Specifies dimensional and functional requirements for 'Top Hat' section, 'C' section and 'G' section mounting rails for the compatible mounting of the various electrical devices in switchgear and controlgear assemblies. Appendices cover steel mounting rails in respect of material properties, standard dimensions, manufacturing tolerances and tolerances on form per metre length and an application guide which sets out standard graphical methods of presentation for permissible equipment loading in relation to distance between supports and torsional deflection.