# running NMSC through holes in joists question



## sparky1423 (Sep 18, 2010)

Technically, you can only run 3 sets of NM wire through a hole in a wood member because you end up having 3 current carrying conductors, and now you have to derate. If you actually took the time to derate, the ampaciities are usually fine. The inspectors do pay too much attention to this in residential dwellings because you are using a7/8 inch auger anyway. It's really had to fit more than 4 sets of NM. I have drilled larger holes and ran 5 to 6 pieces of NM cable at the service area and it always passed. I think it's a grey area in the code book with residential....hope this helps.


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## erics37 (May 7, 2009)

sparky1423 said:


> Technically, you can only run 3 sets of NM wire through a hole in a wood member because you end up having 3 current carrying conductors, and now you have to derate.


Not sure how your math works out there...

It would depend on what the particular circuits are wired to do. If they're 2-wire 120 volt circuits then you'd have a total of 6 current carrying conductors.


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## thegoldenboy (Aug 15, 2010)

Art. 310.15 (B)(2)(a) - 2008 (this article was changed minorly and renumbered in 2011)

*310.15 Ampacities for Conductors Rated 0–2000 Volts.
(A) General.
(1) Tables or Engineering Supervision.​*​​​​Ampacities for
conductors shall be permitted to be determined by tables as
provided in 310.15(B) or under engineering supervision, as
provided in 310.15(C).​
FPN No. 1: Ampacities provided by this section do not
take voltage drop into consideration. See 210.19(A), FPN
No. 4, for branch circuits and 215.2(A), FPN No. 2, for
feeders.
FPN No. 2: For the allowable ampacities of Type MTW
wire, see Table 13.5.1 in NFPA 79-2007,​​​​_Electrical Standard
for Industrial Machinery_.​
*(2) Selection of Ampacity.​*​​​​Where more than one calculated
or tabulated ampacity could apply for a given circuit
length, the lowest value shall be used.​
_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.​_FPN: See 110.14(C) for conductor temperature limitations
due to termination provisions.​*(B) Tables.​*​​​​Ampacities for conductors rated 0 to 2000​
volts shall be as specified in the Al
310.16 through Table 310.19, and Ampacity Table 310.20
and Table 310.21 as modified by (B)(1) through (B)(6).​FPN: Table 310.16 through Table 310.19 are application
tables for use in determining conductor sizes on loads calculated
in accordance with Article 220. Allowable ampacities
result from consideration of one or more of the following:
(1) Temperature compatibility with connected equipment,
especially the connection points.
(2) Coordination with circuit and system overcurrent protection.
(3) Compliance with the requirements of product listings
or certifications. See 110.3(B).
(4) Preservation of the safety benefits of established industry
practices and standardized procedures.​*(1) General.​*​​​​For explanation of type letters used in tables
and for recognized sizes of conductors for the various conductor
insulations, see Table 310.13(A) and Table
310.13(B). For installation requirements, see 310.1 through
310.10 and the various articles of this _Code_. For flexible
cords, see Table 400.4, Table 400.5(A), and Table 400.5(B).​
*(2) Adjustment Factors.​*(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.
lowable Ampacity Table
FPN No. 2: See 366.23(A) for adjustment factors for conductors
in sheet metal auxiliary gutters and 376.22(B) for
adjustment factors for conductors in metal wireways.​_Exception No. 1: Where conductors of different systems, as
provided in 300.3, are installed in a common raceway or
cable, the derating factors shown in Table 310.15(B)(2)(a)
shall apply only to the number of power and lighting conductors
(Articles 210, 215, 220, and 230).
Exception No. 2: For conductors installed in cable trays,
the provisions of 392.11 shall apply.
Exception No. 3: Derating factors shall not apply to conductors
in nipples having a length not exceeding 600 mm (24 in.).
Exception No. 4: Derating factors shall not apply to underground
conductors entering or leaving an outdoor
trench if those conductors have physical protection in the
form of rigid metal conduit, intermediate metal conduit, or
rigid nonmetallic conduit having a length not exceeding
3.05 m (10 ft) and if the number of conductors does not
exceed four.
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.​_(b)​​​​_More Than One Conduit, Tube, or Raceway. _Spacing
between conduits, tubing, or raceways shall be maintained.
(c) _Conduits Exposed to Sunlight on Rooftops. _Where
conductors or cables are installed in conduits exposed to
direct sunlight on or above rooftops, the adjustments shown
in Table 310.15(B)(2)(c) shall be added to the outdoor temperature
to determine the applicable ambient temperature
for application of the correction factors in Table 310.16 and
Table 310.18.​
FPN: One source for the average ambient temperatures in​various locations is the ASHRAE Handbook — _Fundamentals_.
FPN to Table 310.15(B)(2)(c): The temperature adders in
Table 310.15(B)(2)(c) are based on the results of averaging the​ambient temperatures.

You'll have to look the table up yourself.


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## rlc3854 (Dec 30, 2007)

sparky1423 said:


> Technically, you can only run 3 sets of NM
> 
> 
> 
> ...


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## thegoldenboy (Aug 15, 2010)

rlc3854 said:


> sparky1423 said:
> 
> 
> > Technically, you can only run 3 sets of NM
> ...


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