How do I run ENT to an old work box?

Question

I have an existing low-voltage old-work box similar to this which I am using to provide a cable TV outlet:

I would like to run more cables to this location, namely, phone and CAT6. I do have access to the location behind the wall through the attic. However, I would like to improve this by drilling a hole through the floor into the basement where all the cables come into the house anyway, and pushing ENT through the hole and attaching it to something different in this location (this box does not have ENT connections).

The only way I know of to make this work is to rip out drywall to expose the entire cavity between the studs, install a new-work low-voltage box to one of the studs, and replace and patch the section of drywall:

I am certainly capable of doing this and have done similar tasks in the past, but would rather avoid the extra work if possible.

One thing I have done in other locations is to push ENT into the wall cavity and get it close enough to the outlet location that when I fish cable though, it is possible to grab it through the hole with fingers or pliers. However, this particular wall cavity has the chimney stack behind it with extra room (much deeper than a 2x4 stud cavity), so cables have too much room to wiggle around and there is a risk they will be too far behind the wall to reach and pull through the outlet box. If I can somehow do the difficult task of grabbing ENT once, and get it attached to a box, then future work will be trivially easy.

Is there a way to securely attach ENT to a box in this location without removing any drywall?

This particular project is restricted to low-voltage work and does not involve real electrical. Location is the USA with no known building codes out of the ordinary that are relevant to this project.

Answer 1

Just use a metal old-work box, perfectly fine for low-voltage stuff. It will have standard knock-outs for conduit connection, as opposed to PVC boxes which commonly have spring-lever grabbers for NM sheathed cable:

Answer 2

1. Drill the hole in the basement into the wall
2. Push your ENT up to the opening after you remove the box.
3. Put a connector on your ENT if you haven't already.
4. Here is the trick, insert a bent piece of tie wire or a bent coat hanger into the ENT.
5. Put you low voltage box over the wire and insert it into the wall.
6. Pull on the wire to bring the connector up into the box.
7. Once the connector is in the box pull hard on the wire to remove it.

Usually this trick works better with steel flex and a locknut but it can be done with ENT.

Good luck!

Answer 3

I think you will find it much easier to push a fish tape through the hole than trying to fish the ENT directly.

It's probably going to be easier to push the fish tape through the hole from the outlet side, where you hit the hole by controlling the tape, rather than by pushing the tape up from the basement and trying to grab it inside the wall.

Either way, once you have the fish tape in place, you can either attach the end of the ENT in a traditional manner and pull it through, or slide the ENT over the end of the fish tape and push it through the hole using the stiff tape as a guide.

If you don't have a fish tape, you can try using just about any stiff wire or tubing. I have fished short distances such as you describe with a 10/2 romex, 75ohm coax, and the plastic tubing that delivers water to my refrigerator. The principle is to trace out the path with something stiffer and more controllable than ENT, Cat5E, etc.