Why is a suspended ceiling not allowed in a wiring closet?

I have read in the book Cabling: The Complete Guide to Network Wiring that wiring closets should not have a suspended ceiling. In a few Google searches, I see this concept repeated. I have not been able to find a good source on the reasoning of this. Not a "it's up to the local code" kind of reason, but a true explanation of the concepts behind it.

Thanks

Was it posed as a "best practice" thing, or a "law forbids it" thing? You use the term "not allowed" in your title, but you say "wiring closets should not have a suspended ceiling" in your question body.

I have no opinion as to the law (if only because there are far too many jurisdictions for anyone to be able to give you a generic answer), but from a pure practicality point of view, I hate working on wiring in a suspended ceiling, because having to open the roof every time I change a cable is an absolute horror (I've been doing it a bit in our office lately, and it sucks). Give me a space with a snaketray or similar accessable system for running cables any day, thank you very much.

Generally, a drop ceiling implies a plenum, which is the technical term for the space above the drop ceiling. And generally, the plenum is how the air conditioning sucks the air out of the habitable space before heating or cooling it and returning it via ducts and vents.

The actual requirement is that a room dedicated to electrical or communications equipment must have fire stop walls, floors and ceiling rated for 2, 4, or 8 hours depending on some factors. Generally, the easiest way to do that is to make the walls of that room go all the way to the real ceiling.

And once your ceiling is that tall in such a small room, there's no need for a plenum and a drop ceiling is kind of pointless. You can directly vent with ducts and a fire damper to the adjacent plenum.

see cablinginstall.com

Antiquated, mostly a "we've always done it" thing.

Be smart, careful about airflow, don't forget what's up there, no reason you can't.