cover required for enclosure containing only low voltage wires?

[malachi constant]

We ran across an existing installation where the covers for VAV control wiring boxes have been lost over time. The enclosures are of varying non-standard sizes and per the contractor covers don't exist off the shelf so would need to be fabricated. Some of the enclosures are in plenum ceilings, we are investigating if the wiring within them is plenum. Assuming we do not have any plenum rating issues, is there a code requirement for the enclosures to be covered? I know for line voltage wiring the answer is yes, but I don't know the answer for control voltage wiring. Thanks!

 

[infinity]

If they're Class 2 then you do not even need a junction box for the splices so I would assume a box without a cover is code compliant.