Can you terminate two conductors under one bolt for a 600 AMP breaker. The conductor size 4/0 and 10 AWG. 
Can you terminate two conductors under one bolt for a 600 AMP breaker. The conductor size 4/0 and 10 AWG.
The terminations where done at the manufacturer
Since that is the case, 90.7 would apply if the equipment is listed as a whole assembly by the manufacturer. If the equipment is listed by an OSHA NRTL, the NEC would not apply to the factory terminations. The NRTL who listed the equipment would of evaluated the terminations for compliance to a ANSI manufacturing standard.
If the equipment is not listed, or only some parts are listed, or are UL recognized components, then the NEC would apply and it would be up to the AHJ to accept and approve the terminations as required in 90.4, 110.2, and 110.3(A)
Now that you point out that the terminations were done at the manufacturer I opened my eyes and saw the manufacturers markings indicating that the bolts have not been disturbed since being torqued at the factory. What that leaves unanswered is Brian's question as to whether the assembly is listed. If it is listed your all set but if not then the listing of the breaker itself or the listing of the lugs if they are add on will determine if the addition of a crimp connector under the bolt head is permissible or not. Unless you have an AHJ who is willing to approve it on the basis of it being a factory assembly. Most would not want to stick their necks out that far and so would demand that you provide a copy of the listing documents.
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Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous for general use." Thomas Alva Edison
Thanks for your help. I pulled the product data off the breaker manufacture website and it says that the beaker is not UL 489 approved for powerpact breakers. They are not available in the US. See attachment. 
After looking at the photo in reality they are terminating 3 conductors you have two 4\0 and a number 10. You have showed documentation for the breaker so it all comes down if it was listed as an assembly?
Parallel 2 runs of #4/0 conductors protected by a 600 amp ocpd is a bigger issue ! #4/0 copper is rated at 230 amp and
aluminum is rated at 180 amp without any "Adjustments"; Also, what is the load for the #10 conductor? The load connected by the #10 conductor IS NOT PROTECTED BY THE 600 amp breaker. Both issues are not NEC code compliant !
Harvey Peel, PE
The cut-sheet states it is not evaluated for use in United States(so if you are in the U.S -no). The parallel 4/o's being protected by a 600A OCPD are a code violation ARTICLE 310,Table 310.6. The jamming under of the 10AWG under the lug would violate the listing of the lug and the torque on it would cause it to burn off . Does not look like any licensed Electrical Inspector should be signing off on that installation.
Pete Delisi ,Electrical Inspector/Plans Examiner.
I think we are looking at too "narrow" a picture. How long are the 4/0's? Do they fall under a tap rule? Are the #10's fused outside the pic frame? If the #10's are attached to a ring lug, then it would be the same as a washer.
And he never did answer whether this is just one area in a larger listed piece of manufactured equipment - that is important.
I have seen things in listed manufactured units that would never fly if done as a field install. I think this is a listed manufactured unit that has not been touched in the field since the bolt head alignment marks are not misaligned.
John R. Maze
110.3(B) and 110.14 would apply to the termination. Is the lug listed for that type of termination? Was the termination made that way by a manufacturer? If it was, is the equipment listed?
My opinion is that the termination was made in the filed and is not legal . The 10 AWG conductors have to be removed and the terminations will have to be re-torqued to their proper values.