said by nunya:De-rating isn't anything new. It doesn't matter what state you are in, the laws of physics still apply. I think it's safe to say that it's been a code requirement for a long time. I would guess over 100 years.
FWIW, going back to 1962 (the earliest I could find) it looks like WI just takes the NEC and adds their own little pre-cursor to the front with some minor amendments.
Basically, it's called the the WI electrical code, but it's really just the same NEC that almost everywhere USA uses.
I should know by now that if I don't properly qualify and source my statements in this forum they will be refuted and rejected. 
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