MC bundling

[nyerinfl]

Hello gents,

I have been having a recurring problem lately with inspectors on the following scenario: Typical tenant improvement. MC cables run throughout for homeruns and such and such. So say I've got 8 cables running down the hall bundled together with tie wire or what have you. Lately I've been hearing from my inspectors that I need to 'individually tie each cable up' which I think is insane. My view is per 310.15 B (2) ex. 5 I can bundle up to 20 current carriers before I would even have to start any derating. I will be meeting with inspector on Monday, and would like to hear what others think about MC bundling, because I strongly believe I'm right and need to prove this guy wrong.

BTW: The last inspector that tried this sent his chief inspector out who passed it.

 

[scwirenut]

 

[wbalsam1]

IMHO, you're right about excption #5. Go over 20 conductors adjust to 60%.









edited word cables to conductors.

 

[M. D.]

IMO you have it right ,..note; it refers to conductors and not the number of cables

 

[M. D.]

does he like/ trust EC&M magazine ??

http://ecmweb.com/nec/code_top50nec_102607/

Exception 5: The conductor ampacity adjustment factors of Table 310.15(B)(2)(a) do not apply to Type AC or MC cable when:

(1) Each cable has not more than three current-carrying conductors.

(2) The conductors are 12 AWG copper, and

(3) No more than 20 current-carrying conductors (ten 2-wire cables or six 3-wire cables) are bundled.
When 11 or more 2-wire cables or 7 or more 3-wire cables (more than 20 current-carrying conductors) are bundled or stacked for more than 24 in., an ampacity adjustment factor of 60% must be applied.

 

[infinity]

(3) No more than 20 current-carrying conductors (ten 2-wire cables or six 3-wire cables) are bundled.
When 11 or more 2-wire cables or 7 or more 3-wire cables (more than 20 current-carrying conductors) are bundled or stacked for more than 24 in., an ampacity adjustment factor of 60% must be applied.

The use of the wording six 3-wire cables is misleading and in some instances incorrect. For a 120/240 volt single phase system six 3 wire cables would likely be MWBC's and therefore would only count as 12 CCC's not 20.