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in another Part of the IEC 60439 series of assembly standards not yet transferred into the new IEC 61439 series, the superseded IEC 60439-1 still applies.