I am re-doing the wiring in my home and I have encountered a situation where I need to run 4 sets of 12-2 NM-B (Romex) wire from my attic down to the same fixture. Per 334.30, I am allowed to leave cable free-hanging where it runs through a finished wall per section 334.30 B-1 of the NEC:
334.30 Securing and Supporting. Nonmetallic-sheathed cable shall be supported and secured by staples, cable ties, straps, hangers, or
similar fittings designed and installed so as not to damage the cable,
at intervals not exceeding 1.4 m (4 1⁄2 ft) and within 300 mm (12 in.)
of every outlet box. junction box, cabinet, or fitting. Flat cables
shall not be stapled on edge. Sections of cable protected from
physical damage by raceway shall not be required to be secured within
the raceway.(A) Horizontal Runs Through Holes and Notches. In other than
vertical runs, cables installed in accordance with 300.4 shall be
considered to be supported and secured where such support does not
exceed 1.4-m (4 1⁄2-ft) intervals and the nonmetallic- sheathed
cable is securely fastened in place by an approved means within 300 mm
(12 in.) of each box, cabinet, conduit body, or other
nonmetallicsheathed cable termination.FPN: See 314.17(C) for support where nonmetallic boxes are used
(B) Unsupported Cables. Nonmetallic-sheathed cable shall be permitted to be unsupported where the cable:
(1) Is fished between access points through concealed spaces in finished buildings or structures and supporting is impracticable.
(2) Is not more than 1.4 m (4 1 ⁄2 ft) from the last point of cable support to the point of connection to a luminaire or other piece of electrical equipment and the cable and point of connection are within an accessible ceiling
However, this also leaves me with some concern about code compliance regarding "bundling" or "not maintaining proper spacing" of the multiple wires within the wall cavity without having to derate the ampacity of the cables. Therefore, I am looking for a code compliant way of running the wires without being required to derate the ampacity of the cables.
The (vague) definition of bundled from section 520.2 of the NEC and an article that speaks to "not maintaining" spacing for NM-type cabling.
520.2 Definitions.
Bundled. Cables or conductors that are tied, wrapped, taped, or otherwise periodically bound together.
…
334.80 Ampacity. The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15.
…
310.15 Ampacities for Conductors Rated 0–2000 Volts. …
(B) Tables
…
(3) 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)(3)(a). Each current-carrying conductor
of a paralleled set of conductors shall be counted as
a current-carrying conductor.
If absolutely necessary, I could cut a small (1-gang or 2-gang sized) hole on the wall near the ceiling to secure the wiring, but this would be non-ideal and I cannot seem to find any solutions that would prevent my bundling problem for running along the framing member in any event. I have considered options like this multiple cable staple, but it seems to only aid with article 300.4 d (keeping multiple wires 1.25" away from the edge of frame members), but makes no claims about aiding maintaining proper spacing between the wires for runs greater than 24" as I cannot find anywhere that "proper spacing" is defined for NM-type cabling.
Of course, maybe I am worrying about this derating for business for naught. I am running the four cables to power lighting and one switch that I am using requires a direct connection to neutral. That said, I would still like to know if there is an NEC-approved (year 2008 or newer) way to run the four wires without having to derate them.
Best Answer
The derating would only occur if there is a section 24 in. long or more, where the cables are "bundled" together (from my understanding).
If the cables are run through a joist cavity, they'll be "bundled" for 1 1/2" - 3" at the top plate, and 1 1/2" - 3" at the bottom of the wall. Each of which is far under the 24 in. limit. Where the cables dangle through the cavity, they are not wrapped, taped, or bound together. They are only "bundled" for a short distance while they enter/leave the cavity.