Warm welcome for new standard plus a warning

GAMBICA'S Controlgear Group Technical committee has welcomed publication of IEC 61439, a new series of international standards for low-voltage switchgear and controlgear assemblies, which will be implemented in the UK as BS EN 61439. GAMBICA warns, however, that manufacturers working to the new standard still need to exercise skill and caution in relation to the ratings they adopt for components used in their assemblies.

The nominal current rating of circuit breakers and other components relate to tests carried out in 'free air'.

The component is mounted on an open framework with air space all around it, which helps to dissipate excess heat, very different from the conditions in which the component will operate. As a result, substantial derating may be needed to ensure safe operation and to comply with the temperature rise requirements of IEC 61439. Nominal component ratings should be considered only as a starting point for making sound engineering decisions on PSC design and construction.

Reputable manufacturers will be aware of these issues, and will willingly undertake testing to determine ratings that are appropriate to the use of particular components in their enclosure systems. Alternatively, the manufacturers may choose to adopt another approach permitted by IEC 61439, which relies on calculations that incorporate generous safety margins.