Technical Papers: Arc-proof low voltage switchgear and controlgear assemblies

In the last years safety in LV electrical installations has taken an increasingly dominant role.Also from a normative point of view, the panorama has become more complete and a large number of users consider safety in the first place among the necessary requirements for their own plant. 

LV switchgear assemblies are undoubtedly the components of the electric installation more subject to the direct intervention of personnel (operations, maintenance, etc.) and for this reason users demand from them higher and higher safety requirements.

In the last years a lot of users have underlined the question of safety in electrical assemblies with reference to one of the most severe and destructive electrophysical phenomenon: the electric arc.

Unlike tripping devices, for which arc phenomena represents one of the standard operating conditions, in LV switchgear the electrical arc is an absolutely anomalous and rare event. 

But, if the electric arc occurs inside LV switchgear it generates internal overpressures and results in local overheatings which may cause high mechanical and thermal stresses in the equipment.

Besides, the involved materials can generate hot decomposition products, gases or fumes, which, due to the overpressure, are almost always ejected to the outside of the enclosure thus jeopardizing the operator safety.

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The European Directive 2006/95/EC states the fundamental safety requirements for low voltage electric materials (from 50 V to 000 V in alternating current, from 75 V to 500 V in continuos current) to be put on the market within the European Community.

Among the essential safety requirements defined by this Directive particular importance is given to the need of taking technical measures to prevent “temperature rises, electric arcs or radiations which may result in hazards” from occurring.

This aspect has always been highly considered for apparatus, but it has been wrongly neglected for electrical switchgear and only in the last 0-5 years it has been catching on both at Italian as well as at international level.