MC cable bundleing

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AKsparky1

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I would like to know where in the NEC is the language that says there is no bundleing requirement like that with NM-B. I understand that the metal clad sheath prevents extra heating in the conductors but does this mean I can run as many MC cables as I want to through bored holes and parralel to frameing members?
 
Derating does apply to MC cables but the NEC provides some relief from the usually more than 3 CCC derating rules. If you take note this only applies to #12 AWG conductors.

310.15(B)(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 in-
stalled without maintaining spacing, are stacked, or are
supported on?bridle rings.?
(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...
 
AKsparky1 said:
I would like to know where in the NEC is the language that says there is no bundleing requirement like that with NM-B. I understand that the metal clad sheath prevents extra heating in the conductors but does this mean I can run as many MC cables as I want to through bored holes and parralel to frameing members?
Click to expand...

Your expectation does not bear out the rules/laws of physics. Metal clad would be a better heat conductor than a nonmetallic material, however when your trap the heat by bundling the overall heat dissipation would only be different on the outer surface of the bundle and your heat-up/cool-down time constant would change, but the temperatures and the equilibrium point would only change slightly, not sufficiently different enough to establish different bundling rules.
 
And let's not forget about 310.60 (B) (1)

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

That would mean one can have unlimited number of MC cables for up to 10 ft circuits are over 100 ft. Which is usually occurs.
 
darekelec said:
And let's not forget about 310.60 (B) (1)

Exception: Where two different ampacities apply to adjacent portions of a circuit, the higher ampacity shall be permitted to be used beyond the point of transition, a distance equal to 3.0 m (10 ft) or 10 percent of the circuit length figured at the higher ampacity, whichever is less.

That would mean one can have unlimited number of MC cables for up to 10 ft circuits are over 100 ft. Which is usually occurs.
Click to expand...

You're correct that one is often overlooked. I think that you meant 310.15(A)(2)Ex. 310.60 is for Conductors Rated 2001 to 35,000 Volts. ;)
 
infinity said:
Derating does apply to MC cables but the NEC provides some relief from the usually more than 3 CCC derating rules. If you take note this only applies to #12 AWG conductors.
Click to expand...

310.15(B)(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.
Click to expand...

What is meant by 315.15(B)(4)(a)? How can MC not have an outer jacket? The MC=metal clad is the jacket.:?
 
Volta said:
An overall outer jacket. Like a non-metallic sheath over the metallic sheath, say for wet locations.
Click to expand...

That's correct, they mean cable like direct burial MC, sometimes called parking deck cable.
 
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