What is the relationship between working voltage and isolation rating?

The relationship between a given working voltage and the required test voltage is complex and is a function of the application, the magnitude of common-mode voltage transients (Installation Category), the "cleanliness" of the environment (Pollution Degree), and the required insulation type (Insulation Level). As a representative example based on IEC 1010-1 (international standard for measurement and control equipment), a measurement and control application involving installation category II, a pollution degree of 2, basic insulation, and a working voltage of 300 V_RMS has a required test voltage of 1.35KV_RMS. This means that for an isolation component to be suitable for this application, it must support steady-state common-mode voltages differences of at least 300 V_RMS and transient common-mode voltages differences of at least 1.35KV_RMS. The relationship between working voltage and isolation rating is defined by the specific safety standard for the end-equipment under consideration.