Gambicas Controlgear Group Technical committee has welcomed the long-awaited publication of IEC 61439, the new series of international standards for low-voltage switchgear and controlgear assemblies, which will soon be implemented in the UK as BS EN 61439.
The organisation warns, however, that manufacturers working to the new standard will need to exercise a high level of skill and caution in relation to the ratings they adopt for components used in their assemblies.
The root concern is that the nominal current rating of components relates to tests carried out in ‘free air’. For these tests, the component is mounted on an open framework with air space all around it, which helps to dissipate excess heat.
These test conditions are very different from the conditions in which the component will operate when installed in an assembly, and as a result, substantial de-rating may be needed to ensure safe operation and to comply with the temperature rise requirements of IEC 61439. In effect, nominal component ratings should be considered only as a starting point for making sound engineering decisions.
Further information and guidance on component ratings is available as a free download from the Gambica website.