I have a circuit that is attempting to measure AC line voltage 120-240V but I was told by the certification test lab that my voltage divider resistors would require an expensive 3 week soak test. The resistor voltage divider is behind a 275V varistor to clamp the voltage, a fuse to protect from short circuits and the voltage is being sent through a high linearity 3750V isolation optocoupler biased by a transformerless mains side power supply so I was thinking that the circuit would meet the isolation requirements. Unfortunately, this does not seem to be the case.
Now I am trying to understand what I can do to create a DC bias to power the optocoupler and how to reduce the voltage to be able to send through the optocoupler since a resistive voltage divider does not seem valid without extensive testing. As a result, I need more information and the test lab seems unwilling or unable to provide this. A reference to the relevant standard as well as any suggestions would be appreciated.