Would a plastic nail-on device box, used as a junction box, with a blank (flush) plate be a violation of 110.3, if it is installed in an attic or unfinished basement?
If you comply with the box fill requirements, the box is NOT subject to physical damage, has no "unused" openings, and a proper cover, it is compliant with the NEC.
The above is MHO.
John
Redsy, I agree with John. There is nothing prohibiting this installation. I kind of prefer plastic (non conductive) in some situations.
Roger