NM in cable tray

-=PEAKABOO=-

Senior Member
I have a large resi job that I would like to use cable tray to cross and area of the basement to land all of the romex at the panels.
The panels are surface mounted on a concrete wall. My plan was to fabricate metal covers the same size as the panel 3.5" deep, 14" wide, 26" tall, basically a 3 sided box to hide or protect the romex. I am not sure if this will require derating the wire because it may be considered a raceway.


The other question I have.
I have read until I am blue in the face and I am still not sure I know the proper answer.
It is involving fill, derating etc of NM in a cable tray.
I believe I have calculated the fill correctly but wanted some second opinions before I make the move.
The whole time I was looking at doing this I kept seeing that thread of the cable tray full of romex that was posted here a while back.

Where it gets confusing is 392.9.
Not sure what size cable tray I would need and how much if any derating would be involved.

cable tray calc erased.jpg

Thanks
 

defears

Senior Member
Location
NJ
Derating with NM sucks. Not worth it. Get a bunch of 2X10's and nail then up and staple the NM straight. Looks nicer too. Just paint the plywood above the panels black and call it a day.

I think you're over thinking this.:D
 

-=PEAKABOO=-

Senior Member
Derating with NM sucks. Not worth it. Get a bunch of 2X10's and nail then up and staple the NM straight. Looks nicer too. Just paint the plywood above the panels black and call it a day.

I think you're over thinking this.:D
I agree on over thinking it. The GC and the home owner want this and money is not an issue with this guy. I am preparing just in case I cannot easily talk him out of it.
 

kwired

Electron manager
Location
NE Nebraska
Probably cost less to install raceways to cross what ever area they want to cross with the cable tray. Put a junction box(es) at the other end and then run NM cable from there. 3 or 4 runs of 3/4 can carry most of the circuits in an average house - especially if MWBC's are used, AFCI has made this more of a problem though.
 

-=PEAKABOO=-

Senior Member
Probably cost less to install raceways to cross what ever area they want to cross with the cable tray. Put a junction box(es) at the other end and then run NM cable from there. 3 or 4 runs of 3/4 can carry most of the circuits in an average house - especially if MWBC's are used, AFCI has made this more of a problem though.
Again cost is not an issue. It is more of a cosmetic decision, no ceiling can go in because and air handler that was installed. I originally planned on doing this in EMT/thhn and feeding large junction boxes or gutters and making joints but the thought of over 440 joints (listed above) and that does not include the lighting had me thinking cable tray might be an option. There is no attics and we were very limited on where could set panels. I will go read the other thread some more and try to understand this a little better, makes my eyes hurt:cool:
 

kwired

Electron manager
Location
NE Nebraska
Again cost is not an issue. It is more of a cosmetic decision, no ceiling can go in because and air handler that was installed. I originally planned on doing this in EMT/thhn and feeding large junction boxes or gutters and making joints but the thought of over 440 joints (listed above) and that does not include the lighting had me thinking cable tray might be an option. There is no attics and we were very limited on where could set panels. I will go read the other thread some more and try to understand this a little better, makes my eyes hurt:cool:
Not trying to talk you out of the tray, but I would put terminal strip in junction box as well as equipment grounding bar(s) I only come up with about 290 joints, plus equipment grounding conductors. You would not need to run a separate EGC for every cable through the raceway(s) just terminate them at the junction box and run 1 back to the panel (maybe 1 per raceway). That said you will still spend enough time making it all up that it may be worth considering the tray. I am not familiar enough with tray, but deration is probably an issue here, especially with a closed tray, an open type tray may not be if cables are secured and spaced correctly.
 

-=PEAKABOO=-

Senior Member
Not trying to talk you out of the tray, but I would put terminal strip in junction box as well as equipment grounding bar(s) I only come up with about 290 joints, plus equipment grounding conductors. You would not need to run a separate EGC for every cable through the raceway(s) just terminate them at the junction box and run 1 back to the panel (maybe 1 per raceway). That said you will still spend enough time making it all up that it may be worth considering the tray. I am not familiar enough with tray, but deration is probably an issue here, especially with a closed tray, an open type tray may not be if cables are secured and spaced correctly.
Cable tray, if used would be the open, ladder type tray. Considered conduits to junction boxes which was the original plan, the home owner would actually prefer this but cable tray seemed like a simple solution. The lighting is still up in the air, I am 90% sure they are going to use a panelized lighting system like crestron or lutron but I am still waiting on answers about this. They have a lighting design company that did the lighting layout and a home owner that cannot make up his mind about what brand or type of lighting control he wants, anyday we should have an answer.
 

