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Is it code-compliant to install Type NM cable exposed in an attached residential garage? How about a detached garage?

Posted By Charles Palmieri, Saturday, September 01, 2012
Updated: Monday, February 04, 2013

Question

Is it code-compliant to install Type NM cable exposed in an attached residential garage? How about a detached garage? What about a detached residential building such as a storage shed? BG

Answer

Thank you for the inquiry. For clarity, I will frame my response. First, I will substitute the term residential with the term dwelling which is defined in NEC Article 100. Second, I will consider the attached garages or detached garages and storage sheds to be directly associated with one- and two-family dwellings. Third, all structures considered will be of Types III, IV, and V construction. For this discussion, I will focus my response to the language of the 2011 National Electrical Code and before I begin, I will state my understanding of your question. You wish to know if nonmetallic-sheathed cable is permitted to be installed as an exposed wiring method in an attached or detached garage or in a detached building such as storage shed. Whenever there is a need to determine the permitted uses of any wiring method, I begin by reviewing the XXX.10 Uses Permitted section for that specific wiring method. I will start by reviewing 334.10 which generally states that nonmetallic-sheathed cable is permitted to be used in accordance with its following five (5) listed items. For this discussion we will only consider the language in list items (1) and (3).

The language of 334.10(1) permits the use of nonmetallic-sheathed cable in one- and two-family dwellings including their attached or detached garages and their storage buildings. This section was revised for the 2011 edition of the NEC by inserting the words "and their attached or detached garages, and their storage buildings” after the word "dwellings.” The new language was added to make it clear that the use of nonmetallic-sheathed cable as an exposed wiring method in one- and two-family dwellings, including their attached and detached garages and storage sheds, is permitted. To further support this conclusion, I look at the previous editions’ language in 334.10(1) which stated that nonmetallic-sheathed cable was permitted in one- and two-family dwellings. This language did not prohibit exposed cable installations in a dwelling or its attached garages, but it was silent in regard to installations in detached garages or other detached structures associated with a dwelling.

Under previous editions of the Code, installations in detached structures associated with dwellings were guided by the language of 334.10(3). That section addresses installations of nonmetallic-sheathed cable in other structures which are not dwellings and the language gives us two basic requirements. (1) It restricts the use of the cable to those structures that conform to Types III, IV, and V construction and (2) it requires that the cable be concealed within walls, floors, and ceilings that provide a thermal barrier of material that has at least a 15-minute finish rating.

Keeping all this in mind and upon review of sections of 334.10(3) and the revised language of 334.10(1), it is clear that nonmetallic-sheathed cable is permitted to be installed exposed in one- and two-family dwellings, their attached and detached garages, and their storage buildings. It is additionally important to note that regardless of the building’s condition of occupancy where the cable is installed exposed, it must comply with the provisions of 334.15; and if it is determined that the installation is subject to physical damage, then guarding in accordance with 334.15(B) must be considered.

Additional sections of the Code relevant to the installation and routing of the cable will provide guidance for a compliant installation (see 300.4, for example). It is also helpful to note that structures are grouped into five general types. These types are summarized in the Informative Annex E titled, "Types of Construction,” which may be found on page 814 of the 2011 NEC (soft cover). I hope this information is helpful.

Charles Palmieri
IAEI Principal Member, CMP-7

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Tags:  Focus on the Code  September-October 2012 

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We have some radio equipment that uses a screw-type fastener to bond or attach the grounding conductor to the antenna assembly. Can this screw be any ordinary screw, or does it need to be a “listed” s

Posted By Tom Moore, Saturday, September 01, 2012
Updated: Monday, February 04, 2013

Question

We have some radio equipment that uses a screw-type fastener to bond or attach the grounding conductor to the antenna assembly. Can this screw be any ordinary screw, or does it need to be a "listed” screw meeting the requirements of 250.70 or, perhaps, 250.8? Does the screw need to be "green” in finish? Do the grounding and bonding rules in Article 250 apply to radio and television equipment? Or is Article 810 the only applicable rules that would apply? DB

Answer

Thank you for your correspondence. The question presented is frequently discussed by many with diverse results. Radio equipment as referenced in the question falls under the scope of Article 810 of the NEC.

We first need to point out that the term grounding conductor as referenced in the question and used in previous editions of the NEC has been revised to three more appropriate terms: grounding electrode conductor, bonding jumper, or bonding conductor. CMP-16 accepted these revisions throughout Article 770 and all Chapter 8 articles to provide consistency and correlation with defined grounding and bonding terms in Article 100, and to avoid the use of an undefined term in the communications articles.

Let’s begin with the first part of your question. Section 250.70 does apply for the connection to grounding electrodes as referenced in 810.21(K). If I understand the question correctly, we are referring to the grounding electrode conductor or bonding conductor termination to the equipment. Section 810.21 is silent as to the requirements for connection of the grounding electrode or bonding conductor to the equipment; therefore, the listing requirements of the radio equipment need to be followed.

As for the screw terminal, Chapter 8 has no requirements that would require the screw to be identified by a green color.

In the third part of the question dealing with the application of grounding and bonding rules of Article 250, we need to review the code arrangement in 90.3. The second paragraph of 90.3 points out that Chapter 8 is basically a stand-alone chapter, and that Chapters 1 through 7 only apply where specifically referenced in Chapter 8. One example is the reference to 250.70 in 800.21(K) and discussed above.

Tom Moore
IAEI Representative, Chairman-CMP-16

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Tags:  Focus on the Code  September-October 2012 

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