The title should be enough of a question to get an answer, but in case it's more nuanced here's some details and the particular finding that made me ask.
Searching online for an NEC definition of "suspended ceiling" has got me nowhere.
A large portion of my basement has a surface mount grid system with your bog standard accoustical/fire retardant panels. The strips with the channels that the tile-supporting strips snap into are mounted directly to the joists, so when a panel is installed there is anywhere from 0" to 1/4" of space available for a panel to be lifted. Here is an actual image from my basement showing how it looks:
I have already asked a question about whether or not the stapled NM is a violation here, and there are other violations elsewhere that I know I have to resolve such as cable not being secured within 12" of a box, and low voltage being run through the same bores as mains. So needless to say, anywhere that a cable/wire is running over this ceiling I will be pulling the panels down to correct everything I can.
Why I'm here today:
There is a junction box that I finally came across inside this ceiling. It is mounted properly, but it is of course completely hidden by the panels when they're installed. It is my understanding that this is acceptable for a suspended ceiling. Given that generally a panel can be removed individually with minimal effort/damage the code makes some sense.
However, the surface mount system is the exact opposite. You usually cannot remove just one panel. And you can't remove any without first removing some of the grid pieces. This process also usually damages the panels because they require an unsettling amount of force to remove them. That puts the ease of access closer to drywall than a suspended ceiling.
I also have similar concerns for the junction box as I do for the stapled NM cables. The proximity of the junction box to the essentially fixed panels puts it within striking distance of things that could penetrate the ceiling; either accidentally or intentionally.
I understand that code is the minimum that we have to meet and that there's nothing stopping me from putting an access cover on the ceiling panel, but I want to have a better understanding of what changes I have to make vs the ones I want to make.