The actual voltage can be tested with a high value resistor and DMM. They work like a zena diode at there stated voltage plus a safety margin.
I would use a regulated HT power supply monitored with an accurate DMM and another DMM connected in series with the junction under test.
Subtract the readings and you have the actual reading ready to de-rate with your safety margin.
I would use a regulated HT power supply monitored with an accurate DMM and another DMM connected in series with the junction under test.
Subtract the readings and you have the actual reading ready to de-rate with your safety margin.
