During our work as electrical safety consultants, we are often asked what level of protection do switchgear doors offer. First of all, it’s important to state the obvious. When switchgear doors are open or covers are removed, there will not be any protection for the worker against either direct contact or internal arcing, other than that afforded by protective equipment such as insulation and barriers, and PPE.
On the otherhand, with doors closed and covers in place, the enclosure will protect against direct contact and may even afford protection against internal arcing. However, the level of protection afforded against the effects of internal arcing is dependent upon the switchgear design and construction, its operation and maintenance, and of course, the magnitude of the arc energy.
For example, low voltage switchgear and controlgear that has been designed and constructed in accordance with IEC I.S.EN 61439-2 Low-voltage switchgear and controlgear assemblies, or its predecessor, IEC EN 60439-1 Low-voltage switchgear and controlgear assemblies – Part 1: Type-tested and partially type-tested assemblies (EN 60439-1 had not been adopted as an Irish Standard by the time it was superseded in 2009), may be said to be designed and constructed in principle to prevent internal arcing when operated and maintained in accordance with the manufacturer’s instructions. However, the risk of internal arcing cannot be disregarded even with such switchgear and controlgear, not to mention those of any other construction.
Crucially, both the IEC I.S.EN 61439-2 and IEC EN 60439-1 Standards contain various requirements that are subject to agreement between the assembly manufacturer and the user, not least of which is short-circuit withstand capability. And so the degree of safety is dependent upon, among other things; the switchgear and controlgear being suitably rated to the operating/prospective operating conditions.
Optional design features such as internal separation and higher degrees of protection such as insulated busbars contribute to reducing the likelihood of arcing, while features such as those for arc detection and rapid extinction, and arc chutes offer protection against injury in the event of internal arcing. And as already stated, the risk of internal arcing is also dependent upon the manner of operation and maintenance of the installation. And so, designers and users of electrical installations have much to ponder.
Finally, only low voltage switchgear and controlgear that has been representatively tested and rated under the prospective conditions of internal arcing in accordance with IEC TR 61641 Enclosed low-voltage switchgear and controlgear assemblies – Guide for testing under conditions of arcing due to internal fault, comes with assurance of its ability to limit to a significant degree the risk of injury due to thermal effects and flying parts and/or shrapnel which result from internal arcing. Even such verified switchgear cannot be expected to afford protection against toxic gas emissions (in the absence of arc chute) or blast noise.
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