IEC 61439-1:2009 lays down the definitions and states the service conditions, construction requirements, technical characteristics and verification requirements for low-voltage switchgear and controlgear assemblies. This standard applies to low-voltage switchgear and controlgear assemblies (ASSEMBLIES) only when required by the relevant ASSEMBLY standard. This first edition of IEC 61439-1 standard cancels and replaces the fourth edition of IEC 60439-1:1999. Significant technical changes with respect to the last edition of IEC 60439-1. IEC 61439-1 is a pure 'general rules' standard to be referred to by subsidiary product parts of the IEC 61439 series; the product standard replacing IEC 60439-1 is IEC 61439-2; the discrimination between type-tested assemblies (TTA) and partially type-tested assemblies (PTTA) is eliminated by the verification approach; three different but equivalent types of verification of requirements are introduced: verification by testing, verification by calculation/measurement, or verification by satisfying design rules; the requirements regarding temperature rise have been clarified; the rated diversity factor (RDF) is covered in more detail; requirements from the standard for empty enclosures for assemblies (IEC 62208) have been incorporated; the whole structure of the standard is aligned with its new function as 'general rules' standard. However, when a dated reference to IEC 60439-1 is made in another Part of the IEC 60439 series of assembly standards not yet transferred into the new IEC 61439 series, the superseded IEC 60439-1 still applies.