High Working and Test Voltage Specs

Working Voltage and Protective Separation

An important parameter when selecting a suitable isolator or transmitter is the allowable working voltage. It indicates the allowable potential difference between the different circuits (input, output and supply circuits).

llustration of the significance of the working voltage

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. 4800 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.

The specification “protective separation“ always includes the indication of a working voltage up to which the “protective separation“ is guaranteed. All new isolators and transmitters developed by Knick meet the requirements of EN 61140 regarding “protective separation“.

Test Voltage
The dielectric strength of the insulation material used for the isolating components is many times greater than the working voltage permitted for the device. Therefore the test voltage with which each device is tested is specified additionally for potential isolating devices. This ensures that the specified limit values for the working voltage apply to each device.

The test voltage is also used occasionally as a parameter for the dielectric strength instead of the working voltage. This then needs to be a certain factor higher than the maximum possible potential difference between the circuits to be isolated according to the directive for the specific application. The test voltage for Knick isolators is up to 15 kV AC.

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