MC Cabe through metal studs.

[bhwolf@sbcglobal.net]

Ok, here is my question. t's sort of a two part-er. We have 2 (2) 3/4 flex and (1) 12/4 MC running through the same factory punched 1 1/2" X 3" hole in metal studs. Here's the question:

A. Is there any violationin running multiple (2 or more) fmc or MC cables through a factory metal stud hole.?

B. Can those cable's / flexs be tie wired together or do they have to be tied individually? (i.e. 3 separate tie wires for 3 separate cables/flexs) ?

The 3/4" flexs will each have (2) 208v circuits - 4 CCC x2 and the 12/4 is 3 CCC for a total of 11 CCC and the flex, if i understand the wording of the code is not a CBALE, therefor the "3 or more" CCC does not apply.

Any help would be appreciated, hopefully my question/s made sense. Thanks guys!!

btw.....29yrs old, SoCal, electrician for 9 yrs, and my dog's name is Cuda.

 

[Jim W in Tampa]

Your fine with it. Welcome to the forum.

 

[bhwolf@sbcglobal.net]

Jim, thanks for getting back to me, I really appreciate it. If you don't mind, could you please explain to me why it's ok? I took a bit of heat for it today, and I had no other argument for my case than "It doesn't say you cant......"

Again, thanks for the response, I appreciate you taking your time to help me out!!

 

[Pierre C Belarge]

Jim, thanks for getting back to me, I really appreciate it. If you don't mind, could you please explain to me why it's ok? I took a bit of heat for it today, and I had no other argument for my case than "It doesn't say you cant......"

Again, thanks for the response, I appreciate you taking your time to help me out!!

The NEC is a "permissive" document. Generally speaking, this means if there is no requirement for one to make an installation in a certain way, then one does not have to.
That is why you cannot find what you are looking for in the NEC, as there is no restriction to the number of cables in a boring or punch hole through framing.
What you do have to be aware of is 300.17. This helps give guidance when installing conductors and or cabling. Notice my use of terms..."GUIDANCE".
One wants to be careful when pulling cables through bored/punched holes, not to damage the cables.
When installing cable(s) through bored or punched holes of framing, securing in not required if the framing members are less than 24 inches apart from one another.

 

[George Stolz]

I disagree with the above.

First, I agree that a stud bay is not a raceway. A hole in a stud is not a raceway. That's the first principle.

However, once this principle is acknowledged, you've got one more issue:

310.15(B)(2)(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

310.15(B)(2)(c) More Than One Conduit, Tube, or Raceway. Spacing between conduits, tubing, or raceways shall be maintained.

So, if you take derating into consideration, your cables/raceways should be separated before the 24" mark, technically. At least, they should be separated by divvying them into secured bundles of 9 CCC's or less to avoid derating issues. This is usually easily accomplished in a commercial setting by installing a spanner bracket in the stud bay, and one-holing the cables to the spanner.

In a wood-framed environment, a couple 2x4's spanning the stud bay and stapled (as you would think of over a panel) one way, or stealing a bracket out of a bracket 3/0 round box and securing the cables to that would meet the requirement.

It's not the hole in the stud, as that's only paper-thin - it's the cables/raceways having consistent proximity that is the problem.

 

[augie47]

I bet that is looked at a number of different ways. 310.15(b)(2)(b) in the '08 Code states "spacing shall be maintained" but provides no specifics.
On the other hand it appears that 310.15(b)(a) exception #5 allows for up to 20 CCC with 12/2/or 12/3 MC bundled.
I would say one would encounter different calls from local AHJ with most accepting the install described by the OP especially if some effort was made to keep the raceways from being bundled full length.

 

[George Stolz]

The catch is, his exception wouldn't do him any good, throwing flex into the mix, would it?

 

[augie47]

I agree, but I would imagine that might influence ones perception of "spacing". If the Code allows 20 CCC with MC, I would have to admit I'd be hard pressed to get upset over the MC /flex combination when some spacing was provided in light of (b) simply stating "spacing shall be maintained".
To me, it certainly leaves the door open to some "interpretation"

 

[Pierre C Belarge]

There is no specific measurement for maintaining spacing of the cables when installing them. If one is to bundle them by means such as tie-wire or wraps, then I believe it is not difficult to determine that the cables are bundled.

As I have seen many thousands of times, when installing cables through framing, whether bored holes or metal framing, it is not generally considered bundling.
Therefore, as long as the cables can be installed without incurring damage, the only issue would be whether there is damage.
[of course there is also the issue of space from the front of the framing member-300.4(A)(1)]

 

[Flex]

Dont you have to derate if the hole in the 2x4 wood stud is fire caulked?