View source for Protection of a LV generator set and the downstream circuits

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'''Introduction'''

Most industrial and large commercial electrical installations include certain important loads for which a power supply must be maintained, in the event that the utility electrical supply fails: 

*Either, because safety systems are involved (emergency lighting, automatic fire-protection equipment, smoke dispersal fans, alarms and signalization, and so on…) or 
*Because it concerns priority circuits, such as certain equipment, the stoppage of which would entail a loss of production, or the destruction of a machine tool, etc. 

One of the current means of maintaining a supply to the so-called “priority” loads, in the event that other sources fail, is to install a diesel generator set connected, via a change-over switch, to an emergency-power standby switchboard, from which the priority services are fed (see {{FigRef|N1}}).

{{FigImage|DB422640_EN|svg|N1|Example of circuits supplied from a transformer or from an alternator}}