Supporting Conductors in Vertical Raceways (300.19)

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WiresMakeMeNuts

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Location
Virginia
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Electrical Contractor
This is my first post on ANY forum, EVER, but I have often lurked on this forum and others to help research code issues, etc. So thank you for the wealth of knowledge that I've gleaned over the years. I apologize in advance if I am not following the protocols...

A little background: I am an electrical contractor. The subject project is currently being designed and I am intimately involved from a constructability perspective, but will also likely be responsible for building the project after the design is complete.

This project will have a vertical raceway embedded in concrete for 250-300'. Naturally, the conductors in this raceway will need to be supported per 300.19 at the intervals in table 300.19 (A). The conductors are branch circuits, likely #12 to #4 in size (still under design...). Believe it or not, but I have essentially the same problem on another very similar project...

I haven't run into this before, but 300.19 (C) offers four options to support the conductors. I don't think options (1), (2), or (3) will work, since there is no access to the conduit for the entire run, being that it is embedded in concrete. We've considered relocating the conduit so that it is exposed or installing embedded junction boxes, but that is not ideal from my perspective or the client's, for a variety of reasons.

This leaves option (4) under 300.19(C)(4) "Other Approved Means." :).

I can't imagine that I am the first person to run into this problem, but I am struggling to find a product or solution for this. The best thing I've come up with is installing a messenger cable in the conduit and supporting the conductors on the messenger (or maybe some type of tri/quatraplexed cable). I don't see anything in Article 396 precluding this, but messenger supported cable is typically horizontal and not in conduit...

So here are my questions:
1. Are there manufactured solutions/products out there that would solve this problem? That would be my preferred solution...
2. Has anyone ran into this before and what was the solution?
3. Does anyone have any experience using a messenger supported or tri/quadraplexed cable in vertical conduit as I explained above? If so, would that work in this application? What did you use to attached the cable to the messenger as I'm not sure typical lashing will work?
 
WiresMakeMeNuts said:
I can't imagine that I am the first person to run into this problem, but I am struggling to find a product or solution for this. The best thing I've come up with is installing a messenger cable in the conduit and supporting the conductors on the messenger (or maybe some type of tri/quatraplexed cable). I don't see anything in Article 396 precluding this, but messenger supported cable is typically horizontal and not in conduit...
Click to expand...
I don't see how this would work so from what I'm reading this is not an option. You would need to find a cable assembly that is designed to be supported solely at the top of the run, if someone actually makes one. That would eliminate the need to have support points within the vertical run of conduit.
 
infinity said:
I don't see how this would work so from what I'm reading this is not an option. You would need to find a cable assembly that is designed to be supported solely at the top of the run, if someone actually makes one. That would eliminate the need to have support points within the vertical run of conduit.
Click to expand...
Thanks for your response. I agree in the case of a tri/quatraplexed cable, it would need to be manufactured for that purpose. Also agree that it is unlikely that I will find something, although I haven't quite given up.

However, I don't think messenger supported wiring (Article 396) would need to be specially manufactured for this. Of course, the messenger itself and its attachment would need to be capable of supporting the full load from the top, but that should not be a problem.

Here's why I think this would be permitted from a code perspective:
  1. 396.10(A) permits MC, SE, UF, TC, among others, to be installed on messenger.
  2. 396.10(B) permits any conductor type from Table 310.4(1) (IE THHN, XHHW, RHW, etc.), IF in an industrial establishment where only serviced by qualified people.
  3. 396.30(A) requires that the tension on the conductors be eliminated.
  4. Either 396(A) or (B) could apply to my projects in question.
  5. In the case of 396.10(A), using MC cable as an example (but some of the other options would also work for me), I would need to follow 330.30 and secure it to the messenger every 6', as well as 396.30(A) and prevent tension on the conductors.
  6. In the case of 396.10(B), I'm not aware of any specific interval to secure the conductors, so I just need to follow 396.30(A) and prevent tension on the conductors.
Again, I definitely prefer a manufactured solution, I just haven't found anything... DEFINATELY open to other ideas, this was just the best I could come up with...
 
Just an outside guess here, but I bet the companies that manufacture travelling electrical cables for elevators could make a suitable cable. It don't think the normal travelling cables would be suitable for NEC applications in a conduit, since these are more like flexible cords not building wire, but I bet they know how to attach thhn to a messenger that could hang in a conduit.

Consider: https://www.jamesmonroewire.com/wp-content/uploads/2018/07/elevator-cable_brochure-Rev6.pdf
 
I was on a similar electrical installation years ago for a fire pump and to maintain 2” of concrete the conduit was encased in a cmu wall with the required pull boxes for support. After the pull was completed we chocked everything and installed, I think 3m fire stop sheets.

The sheets were about 3/8 thick and we fire caulked the edges. And secured the sheets with masonry anchors.
 
I don't see a problem with using a messenger cable to support the wire, especially if cable grips were used at correct intervals. Of course, the AHJ would have to approve it. That's where the "other approved means" comes in.

It might also be worth a call to a company that makes aerial cables, like Okonite. Although like you said, messenger cables are usually horizontal, and free air, it's possible they have been down this road before.
 
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