12/4 MC Bundling

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Diddle720

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So we are doing a TI project and for the original wiring they have 24x24 Jboxes with MC coming out to the different rooms/areas. Each Jbox has around 20+ MCs most are 12/4 so 3 circuits and 1 neutral obviously. My question is on the bundling of MC. I know its 20 current carrying conductors but doesn't that also state that it limits it to 3 current carrying conductors per cable before derating?

Any help and code articles is much appreciated.
 
You could have 12/4 mc and still only have 3 current carrying conductor. Also I don't see anywhere in the article 310.15 that states the mc cables must be limited to 3 ccc.

Individually you may have to de rate if there are 4 current carrying conductor but that does not usually affect the ampacity since we derate from the 90C column
 
Im assuming your feeding from a 3ph. 120/208 Y system then 310.15 B5b would be your code and all four conductors of the MC are considered current carrying. I may be off on this more knowledgable hands will tell.
 
FREEBALL said:
Im assuming your feeding from a 3ph. 120/208 Y system then 310.15 B5b would be your code and all four conductors of the MC are considered current carrying. I may be off on this more knowledgable hands will tell.
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He said 12/4 with 3 circuits (assuming A/B/C), 1 neutral. Neutral would not be counted as CCC unless more than 50% non-linear load.
 
Basically you're allowed up to 20 CCC without the need to apply derating when the conductors are #12, there are no more than 3 CCC's in a single cable and the cable is not PVC jacketed. If you exceed 20 CCC's then a 60% adjustment factor applies. The two specific "exceptions" that apply to bundling AC and MC cables are 310.15(B)(3),(4)&(5):

310.15(B)(3)(4) Adjustment factors shall not apply to Type AC cable
or to Type MC cable under the following conditions:
a. The cables do not have an overall outer jacket.
b. Each cable has not more than three current-carrying
conductors.
c. The conductors are 12 AWG copper.
d. Not more than 20 current-carrying conductors are
installed without maintaining spacing, are stacked, or are
supported on ?bridle rings.?
(5) An adjustment factor of 60 percent shall be applied
to Type AC cable or Type MC cable under the following
conditions:
a. The cables do not have an overall outer jacket.
b. The number of current carrying conductors exceeds 20.
c. The cables are stacked or bundled longer that
600 mm (24 in) without spacing being maintained.
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