[sdiy] guessing wire insulation voltage rating

[anthony]

I know this is a query that has the potential (pun intended) for disaster: 
what is a good way of guessing the max voltage rating on a wire's insulation 
if it's not marked? If I can tell it's silicone-based and it's thick, I know 
it's at least good for 1000VDC. But looking at wiring in old tube gear it's 
hard to tell: a lot of it looks pretty puny and it's running 400VDC. Thin 
wire and thick insulation is a good clue that it may be good for tube amp 
voltages. But I guess the thing that makes it confusing is that some wire is 
probably rated with the idea that it's going to have 120VAC or 240VAC 
running through it. I think it's a different ballgame whether it's AC or DC, 
right? I know I could use the old "tickle test" running a varying AC voltage 
from my variac to an old 'scope transformer and holding the wire by its 
insulation while measuring the output of the 1000 volt AC tap (you know the 
one for the 1V2...). But how does the AC rating compare to its DC rating? 
I'm only concerned with running 200-450VDC through the wire. I guess I have 
plenty of wire that is plainly marked, but I have this silver wire insulated 
in what must be Teflon or Teflon-like because it is a bitch to strip the 
"normal" way (but easier if you slide a razor blade up the side...). I like 
it because it's pretty and I think even though the insulation looks thin, 
it's probably rated for something like 600VDC. The guage is pretty heavy for 
high voltage wiring, most of it is 22, but some of it looks like 20 (or 
maybe it's 24 & 22 - being silver makes it look bigger I suppose...).

I know it's better to err on the side of caution. The tickle test only works 
on AC (I THINK) and it's stupid to do on purpose. I do know that brushing 
the 1000VDC part of the scope tube with your finger SUCKS! Not as bad as 
getting a solid jolt from a lawnmower magneto though. No sir. Nuh-uh.

At the very least I could use some of it for filament wiring I guess. Or 
maybe just another low voltage project. One with a panel  that I open up and 
there's the pretty wire...

Thoughts?

cheers,
Anthony