuclear power plants; - for demonstrating the adequacy and impact of major modifications of electrical power systems in operating nuclear power plants; - and where there is a requirement to assess and establish operating limits and constraints for existing plants.