The EN 50121 set of standards is designed as a framework for railway EMC management.  The standards specify limits for electromagnetic emission of the railway as a whole to the outside world.  They also set limits for the immunity to electromagnetic emission and immuniy for equipment and rolling stock operating within the railway.

The EMC limits are set so that the railway as a whole satisfies the European Directive on electromagnetic compatibliity with the outside world and so electromagnetic compatibility is achieved within the railway.  It should be noted that the emission limits that are applicable under the European Directive are not necessarily applicable outside the European Union.

The immunity and emision levels that are specified in this series of standards do not guarantee that the railway will be compatible with neighbouring systems or equipment.  In some situations there will be sources of high levels of electromagnetic emissions adjacent to the railway corridor that will require additional measures to be taken by the railway to ensure electromagnetic compatibility.  The standard refers to these as "special locations".

Similarly, the emission and immunity levels specified for equipment and apparatus within the railway are not guaranteed to achieve electromagnetic compatibility.  The specified test levels are usually sufficient to achieve satisfactory results but some locations ("special locations") may require further attention.

The nature of railway systems is such that testing complete systems (complete trains or signalling control centres) is not feasible.  The integration of sub-systemss is asessed on a risk basis and an EMC management plan is used to deal with complex situations or specific circumstances.


The series of Standards EN 50121, Railway applications - Electromagnetic compatibility, contains the following parts:

Part 1: General

This part gives a description of the electromagnetic behaviour of a railway; it specifies the performance criteria for the whole set. A management process to achieve EMC at the interface between the railway infrastructure and trains is referenced.

Part 2: Emission of the whole railway system to the outside world

This part sets the emission limits from the railway to the outside world at radio frequencies. It defines the applied test methods and gives information on typical field strength values at traction and radio frequency (cartography).

Part 3-1: Rolling stock - Train and complete vehicle

This part specifies the emission and immunity requirements for all types of rolling stock. It covers traction stock and trainsets, as well as independent hauled stock.
The scope of this part of the Standard ends at the interface of the stock with its respective energy inputs and outputs.

Part 3-2: Rolling stock - Apparatus

This part applies to emission and immunity aspects of EMC for electrical and electronic apparatus intended for use on railway rolling stock. It is also used as a means of dealing with the impracticality of immunity testing a complete vehicle.

Part 4: Emission and immunity of the signalling and telecommunications apparatus

This part specifies limits for electromagnetic emission and immunity for signalling and telecommunications apparatus installed within a Railway.

Part 5: Emission and immunity of fixed power supply installations and apparatus

This part applies to emission and immunity aspects of EMC for electrical and electronic apparatus and components intended for use in railway fixed installations associated with power supply.

EN 50121-1 and EN 50121-2 are product family standards, which take precedence over generic standards.
EN 50121-3-1, EN 50121-3-2, EN 50121-4 and EN 50121-5 are product standards.

"The enemy of safety is complexity."

 Behind Human Error, Woods et al, Ashgate 2010 p 23

"Knowledge and error flow from the same mental sources, only success can tell one from another."


Ernst Mach, 1905