kwired

Electron manager
Location
NE Nebraska
Cable tray, if used would be the open, ladder type tray. Considered conduits to junction boxes which was the original plan, the home owner would actually prefer this but cable tray seemed like a simple solution. The lighting is still up in the air, I am 90% sure they are going to use a panelized lighting system like crestron or lutron but I am still waiting on answers about this. They have a lighting design company that did the lighting layout and a home owner that cannot make up his mind about what brand or type of lighting control he wants, anyday we should have an answer.
With open cable tray time you saved making all the junctions is (at least partially) consumed with making all the cables nice and neat in the tray, you still have considerations as far as which is better/easier/least cost, that may not be all that easily made, and will likely come down to personal preference in the end.
 

-=PEAKABOO=-

Senior Member
After reading the link recommended I feel more confused:dunce:
Will the romex I listed above legally fit in a 24" ladder type cable tray and if so will I need to derate?

Thanks in advance.
 

rbalex

Moderator
Staff member
NM is permitted in Tray [Table 392.3(A)]

With ladder tray you install the Cables per 392.9(A) generally. Since all the conductors are less than #4/0 then 392.9(A)(2) & Table 392.9, Column 1 specifically. Assuming the cross sectional area of the conductors is correctly computed to be 12 sq in. A 24” tray permits 28 sq in.fill.

Note: In the “other thread,” Don pointed out that Chapter 9, Table 1, note (9) does not apply to cable trays. I agree, but I don’t know of any other way to determine the proper cross sectional area of the NM.

Their ampacity is determined by 392.11(A). If they are a random lay, the ampacity is determined by 392.11(A)(1); basically, Table 310.16 and no derating. If they have a maintained spacing not less than one cable diameter, the ampacity is determined by 392.11(A)(3).

In any case, the ultimate ampacity is still limited to the applicable 60?C rating.
 
Last edited:

-=PEAKABOO=-

Senior Member
NM is permitted in Tray [Table 392.3(A)]

With ladder tray you install the Cables per 392.9(A) generally. Since all the conductors are less than #4/0 then 392.9(A)(2) & Table 392.9, Column 1 specifically. Assuming the cross sectional area of the conductors is correctly computed to be 12 sq in. A 24? tray permits 28 sq in.fill.

Note: In the ?other thread,? Don pointed out that Chapter 9, Table 1, note (9) does not apply to cable trays. I agree, but I don?t know of any other way to determine the proper cross sectional area of the NM.

Their ampacity is determined by 392.11(A). If they are a random lay, the ampacity is determined by 392.11(A)(1); basically, Table 310.16 and no derating. If they have a maintained spacing not less than one cable diameter, the ampacity is determined by 392.11(A)(3).

In any case, the ultimate ampacity is still limited to the applicable 60?C rating.

Thanks a million, this makes it a lot easier to understand.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
...
Note: In the ?other thread,? Don pointed out that Chapter 9, Table 1, note (9) does not apply to cable trays. I agree, but I don?t know of any other way to determine the proper cross sectional area of the NM. ...
Bob,
Why would you not just use the published dimensions and multiply them? Even if you apply note 9, you would have to start with the published dimensions.
 

rbalex

Moderator
Staff member
As I mentioned, I didn?t know where the ODs came from so I did ?quick calc? as I believe it should be done.

I didn?t know where the spread sheet from the OP came from either; however, the ?quick calc? led to some interesting numbers.

It appears that the ?Total Sum of the Diameters? from the OP(18.06') is actually the approximate sum of the cross sectional areas. Compare the column 6 [Sum of OD (in)] from the OP to Column 6 [Sum X Area] from my calc. The real Total Sum of the Diameters is about 56?.

It also appears whoever did the OP spreadsheet thought the method I used to determine the effective cross sectional area of the NM only used the major diameter.

The actual sum of the cross sectional areas is still around 18sq in so it will ?fit? in a 24? cable tray. Since a ?random lay? is the only possible installation, 392.11(A)(1) applies.

Tray_Page_1.jpg
 

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