Thread: Romex protection - New construction

Guy who is building a garage asked me these two questions. If he builds it with metal studs and sheaths the exterior but no sheetrock on the interior - can he just tie the romex to the interior part of the metal studs? If he builds it with wood studs and drills holes for the romex - sheaths the exterior but leaves the interior uncovered is that OK? I say both are incorrect becasue of NEC 334.15 - exposed work. Am I correct or am I misinterpreting the code or is another part more applicable?

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Originally Posted by Bob Spermo

Guy who is building a garage asked me these two questions. If he builds it with metal studs and sheaths the exterior but no sheetrock on the interior - can he just tie the romex to the interior part of the metal studs?

No, he needs to run it through the pre-punched holes in the metal studs, or punch holes as needed, and use the proper plastic bushings too.

He also needs to make sure that the nearest edge of the NM cable in its strapped in place position is more than 1-1/4" back from the face of the studs.

If he builds it with wood studs and drills holes for the romex - sheaths the exterior but leaves the interior uncovered is that OK?

Yes, if the nearest edge of the NM cable in its strapped in place position is more than 1-1/4" back from the face of the studs.

I say both are incorrect becasue of NEC 334.15 - exposed work. Am I correct or am I misinterpreting the code or is another part more applicable?

Correct, you are incorrect and you are misinterpreting it.

Here is the definition of "exposed" work:
- Exposed (as applied to wiring methods). On or attached to the surface or behind panels designed to allow access.

Start here:
- 334.17 Through or Parallel to Framing Members.
- - Types NM, NMC, or NMS cable shall be protected in accordance with 300.4 where installed through or parallel to framing members. Grommets used as required in 300.4(B)(1) shall remain in place and be listed for the purpose of cable protection.

Then go to 300.4(A)(1)&(2) and (B)(1)&(2): (bold and underlining are mine)
- 300.4 Protection Against Physical Damage.
- - Where subject to physical damage, conductors shall be protected.
- - (A) Cables and Raceways Through Wood Members.
- - - (1) Bored Holes. In both exposed and concealed locations, where a cable- or raceway-type wiring method is installed through bored holes in joists, rafters, or wood members, holes shall be bored so that the edge of the hole is not less than 32 mm (1¼ in.) from the nearest edge of the wood member. Where this distance cannot be maintained, the cable or raceway shall be protected from penetration by screws or nails by a steel plate(s) or bushing(s), at least 1.6 mm ( in.) thick, and of appropriate length and width installed to cover the area of the wiring.
- - - - Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
- - - - Exception No. 2: A listed and marked steel plate less than 1.6 mm ( in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.
- - - (2) Notches in Wood. Where there is no objection because of weakening the building structure, in both exposed and concealed locations, cables or raceways shall be permitted to be laid in notches in wood studs, joists, rafters, or other wood members where the cable or raceway at those points is protected against nails or screws by a steel plate at least 1.6 mm ( in.) thick, and of appropriate length and width, installed to cover the area of the wiring. The steel plate shall be installed before the building finish is applied.
- - - - Exception No. 1: Steel plates shall not be required to protect rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing.
- - - - Exception No. 2: A listed and marked steel plate less than 1.6 mm ( in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.
- - (B) Nonmetallic-Sheathed Cables and Electrical Nonmetallic Tubing Through Metal Framing Members.
- - - (1) Nonmetallic-Sheathed Cable. In both exposed and concealed locations where nonmetallic-sheathed cables pass through either factory- or field-punched, cut, or drilled slots or holes in metal members, the cable shall be protected by listed bushings or listed grommets covering all metal edges that are securely fastened in the opening prior to installation of the cable.
- - - (2) Nonmetallic-Sheathed Cable and Electrical Nonmetallic Tubing. Where nails or screws are likely to penetrate nonmetallic-sheathed cable or electrical nonmetallic tubing, a steel sleeve, steel plate, or steel clip not less than 1.6 mm ( in.) in thickness shall be used to protect the cable or tubing.
- - - - Exception: A listed and marked steel plate less than 1.6 mm ( in.) thick that provides equal or better protection against nail or screw penetration shall be permitted.

Jerry,

I guess my problem is the definition of "physical damage". If the wires run through wood studs and are not protected by sheetrock isn't physical damage to the wire possible?

Originally Posted by Bob Spermo

I guess my problem is the definition of "physical damage". If the wires run through wood studs and are not protected by sheetrock isn't physical damage to the wire possible?

Bob,

No question that it "is" possible.

However, you were asking about the code and how it addresses the issue, not how I would do it. Remember, codes are only "minimum" standards and requirements, not good, better or best practices.

If *I* were to do that, first and foremost, I would install drywall inside when done and that would take care of that issue; second, if for some reason I did not install drywall, then I would run the wiring in Sch 40 PVC, however ... keep in mind that even Sch 40 PVC *is not rated for* "protection from physical damage", you would need Sch 80 for that purpose if going with PVC.

In your mind, then, would running that in Sch 80 PVC be "overkill"?

If "protection from physical damage" is your concern, that would be the way to do it - Sch 80 PVC or some metallic conduit.

Originally Posted by ben jacks

Hi Bob, Another alternate, if yet to be mentioned, if running in metal or wood studs and leaving exposed, would be using MC for wiring protection. [330.10(A)(4)]

Ben,

Except that Bob's concern is "physical damage" and MC is not rated as protection from "physical damage" - it too needs to be protected from physical damage, just like NM cable needs to be protected from physical damage.

- 330.12 Uses Not Permitted.
- - Type MC cable shall not be used under either of the following conditions:
- - - (1) Where subject to physical damage
- - - (2) Where exposed to any of the destructive corrosive conditions in (a) or (b), unless the metallic sheath or armor is resistant to the conditions or is protected by material resistant to the conditions:
- - - - a. Direct buried in the earth or embedded in concrete unless identified for direct burial
- - - - b. Exposed to cinder fills, strong chlorides, caustic alkalis, or vapors of chlorine or of hydrochloric acids

When Bob applies the "potential for physical damage" to the wiring run through the framing members, his potential for such physical damage will apply to all wiring methods which are not rated for providing protection from physical damage.

Basically, that leaves the following wiring methods for use - as identified in 300.5(D)(4) as being suitable for use as protection from physical damage:
- (4) Enclosure or Raceway Damage. Where the enclosure or raceway is subject to physical damage, the conductors shall be installed in rigid metal conduit, intermediate metal conduit, Schedule 80 PVC conduit, or equivalent.

(whatever "or equivalent" is)

Being as I doubt that guy is going to be able to run rigid or intermediate metal conduit, that leaves Sch 80 PVC conduit as the remaining choice.