I was having a discussion with one of my electricians the other day and we came across something i have never seen done, but cant see why it couldnt be done.
existing condition (1) 3" GRC with (3) 500mcm conductors (1) 1/0 ground conductor. we disconnected the 3" conduit from the existing roof top AHU it was going to and run it into a J-box. due to conductor length we spliced the 500mcm in the J-box and run it to a new AHU. my electrician complained about the small bending space in the AHU and said how it would have been nice to have had smaller conductors to work with.
so my question would be: is there are code problem if we would have spliced parallel 3/0 in place of the 500mcm leading from the J-box to the new AHU? I wasnt aware of a vilation to the NEC for doing this, but thought it would be a good question.