MC Cable

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henbra

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A three story residential apartment building with 80 units and underfloor garage is proposed to be wired with MC cable. The Electrical room and meters are in the garage level.The MC cable will go from the garage enclosed in a sheetrock chase up against the underside of the garage ceiling and up via shaft.
1. Do I have to derate the ampacity of the MC cable since the 80 MC cables(100 A) will be stacked or bundled without spacing in the shaft. 2. Is there a Code section that explains that issue.
 
Re: MC Cable

Didn't you ask the same question about SER cable?

You will have the same issues with MC cable that you do with SER.

The answer is yes to both questions, however, the NEC does not really "explain" anything, it simply states a rule that must be followed.
 
Re: MC Cable

Have you considered adding additional electrical rooms?

Running 80 feeders into one electrical room sounds like an awfully poor design.
 
Re: MC Cable

310.16
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.
Spacing is not defined in this section. But IMO if you spaced these apart so that the heat could disapate then you would be OK. What is that space, I have no idea. As others have said there are a lot ways to do this other than rope. Have you even given any thought to voltage drop for these feeders?
 
Re: MC Cable

Please let me know your opinion about 392.11 if the cables are installed in cable tray, in a sigle layer with no less than one cable diameter. The derating is limited to the conductors in the cable and not to the conductors in the cable tray. Since I have only 3 conductors per cable no derating is necessary.
 
Re: MC Cable

Originally posted by henbra:
Since I have only 3 conductors per cable no derating is necessary.
Click to expand...
Could you clarify what you mean here? For the purposes of derating, you will only consider 3 conductors (2 live and 1 grounded) as current carrying, but you still need the fourth conductor for grounding.

You are correct in that you only have 3 current carrying conductors so derating is not necessary of the cable itself.

[ March 03, 2005, 06:25 PM: Message edited by: peter d ]
 
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