Derating of multiconductor "homerun" cable

[JJWalecka]

I was looking at the requirements of 310 regarding bundling of 12/2 mc. But what about mc cable with a four sets of 12 awh. Conductors. Black set, red set, blue set and pink set.

Does that mean no more than six four conductor cables can be in bridal hangers without derating? (4x6=20)


310.15(B)(3)(a)(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.”

 

[Greentagger]

That is a strangely written section. But I would think (b) might determine that we must derate after 3 current carrying conductors. I too would like to see other’s interpretations.

 

[infinity]

Yes, you can bundle up to 20 CCC's in those cables without any adjustment to their ampacity if each cable has 3 CCC's or less.

 

[JJWalecka]

Yes, you can bundle up to 20 CCC's in those cables without any adjustment to their ampacity if each cable has 3 CCC's or less.

But what if the cables have 8 ccc in each cable?

 

[Greentagger]

But what if the cables have 8 ccc in each cable?

Derate?

 

[infinity]

But what if the cables have 8 ccc in each cable?

Then you cannot use the MC cable bundling rule and must use the standard bundling rule based on the total number of CCC's.