The permitted working voltage of an isolator may differ between the different circuits. The highest of the specified working voltages generally applies across the input and output and across the input and power supply. The permitted working voltage across the output and power supply can be lower. The allowable working voltages for Knick isolators are up to approx. 3600 V AC/DC depending on the model.
The term “protective separation“ is defined in EN 61140. This basic safety standard describes protective measures against electric shocks and thus defines the requirements to be met by electrical isolation between electric circuits. "Protective separation" refers to an isolation system which is characterized by basic protection and additional protection (additional insulation or protective shielding) or by equivalent insulation (reinforced insulation according to EN 61010-1).
It has the aim to protect persons against dangerous body currents. This particularly high level of safety must be ensured by constructive measures (such as appropriate clearance and creepage distances) as well as by the insulation properties of the internal isolation components. That means that the requirements of the basic safety standard have a direct effect on the isolator design.