Adam - I wouldn't do it. Not, at least, before doing
some more research on the particular unit. I recently
found a GE JVT-200 PT. 200:1, 3kVA, two-bushing.
It's positively enormous, as PTs go! Beyond hope, I
actually got an original hardcopy manual with it when
I picked it up. The manual specifically says *NOT* to
ground one HV terminal unless operating at
substantially reduced voltage. I forget the derating
factor. It wasn't something obvious like 1/sqrt(2),
though. It was even worse! I assume this is all
because both sides of the HV are not insulated to 24kV
(or better) from the core.