A guy was talking about some lonwork transformer being above the t-grid having to be plenum rated.

I thought a plenum was a duct or airway. What kinds of things have to be plenum rated and is above the t grid in an office a plenum?

I also remember a guy talking about have tie wraps used above the t grid had to be plenum rated. I'm not familar with this.

Basically, everything has to be plenum rated if its in a plenum ceiling.

Look at 300.22(C).
Don

Panduit makes Plenum rated tie wraps

Sometimes the space above a drop ceiling is used as the return air plenum. If so, everything in the ceiling has to be plenum rated. Sometimes the space below a floor or in a wall can be used this way too.