Bundling Fire alarm MC with branch circuit MC

[Mustang125]

I understand you can't bundle more than 5 MC together. But I can't find if you are allowed to bundle your fire alarm MC with your regular circuits?

 

[infinity]

There is no 5 cable rule for MC but there are bundling rules for derating power cables that are bundled together or installed on bridal rings.

 

[Ponchik]

You can bundle as many MC cables as you want, however, you need to derate the ampacity of the conductors.

 

[Mustang125]

Your kidding? Haha wow, I have been with my company for 8 years now and we have about 40 guys, and every single person and job I have been to we have never tiewraped more than 5 MCs together, beside derating can you think of a reason? Maybe 5 is the amount before you have to derate? If I remember right, an inspector even made us go above the ceiling in an existing space where all the MCs where entering the electric room, and separate them into groups of 5 or 6 I think.... haha. But don't you have to start derating after 4 current carrying, so 2 MCs together would have to be derated?

 

[Smart $]

Depends on the total number of current-carrying conductors (20)... not the number of cables. I'd say someone made a generalization, to make a visual inspection easier in the field, to cover 310.15(B)(3)(a)(4).

(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.”

Using 12/4 MC copper and 3 CCC's per cable, the cap would be 6. With 4 CCC's per cable, i.e. where the neutral is counted as a CCC, the cap would be 5 cables "bundled" together. There's your magic number.

 

[Smart $]

To answer to your original question 310.15(B)(3)(a) states "Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the adjustment factors shown in Table 310.15(B)(3)(a) shall apply only to the number of power and lighting conductors (Articles 210, 215, 220, and 230)." Fire alarm MC do not contain power and lighting conductors. :happyno:

 

[infinity]

Your kidding? Haha wow, I have been with my company for 8 years now and we have about 40 guys, and every single person and job I have been to we have never tiewraped more than 5 MCs together, beside derating can you think of a reason? Maybe 5 is the amount before you have to derate? If I remember right, an inspector even made us go above the ceiling in an existing space where all the MCs where entering the electric room, and separate them into groups of 5 or 6 I think.... haha. But don't you have to start derating after 4 current carrying, so 2 MCs together would have to be derated?

No not kidding. Saying that 5 cables is the limit is saying that someone doesn't understand how to do the proper calculation. In fact if you look at what Smart posted (#6) for 20 amp circuits/#12 AWG conductors there are instances where there are no limits as to the number of cables that can be bundled.

 

[Strathead]

I understand you can't bundle more than 5 MC together. But I can't find if you are allowed to bundle your fire alarm MC with your regular circuits?

I suspect your original question has to do with the mixing of fire alarm and power MC's If so, then there is no issue from a code perspective.

 

[Mustang125]

Thanks for all the info guys. So basically, you could bundle 10- 12/2 MCs together without derating?

 

[gadfly56]

Thanks for all the info guys. So basically, you could bundle 10- 12/2 MCs together without derating?

Yep. Even more if they are fire alarm cables.

 

[petersonra]

Depends on the total number of current-carrying conductors (20)... not the number of cables. I'd say someone made a generalization, to make a visual inspection easier in the field, to cover 310.15(B)(3)(a)(4).

Using 12/4 MC copper and 3 CCC's per cable, the cap would be 6. With 4 CCC's per cable, i.e. where the neutral is counted as a CCC, the cap would be 5 cables "bundled" together. There's your magic number.

interesting that the cited section does not appear to require all of the stated conditions be true to avoid bundling rules. It appears any of the stated conditions would make it os no derating for bundling was required.

 

[infinity]

Thanks for all the info guys. So basically, you could bundle 10- 12/2 MCs together without derating?

Yes, or any combination of 20 CCC's when there are no more than 3 in any one cable.