[Scleros]

I'm installing a wireless access point in a commercial environment on a drop ceiling. The space above the drop ceiling is plenum. The data jack for the access point is installed in an electrical box through a ceiling tile supported by a rod snapped onto the ceiling grid. I want to have the data cable enter the electrical box through a short piece of EMT connected to the box with a compression connector. I've found snap in/on EMT bushings (like Electrical, Fittings, Hubs & Bushings) and threaded ones for use with rigid conduit.

So my questions are:
1. Are these bushings all rated for plenum? How to tell? Where to get?
2. Are the threaded ones only for rigid conduit?
3. Is there a better gizmo for protecting the cable?
4. Does the data jack in the box need to be plenum rated?
5. Do I need to stuff some mineral wool (right stuff?) into the end of the EMT?

[tkrussell]

Very good questions and topic.

Just to be sure we are on the same page, a "plenum" is a space "that acts as part of the air distribution system", as defined by the NEC.

My answers are in bold:

1. Are these bushings all rated for plenum? How to tell? Where to get?
The website you provided is a reseller, not a manufacturer. If made by Arlington Industries, whcih is most likely, then it is rated for plenum space.
See their product information as being compliant with NEC 300.22: B_1

2. Are the threaded ones only for rigid conduit?
No, they can be used on any raceway fitting that is threaded, such as an EMT connector.


3. Is there a better gizmo for protecting the cable?
Not that I am aware of.

4. Does the data jack in the box need to be plenum rated?
Yes, any non-metallic components in an environmental space needs to be be rated for this location. This listing will be found in the manufacturers documentation for their product.

5. Do I need to stuff some mineral wool (right stuff?) into the end of the EMT?
Never use mineral wool. Only use a product that is listed for the purpose, such as Duct-Seal, if necessary. Whether you need to plug yours or not will depend on the AHJ (local inspector) . He may consider how many conduits and their sizes that pass from the plenum to occupied space, and not so much concerned by the affect on the air system but the spread of fire thru these conduits/sleeves

[Scleros]

If made by Arlington Industries, whcih is most likely, then it is rated for plenum space.

I think that website is the retail front for Garvin Industries.

Yes, any non-metallic components in an environmental space needs to be be rated for this location.

The box has a mud ring that extends through the ceiling tile flush with the face of the tile in the occupied space. And the jack would be in the box and part of the occupied space if the interior of the metal electrical box is considered the new "plenum plane"? How is plenum boundary defined?

Never use mineral wool. Only use a product that is listed for the purpose, such as Duct-Seal, if necessary. Whether you need to plug yours or not will depend on the AHJ...

All the communications EMT in the building have what looks like fiberglass insulation stuffed into the ends where they terminate in electrical closets. What does Duct-Seal look like? The stuffing may be for control of heat loss rather than plenum plugging.

[tkrussell]

I could not find any ratings for the Garvin product, you may need to call them to be sure. I would be surprised it was not rated for plenum spaces.

The space stops at the top of the ceiling tile. Since the device is exposed in the occupied space, then there is no problem.

You probably right with the insulation stuffed into the conduit ends. Really not necessary since the space above and below the ceiling is the same air. Duct Seal is a gray putty and is a brand name made by OZ Gedney, many other brands offer something similar. I don't think it is necessary, again, unless something is needed as a fie block, which Duct Seal is not rated, Need to use a fire resistant intumescent putty or caulk.