Insulation resistance equivalencies

[Sean Factotum]

Okay, I'm having a little problem equating two procedures for checking the insulation resistance of a cable. I need to be able to show an equivalent value for these two methods. I swear to Cecil that 10 years ago I could have knocked this out quickly, but that knowledge is gone (because of the "Use It or Lose It" principle.)

Method 1 has a minimum specification of 100 Megohms using 50VDC.
Method 2 has a minimum specification of 0.2 Megohms using 500VDC.

How can I show what the minimum value should be if we used 500VDC instead of 50 in Method 1?

[Sean Factotum]

Here's my one free bump.

I'm thinking of checking the cable in question with a megger at both voltages, just to get a comparison.