Switching processes at low and medium electrical loads are experienced forexample in relays and switches for the measuring technology, telecommunications,automotive usage, and appliances. The switching voltage ranges fromμV to 400V with currents between μA and about 100A.

Guided by empirically developed arc-limiting graphs typical switchingprocesses can be distinguished. As Fig. 6.1 illustrates, voltage and currentdetermine if switching occurs without arcing, results in a glow discharge, shortinstable arcs are generated, or a fully developed electrical arc is created. Themore exact current-voltage curve characte-ristics are depending on theelectrical contact material used. They also depend on the contact gap and theatmosphere the switching occurs in; an ambient air atmosphere is assumed inthe shown schematic example.

For the different requirements on the electrical contacts in various applications itis useful to differentiate across the broad spectrum of possible load conditionsguided by the arc-limiting graphs between four different partial ranges which result intypical physical effects:

U < 80mV<br/> I < 10mA<br/>