Since when has a High Potential test been in the vicinity of 900V?.
All of the High Potential tests that I've been involved with have been 5000V+.
I think you are confusing a Megger test with a Hi-Pot Test.
Meg-ohm meters use twice the AC RMS voltage as a DC voltage.
For 120VAC this would be 250VDC, for 240VAC this would be 500VDC.
For 400V here in NZ it would be 1000VDC.
Now, I work for a PoCo, company rules state that you MUST be wearing Rubber Gloves and outers before the test starts.
You NEVER muck with HV stuff.
One of our store-men used to be a Line Mechanic, he is missing some of his face and has one finger and a thumb on one hand and two fingers on the other hand.
Cable blew up on a High Potential Test, we get everyone out of the way when we do these tests these days, it was nasty that day.