MC Cable Derating

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JFletcher said:
So you are agreeing with my initial assessment in the previous post?

There is nothing in the original post that mentions neutrals at all. Could be 208V 3ph equipment. ofc (of course), all three conductors would be current-carrying then, and they'd also all be CCC with 208V 1ph with neutral. At least that is the assumption we both made as 45% applies to 21-30 CCC. In lieu of other pertinent information, like 'super sparky ran 10/3 to 208V lighting or water heaters' (that don't use a third CCC, hence we can ignore it for calculations), don't we have to assume that all 3 conductors are current carrying? The circuits come from a 208Y/120V 3ph panel.



eta: dunno about poorly worded, but I find it a terrible question nonetheless. Is there ANY real world application where the question would be applicable?
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Agreed. Posting from memory. I must have missed the 120/208 panel statement initially.

Real world application? Wouldn't put it past someone somewhere to try it. ;)
 
luckylerado said:
Where is everyone getting 45%? Bundling MC is addressed in 310.15(B)(3)(a)(5) and requires a 60% adjustment for this scenario. What am I missing?
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Nothing. It is I (or we if I am permitted to speak for the others). You are correct. 60% adjustment. :ashamed1:
 
luckylerado said:
Where is everyone getting 45%? Bundling MC is addressed in 310.15(B)(3)(a)(5) and requires a 60% adjustment for this scenario. What am I missing?
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Because the way the notation for 60% is mentioned in the NEC, it makes ME think that 24 CCC, as the OP has, wouldn't fall under its notation to the exception, that 24CCC in tightly bundled MC would fall under 310.15(B)(2)(a).

If you had 400 MC cables with 1200 CCC bundled together, would it be 60%, or 35? Preposterous, yes, but no more so than the OP's test question.
 
JFletcher said:
Because the way the notation for 60% is mentioned in the NEC, it makes ME think that 24 CCC, as the OP has, wouldn't fall under its notation to the exception, that 24CCC in tightly bundled MC would fall under 310.15(B)(2)(a).

If you had 400 MC cables with 1200 CCC bundled together, would it be 60%, or 35? Preposterous, yes, but no more so than the OP's test question.
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Where is there room to interpret this as anything other than what it says? Is it written differently in 17? 400 MCs would be 60%

(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.
 
luckylerado said:
Where is there room to interpret this as anything other than what it says? Is it written differently in 17? 400 MCs would be 60%

(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.
Click to expand...

Because it is written under the exceptions. Because it is not its own subsection, I could argue it's not applicable, that the 45% or 35% rating applies. Devil's advocate?

eta: I'm still looking at the 2008 NEC.
 
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