IEC 62236-4:2018 specifies limits for emission and immunity and provides performance criteria for signalling and telecommunications (S&T) apparatus (including power supply systems belonging to S&T) which may interfere with other apparatus inside the railway environment, or increase the total emissions for the railway environment and so risk causing electromagnetic interference to apparatus outside the railway system. This new edition includes the following significant technical changes with respect to the previous edition: clarification of certain parts of the standard; extension of emission and immunity requirements.