MC cable bundled together

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NYC Elect

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I see in 310.15, not more than 20 ccc can be bundled together without it being derated. Can someon explain what this means to me...On my job I see 15 12/3 MC cables being bundled together for about 30'...Is this a legal installation?
 
mc cable bundled together

mc cable bundled together

Yes,... If the overcurrent protective devices are sized properly.

I'm assuming these are mutiwire branch circuits containing two ungrounded conductors and a common neutral

I'm also assuming these circuits are supplying receptacles for cord and plug connected loads.

A 60 percent adjustment factor shall be applied where the current carrying conductors in these cables that are stacked and bundled longer than 24" without maintaining spacing exceeds 20.

60 percent of 30 amps is 18 amps

240.4 (b) (1) states you cannot go to the next higher standard overcurrent device rating when the conductors being protected are part of a multioultet branch circuit supplying receptacles for cord and plug connected portable loads.

I would accept 15 amp overcurrent protective devices for this installation.


Joe Villani
Electrical Contractor
Junior Inspector
 
As Joe said for multi receptacle circuits these would need to be derated to a 15 amps. Depending on the supply system (i.e.-208Y/120) your 15-12/3 cables could contain 45 current carrying conductors. That would require a derating factor of 35%. This means that for 20 amp circuits supplying multiple receptacles you would need to run a minimum of 6/3 cables.
 
Rule 310.15 Exemption (5) (2) also says that if the conductors are 12 awg copper this rule does not apply...So in my case, if I have 12/3 MC, do I even have to worry about the derating factor?
 
mc cable bundled together

mc cable bundled together

Yes

Continue to read exception # 5

#3 states that not more than 20 current carrying conductors are bundled, stacked, or supported on "bridle rings"

With 15 12/3 mc cables I am calculating at least 30 current carrying conductors so exception #5 (3) woulld not apply.

Continue reading the exception and at the bottom it states a 60 percent adjustment factor shall be applied where the current carrying conductors in theses cables that are stacked or bundled longer than 24 inches without maintaining spacing exceeds 20

So in this case a 60 percent adjustment factor will apply.

I have a question,

Can an inspector in NYC even see this? I thought that there is no open wall or ceiling inspections, only finals.
 
NYC Elect said:
Rule 310.15 Exemption (5) (2) also says that if the conductors are 12 awg copper this rule does not apply...So in my case, if I have 12/3 MC, do I even have to worry about the derating factor?
Click to expand...
Exception No. 5 to 310.15(B)(2)(a) is ALL inclusive.


Exception No. 5:
Adjustment factors shall not apply to Type AC cable or to Type MC cable without an overall outer jacket under the following conditions:
(1) Each cable has not more than three current-carrying conductors.
(2) The conductors are 12 AWG copper.
(3) Not more than 20 current-carrying conductors are bundled, stacked, or supported on “bridle rings.”
A 60 percent adjustment factor shall be applied where the current-carrying conductors in these cables that are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing exceeds 20.
Click to expand...
The rule APPLIES to #12 [ item (2)]


I'll admit, the first line has me confused:
Adjustment factors shall not apply to Type AC cable or to Type MC cable without an overall outer jacket...

What does that mean?
The stripped portion in a panel?
 
Last edited:
Joe Villani said:
With 15 12/3 mc cables I am calculating at least 30 current carrying conductors so exception #5 (3) woulld not apply.
Click to expand...


How did you come up with 30 CCC's?
 
I would assume that these are three wire circuits with a neutral that is a CCC from a 208Y/120 volt system. That gives you 45 CCC's.
 
emahler said:
I would like to know how to get 3 circuit and a neutral from 12/3 MC.
Click to expand...


It's 2 circuits and a neutral. In a 208Y/120 volt system all three conductors would count as CCC's. So for 15-12/3 cables you would have 45 CCC's.
 
infinity said:
I would assume that these are three wire circuits with a neutral that is a CCC from a 208Y/120 volt system. That gives you 45 CCC's.
Click to expand...

i misread this as 3 circuits (minus the 'wire' part), but doesn't the type of load matter? linear vs. non-linear?
 
I'm assuming that there are 2 circuits with one neutral in each three wire cable. When fed form a 208Y/120 volt system all three conductors count as CCC's.
 
infinity said:
I'm assuming that there are 2 circuits with one neutral in each three wire cable. When fed form a 208Y/120 volt system all three conductors count as CCC's.
Click to expand...

trevor, i'm not doubting you, but do you know the article off hand? I was under the impression that the primary deciding factor was linear vs. non-linear.

I didn't know that 208V was different than 230V in considering whether is was a CCC or just carrying the unbalanced load.

But, looks like I learned something new.

Thanks
 
All the info can be found 310.15(B)(4) (a), (b) & (c).

If you use only two legs of a Wye system in a MWBC the neutral is always a current carrying conductor.

If you use all three legs of a Wye system in a MWBC the neutral is not a current carrying conductor unless the major portion of the load is non-linear.
 
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