This European Standard applies to signalling and telecommunication apparatus that is installed inside the railway environment. Signalling and telecommunication apparatus mounted in vehicles is covered by EN 50121-3-2:2016, signalling and telecommunication apparatus installed inside the substation and connected to substation equipment is covered by EN 50121-5:2016. This European Standard 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 Electro-Magnetic Interference (EMI) to apparatus outside the railway system. The requirements specified in this standard apply for: — vital equipment such as interlocking or command and control; — apparatus inside the 3 m zone; — ports of apparatus inside the 10 m zone with connection inside the 3 m zone; — ports of apparatus inside the 10 m zone with cable length > 30 m. Other apparatus not covered by at least one of these given cases should be in compliance with EN 61000-6-2. If a port is intended to transmit or receive for the purpose of radio communication (intentional radiators, e.g. transponder systems), then the radiated emission requirement in this standard are not intended to be applicable to the intentional transmission from a radio-transmitter as defined by the ITU. Immunity limits do not apply in the exclusion bands as defined in the corresponding EMC related standard for radio equipment. The standard does not specify basic personal safety requirements for apparatus such as protection against electric shock, unsafe operation, insulation co-ordination and related dielectric tests. The requirements were developed for and are applicable to this set of apparatus when operating under normal conditions. Fault conditions of the apparatus have not been taken into account. The frequency range considered is from DC to 400 GHz. No measurements need to be performed at frequencies where no requirement is specified. For products in the scope of EN 61000-3-2, EN 61000-3-3, EN 61000-3-11 or EN 61000-3-12 the requirements of those standards also apply. These specific provisions are to be used in conjunction with the general provisions in EN 50121-1:2016. The immunity and emission levels do not of themselves guarantee that the integration of apparatus will necessarily be satisfactory. The standard cannot cover all the possible configurations of the apparatus, but the test levels are sufficient to achieve satisfactory EMC in the majority of cases.