Mikesh,
T90 and TWN75 are the same thing. At least the T90 that I buy is also marked TWN75. Not that I've tried, but I doubt that you could buy T90 around here that isn't also marked TWN75.
The difference is that when run underground, the cable ampacity is based on 75 degrees C. Which is why I told the OP that he would have to run 3/0.
Can you actually buy T90 in BC that isn't also marked TWN75?
Bruce
