Frank:
I just read 525.23 (c) and it refers to 525.18 (A) or (B). Well, I can't find 525.18 (A) (B) in my 2002 NEC...
If the 50 amp is for a appliance see 525.23 (B). DEpending on the conditions, and the possible risks involved I probably would install a GFI device for "peace of mind".
Remember, the Code is "minimum requirements", no one can fail for exceeding the Code requirements.

John (HotLine1)

John