Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to codefaqs@gmail.com. Answers are based on the 2014 NEC.


Communications cable and 300.4(E)


In exposed or concealed locations under metal-corrugated sheet (screws running down through the roof) roof decking, Section 300.4(E) requires all cables, raceways or boxes to be installed so they are at least 1½ inches below the lowest surface of the roof decking to the top of the cable, raceway or box. An engineer and owner have directed us to install communications circuits in the webs above the steel truss, which violates 300.4(E). The engineer claims that this requirement does not apply to this installation, but he did not provide a Code section, and we do not want to violate the NEC. Is the engineer correct?


Yes, in this case, Section 300.4(E) does not apply. The answer begins in Section 90.3, which explains the arrangement of the NEC. Chapter 8 covers communications systems and is not subject to the requirements of chapters 1 through 7, except where the requirements are specifically referenced in a Chapter 8 article. Article 800 addresses communications circuits. Section 800.3, Other Articles, contains references in chapters 1 through 7 that will apply to the installation of communications circuits, and it does not reference 300.4(E).


It should be noted that there are other references throughout Article 800. For example, Section 800.24 for mechanical execution of work references 300.4(D) and 300.11. The intent of 300.4(E) is to prevent damage to raceways, cable, cable assemblies, boxes, etc., that contain energized conductors. While the engineer is correct that 300.4(E) does not apply here, it would be prudent to observe the spacing requirements of 1½ inches to prevent damage to the communication circuits.


Documenting torque values


According to the contract we signed on a new installation, we must provide the owner with documentation of termination of all conductors to the proper torque. Is it an NEC requirement to document torque values? We asked how they want it documented but did not receive a response. Is there a standard format?


The NEC requires terminations to be installed in accordance with equipment listing, labeling and instructions, as per Section 110.3(B). This means that all terminations marked with torque values or where instructions provide the torque values must be properly torqued. The NEC does not require documentation of torque values. See the informational note in 110.14.


I suggest you document the types of calibrated torque wrenches, ratchets and screwdrivers as needed, then build documents to list all terminations and torque values. Where devices or terminations are marked with a torque value or it is provided in the instructions, use that value. Where no torque value is provided, use NEC Annex I, Recommended Tightening Torque Tables from UL standard 486A-B. The 2017 NEC will clarify this requirement with a new Section 110.14(D), requiring a calibrated torque tool to be used to achieve the desired value.


Aluminum terminations


An increasing number of installations I am involved with use aluminum feeders for economical reasons. We were instructed on some jobs to use a compound for aluminum on all terminations, yet when working for another contractor, I have been instructed to not use a compound. This gets confusing in the field. Does the NEC require the application of a compound on aluminum terminations?


First and foremost, in Section 110.3(B), the NEC requires all installations of listed or labeled equipment to be installed and used in accordance with any instructions included in the listing or labeling. Therefore, aluminum conductors and associated lugs and terminations must be installed in accordance with all manufacturers’ instructions. When in doubt, contact the manufacturer.


Section 110.14 addresses electrical connections and requires devices, such as pressure terminal or pressure splicing connectors and soldering lugs, to be identified for the conductor material and be properly installed and used. This is to address issues that can occur between dissimilar metals. It is typical to see lugs dual-rated for both aluminum and copper conductor terminations as “Al/Cu.” 


This section also specifically prohibits conductors of dissimilar metals from being intermixed in a terminal or splicing connector where physical contact occurs between dissimilar conductors, such as copper and aluminum, unless the device is identified for the purpose and conditions of use. Again, this is where dual-rated terminations play a significant role.


This section requires any used compounds to be suitable for the use and to not adversely affect the conductors, installation or equipment, but it does not mandate the use of compounds. Where compression-type connectors are used for aluminum, they typically have the joint compound (oxide inhibitor) preinstalled. Where needed to retard oxidation, a conductor/connector-interface joint compound is used for aluminum, copper-clad aluminum and copper conductors.


In this case, the answer is in a National Electrical Contractors Association (NECA) standard that is jointly developed with the Aluminum Association. NECA/AA 104 2012, Recommended Practice for Installing Aluminum Building Wire and Cable, recommends a listed joint compound to be applied to the bare conductor after it has been wire brushed. The joint compound provides a coating that remains on the conductors’ surface, preventing moisture and other contaminants from contacting the connection area.


Emergency lighting requirement


During a recent commercial renovation project, we encountered several interesting issues with emergency lighting. The building is supplied by a 15-kilovolt service and steps down to 480/277-volt with a single large switchboard supplying power throughout the structure. A standby generator supplies power for the emergency system. We scheduled a complete shutdown on a weekend to get into the switchboard. It is a good thing we had multiple battery-supplied portable lighting units on-site, because no emergency lighting existed in the electrical equipment room. This is obviously poor design. But is there an NEC requirement for emergency lighting in electrical equipment rooms? If not, there should be. We also had an issue with the electrical inspection of emergency lighting. The inspector stated that the NEC required two branch circuits so that, if one failed, the other would provide some level of light. We could not find such a requirement. Can you help?


The answer to both of your questions is in Section 700.16, which contains requirements for emergency illumination. It must be noted that the NEC contains minimum installation requirements but does not typically mandate where emergency lighting is required. See Informational Note 3 in Section 700.1, which informs the Code user that NFPA 101 2012, Life Safety Code, provides specific requirements for locations where emergency lighting is considered essential to life. In the 2014 NEC revision cycle, Section 700.16 was changed to include a requirement for illumination in the area of the disconnecting means required by 225.31 and 230.70, as applicable, where the disconnecting means are installed indoors and an emergency system exists. This is essential for maintenance personnel in the event of the loss of normal power.


There is no NEC requirement for two emergency circuits to supply lighting to any area. However, Section 700.16 requires emergency lighting systems to be designed and installed so that the failure of any individual lighting element, such as the burning out of a lamp, cannot leave in total darkness any space that requires emergency illumination. The focus of this rule is any “individual lighting element” cannot leave any space in total darkness. The example “individual lighting element” given is “such as the burning out of a lamp” but would include a ballast, battery, etc. Where that is possible, more than one luminaire in the area must be positioned so that the loss of one luminaire will not leave a space in total darkness.


AWG and TW wire?


For years, I have wondered why the wire gauge sizes we use are essentially backward. Why is a No. 10 AWG larger than a No. 12 AWG? It seems that we have it backward, and there must be a reason. Why do we still have ampacities for TW wire in the NEC? I have not seen TW since my apprenticeship, and that was a long time ago.


The American Wire Gauge system (AWG) was developed by J.R. Brown and Sharpe around 1857 to standardize wire sizes in North America. Prior to the AWG system, each manufacturer had its own method and numeric values for conductor sizes. There is a valid reason why this system places a smaller value on a larger conductor. The numeric values are based on the number of sizing dies the wire needs to be drawn through to reach the correct diameter. For example, there would be 10 sizing dies to make a No. 10 AWG, and there would be an additional two sizing dies need to reduce the diameter and make a No. 12 AWG.


While TW wire is not commonly seen in construction, it is still manufactured and used for many purposes, including internal appliance wiring. It is also used for grounding and bonding in some applications, thereby requiring the NEC to address TW conductor ampacity.