Abstract: A mobile high voltage network supplies electrical consumer units connected via a plug-in connector and can be switched on and off by means of mechanical switches, with a fuse responding in the event of a short circuit. The high voltage network carries a direct voltage and to each electrical consumer unit (8; 10) a separate diagnostic and protection monitoring system is assigned which is activated when it is switched on and/or off. Such a direct voltage and high voltage network in conjunction with the diagnostic and protection monitoring system makes it possible, before starting up any circuit of consumer units, to effect a self-diagnosis of the protection monitoring system, to ensure that all components are fully functional. Without this, self-diagnosis with proof of functionality the relevant circuit of consumer units is not switched on.