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 FprEN 50121 3 2, signalling and telecommunication apparatus installed inside substation and connected to substation equipment is covered by FprEN 50121 5. 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. Apparatus which complies with the emission levels of EN 61000 6 4 will meet the emission requirements of this standard provided that emissions from any DC power port are within the emissions limits specified for AC power ports. The immunity levels given in this standard apply for - vital equipment such as interlocking or command and control, - apparatus inside 3 m zone, - ports of apparatus inside 10 m zone with connection inside 3 m zone, - ports of apparatus inside 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. The immunity levels given for the apparatus will in most cases allow the apparatus to perform as intended inside the railway environment. The immunity level establishes a common reference for evaluating the performance of the apparatus when subject to interference resulting from direct exposure of the apparatus and associated cables to a radio frequency field, or by coupling of the interference from a remote source. If a port is intended to transmit or receive for the purpose of radio communication (intentional radiators, e.g. transponder systems), then the radiated emis ...