IEC 60794-3-12:2012 is a detailed specification for duct and directly buried optical telecommunication cables for use in premises cabling to ensure compatibility with ISO/IEC 11801 and ISO/IEC 24702. Those standards have requirements to ensure that models work for generic cabling and system performances. Values in this standard support these models. This second edition cancels and replaces the first edition published in 2005. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - reference to ISO/IEC 24702; - reference to Fibre B6 (IEC 60793-2-50); - reference to Fibre A1a.3 (IEC 60793-2-10); - reference to the OS2 Fibre as defined by ISO/IEC 11801; - reference to the OM4 Fibre as defined by ISO/IEC 11801. Keywords: buried optical telecommunication cables, ISO/IEC 11801 and ISO/IEC 24702 This publication is to be read in conjunction with IEC 60794-1-1:2011, IEC 60794-1-2:2003 and IEC 60794-3-10:2009.