I couldn't find in section 408 that talkes about breakers on the left are odd numbered and the breakers on the right are even numbered. Is this a code requirement?

I installed a subpanel from SQUARE-D that had the option of being installed with the Main lugs down or up. So I installed it the way that was convenient for the existing wiring and the existing feeder. Then when i installed the cover the upper left breaker was #12, upper right breaker was #11.

408.3(E) is phase arrangement only, i didn't see anything in 240 or 404. the only issue i find is with 110.3(B) which i should be O.K.

Is this a violation of NEC?

Not a violation. There isn't even anything that says you have to number the circuits, you could use letters or make up a bunch of symbols. I've even seen the left side numbered 1 - 22 and the right side 23 - 42.

Most resi panels have 'numbers' stamped into the deadfront (cover), and a factory directory on the door, or on the cover. The directory should 'match' the factory numbers, or the directory should match the breaker ID that you install.

The only NEC Article is 110.3 (b).

No.

As you said, the panel is designed that way.

I think it comes from English being read left to right and top to bottom.
I would think that panels in Japan and Israel would be numbered differently since they read somewhat differently than most of us on this forum are used to.

Ghost307,
That is a good point. i never thought about it that way.

Thank you all for your comments.

Most, but not all panels are listed for mounting in either direction. Check before you do. As for the numbering method, that is a industry standard, not a code requirement. I can not quote you the origin though. Panels use to be numbered starting on the left going down then continued on the right. If there was two or three pole breaker in the mix, that counted only as one circuit.

Square D' I-Line panel has no numbering on the trim/dead front at all.