Conduit from above suspended ceiling into panel board without derating

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DPMin

Member
Location
Pennsylvania
This might be an obvious question, and I'm just not creative enough to find a solution!

I need to run about 40 branch circuits (all run with type MC cable) from above a suspended ceiling into a surface mounted panel board. The ceiling is at 12 feet and the top of the panel is at 6 feet, so I have a 6 foot gap to span.

I would love to run just one 2" conduit from a box above the ceiling down into the panel, but since it would be over 24" long I would need to apply a derating factor according to 310.15(B)(3)(a). My next idea was to install a two foot metal trough between two sections of conduit so I could keep them under 24", but as I understand a trough would be considered a "metal wireway" so I would need to apply a derating fator if I had more than 30 current carrying conductors running through it (which I would) (376.22(B)).

I would really like to avoid running 40 three-quarter inch conduits down into the panel (and its a finished room so running the MC straight down isn't an option)...what is the typical solution in a situation like this? I would imagine it would be a common issue (though this is the first time I am dealing with it so may be not...)

Thanks in advance for your help!
 
Buck Parrish

Buck Parrish

Senior Member
Location
NC & IN
Can you run the mc down to the panel then box them in? Build a sheetrock box the same width and depth as the panel all the way up to the cieling.
 
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DPMin

Member
Location
Pennsylvania
hillbilly1 said:
You would only have to derate the wire from the j box down to the panel, you just upsize the wire the proper amount.
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Correct me if I'm wrong, but since I would have over 41 current carrying conductors in the same conduit I would need to use a derating factor of 35. I started out with 12awg, so after derating I would need to use something like 4 awg! :blink:

Buck Parrish said:
Can you run the mc down to the panel then box them in? Build a sheetrock box the same width and depth as the panel all the way up to the cieling.
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masterinbama said:
Why not drop the MC's into the panel and have a sheet metal shop fab a skirt to cover them?
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These are ideas that would certainly make it easier for me, I'll have to talk to the GC and see what he thinks about something like that. Thanks!
 
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suemarkp

Senior Member
Location
Kent, WA
Occupation
Retired Engineer
You don't need a conduit per circuit, you can usually use 9 CCCs into a raceway withotu derating below "normal" if using 90C wire. So 5 conduits should do it, perhaps less if some of these are multiwire branch circuits
 
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hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
DPMin said:
Correct me if I'm wrong, but since I would have over 41 current carrying conductors in the same conduit I would need to use a derating factor of 35. I started out with 12awg, so after derating I would need to use something like 4 awg! :blink:





These are ideas that would certainly make it easier for me, I'll have to talk to the GC and see what he thinks about something like that. Thanks!
Click to expand...

Drop two 2" conduits. Your box would have to be fairly big anyway because of the number of cables coming into it, along with all of the splices.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Take a look at 310.15(A)(2) Exception. If your cable runs are longer than 60', you would not have to derate for the 6' conduit run.
 
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