Cable Tray Rating Conductors

[majesus]

I am curious about the "Cable Tray (CT) Rating” in accordance with the NEC.

What peaked my curiosity about this rating is when I was looking at a mining application for a portable 30m conveyor. The conveyor requires 5kV flexible cable for its power feed.
The CT rating was required because the cable was going into a cable tray alongside the conveyor. However you won't find a flexible, 3 conductor mining cable (with ground check) @ MV that is CT rated and MSHA approved. How come? You would think that a cable used for portable equipment such as trailing cable for shovels, draglines, etc, would be built way more robust than a cable that you place in cable tray for protection?

Also on a side note, why aren't most power MV cables CT rated until you get above 1/0AWG?
The best article I could find on cable tray rating is this:

http://www.cabletrays.com/techbl16.pdf.

It states, the cable tray rating tests for: "flammability and other mechanical (including a crush test) and temperature tests" that allow them to be marked cable tray rated." However, aren't many cables that don’t have the rating, tested in similar fashion? The article didn’t describe why most MV cables aren’t CT rated until you get buy larger than 1/0AWG diameter conductors.

 

[dpc]

The #1/0 size issue comes about because NEC Article 392 sets #1/0 as the minimum size for single-conductor cables.

Are you talking about "TC" cable?

Anyway, Type MV cable can be run in tray. See 392.3. You do have to follow the #1/0 size restrictions for single conductors.

Check out Article 392 for more info. There are all kinds of things that can be run in cable tray in addition to TC cable.

 

[BJC]

Does the NEC apply to portable mining equipment? I don't think the NEC is a problem, check chapter 1, verse 1.
I have used cable tray for type SO, SJO etc. It is more rugged than many types and sizes of tray cable. The trick was never to put "Cable tray" on the drawing. Refer to it as "cable support". An inspector suggested that to me once. He knew that the SO was more rugged and better sited to the application but couldn't find a code section to justify it in cable tray. Cable tray is a type of "continuous rigid cable support"

 

[majesus]

Thanks guys for the info.

Interesting that you can have a MV multiconductor smaller than 1/0 in a cable tray, but you can't have a single conductor MV cable in a cable tray that is smaller than 1/0. FMI (for my info) why is that? (If anyone cares to explain it.)

Great tip on Cable Support vs Cable tray. Still curious what defines Cable Tray Rated, as opposed to something like Type SO? Which was suggested as rugged, yet doesn't have the CT rating.


I find it interesting that you aren't able to get a 3 conductor cable (with ground check) @ MV that is CT rated and MSHA approved.

 

[dpc]

If you have an MV cable, the NEC allows it to be run in tray. I have no idea about MSHA rules.

The reason for the size restriction is to keep the cable from sagging below the rungs of ladder tray. A 3/C #1/0 multi-conductor cable is going to be a lot stiffer than a single conductor #1/0 cable.

 

[majesus]

Ah... interesting I went back looking for Cable tray rated on multiconductors in the NEC and all Found was 392.3(B)(1)(a):
Single-conductor cable shall be 1/0 AWG or larger and shall be of a type listed and marked on the surface for use in cable trays.

392.3(B)(2): MEDIUM VOLTAGE. Single and multiconductor medium voltage cables shall be Type MV cable. Single conductors shall be installed in accordance with 392.3(B)(1).

Nothing about multiconductors having to be CT rated.

However, in the CSA:
Rule 12-2202 Conductors in Cable Trays (see Appendix B)
(1) Conductors for use in cable trays shall be listed in Table 19 and, except as permitted in Subrules (2) and (3), shall have a continuous metal sheath or interlocking armour.

On a side note: as for the reason for the size restriction is to keep the cable from sagging below the rungs of ladder tray. What is you take on a 14 AWG 2 conductor cable, it should be more stiff? (I'm just in on the learn process.)

 

[dpc]

It might not be stiffer, but it is a lot lighter.

I'm not familiar with CSA, but with the NEC, you do have to be careful since most section of the NEC apply to low voltage only and there are special sections to cover medium-voltage applications.

Also, there comes a point when trying to apply logic to the Code doesn't really help you. It is what it is -- even if it makes no sense.

 

[majesus]

"Also, there comes a point when trying to apply logic to the Code doesn't really help you. It is what it is -- even if it makes no sense."

TRUE.