This part EN 50124 deals with insulation coordination in railways. It applies to equipment for use in signalling, rolling stock and fixed installations. Insulation coordination is concerned with the selection, dimensioning and correlation of insulation both within and between items of equipment. In dimensioning insulation, electrical stresses and environmental conditions are taken into account. For the same conditions and stresses these dimensions are the same. An objective of insulation coordination is to avoid unnecessary over dimensioning of insulation. This standard specifies: requirements for clearances and creepage distances for equipment; general requirements for tests pertaining to insulation coordination. The term equipment relates to a section as defined in 3.3 it may apply to a system, a sub-system, an apparatus, a part of an apparatus, or a physical realisation of an equipotential line. This standard does not deal with: distances through solid or liquid insulation; distances through gases other than air; distances through air not at atmospheric pressure; equipment used under extreme conditions. Product standards have to align with this generic standard. However, they may require, with justification, different requirements due to safety and/or reliability reasons, e.g. for signalling, and/or particular operating conditions of the equipment itself, e. g. overhead contact lines which have to comply to EN 50119. This standard also gives provisions for dielectric tests (type tests or routine tests) on equipment (see Annex B). NOTE For safety critical systems, specific requirements are needed. These requirements are given in the product specific signalling standard EN 50129.