A contractor will pull network cable through the open space above a branch-office ceiling. That space returns air to the air handler and is not a closed metal conduit. Which cable belongs in that space?
Select an answer to reveal the explanation.
Short Explanation
That open ceiling is not just a handy tray. If it carries return air, a burning jacket can feed smoke straight into the air people breathe, so you use plenum-rated cable there. Riser cable is for the vertical path between floors, and a foil shield or a category 6 print does not earn a free pass through an air-handling space.
Full Explanation
A plenum is a space used to move environmental air, such as a ceiling return that is not in a closed duct or conduit. Cable installed there must be plenum-rated so the jacket produces limited smoke if it burns, because the air handler can spread those fumes through the building. That is the rating this branch-office space requires. Riser-rated cable is the usual substitute people reach for. It is intended for vertical runs between floors, and a riser rating does not replace a plenum rating in return air. Ordinary PVC category cable names a performance grade and a jacket compound. Category 6 says nothing about smoke in an air handler, so the category print on the box is the other trap. Shielded twisted pair reduces interference. The foil is not the feature that qualifies a cable for a plenum. Exam caveat: a run inside sealed metal conduit may follow a different local rule than a cable lying in the open return. The stem says the space is not a closed conduit, so the plenum rating applies. Operational check: read the jacket print on the pull and confirm the plenum marking before the ceiling is closed, and keep the cut sheet with the cable map for that closet.