DC breaker

Midnite Solar has lots of documentation about their breakers:

http://www.midnitesolar.com/products.php?menuItem=products&productCat_ID=16&productCatName=Breakers

And the docs from the OEM:

http://www.midnitesolar.com/pdfs/Q-Series(1).pdf

From what I can tell, it appears that (at least some) breakers can be mounted on a wall, and it does not matter if input is up or down.

HOWEVER, I would highly suggest you contact your reseller (like NAWS, our host @ http://solar-electric.com) directly and ask them (typically, the end retailer is expected to supply first level support).

And if you need further information, ask Midnite directly:

http://www.midnitesolar.com/support.php

I have learned over the years to not guess an answer to questions like these. Circuit breakers have internal arc quench labyrinths, and it is possible that they may be sensitive to mounting (heat rises, and you want to arc to go up the "chute" and not "rise back" into the contacts.

https://electrical-engineering-portal.com/mcb-miniature-circuit-breaker-construction

Even had a major "oops" a few decades ago on mounting disk drives (when they cost $x,000 to $xx,000 each for less than a 500 MByte drive... Fortunately, we asked the manufacturer on wall mounting and which side(s) are up? The manual was not clear. Our local contact went back to the factory/designers and got the "official" answer. A 1/2 year later, we started having a rash of failures and the failure analysis said we installed upside down--But we had the letter from the factory support folks that told us what was acceptable--And the manufacture "ate" the costs (failures and retrofit costs).

-Bill