EN 50121-3-2 is Part 3-2 of the European railway electromagnetic compatibility series and specifies the emission limits and immunity requirements that apply to apparatus installed on railway rolling stock. A train generates a demanding electromagnetic environment of its own: the traction converter switches large currents at high frequency, the pantograph loses and regains contact with the overhead line and produces a burst of transient activity each time, and the auxiliary converters and the braking system add further sources, while the vehicle also passes through the fields produced by the signalling and power installations along the route. The standard therefore defines limits for the conducted and radiated disturbance produced by the apparatus and requires immunity to electrostatic discharge, to radio frequency fields, to fast transients and to surges at the levels appropriate to a vehicle installation. It is applied together with the parts of the series that cover the vehicle as a whole, the signalling and telecommunication apparatus and the fixed power supply installations.