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 2017 NEC.


Parallel equipment 
grounding conductors


Our designers are considering an installation of nonmetallic cable tray with MC cables for a parallel feeder, which brought up some questions. Where equipment grounding conductors (EGCs) are installed for parallel feeders, the NEC seems to contradict itself repeatedly. It is permissible to install electrical metallic tubing (EMT) and use it as an EGC without a conductor-type EGC installed. However, where we install a conductor-type EGC in a parallel feeder installed in EMT, it must be a full-size conductor EGC based on the feeder overcurrent protection. Why? Now I see we can run MC cable in parallel with undersized EGC conductors in nonmetallic cable tray if a single, full-size EGC is run separately in the same tray. How does that comply with 300.3(B)?


The sizing requirements for EGCs installed in parallel feeders have long been debated and will continue to be for many NEC cycles. Section 250.118(4) recognizes EMT as a permitted EGC. Note that this permission does not limit the size of the upstream overcurrent protective device (OCPD). Why, then, would the NEC require conductor-type EGCs to be full size if one chooses to install them? I have been asked this question many times. I have also asked this question many times and never received a technical answer to substantiate the requirement. 


I agree with you. If EMT (note that both IMC and RMC are also recognized in 250.118 as an EGC) is used for parallel feeders, smaller EGCs supplementing the raceway should be permitted. It is imperative to note that, since EMT is permitted to act as an EGC alone, the conductor type EGCs would be supplemental only. When we add conductor-type EGCs to a parallel installations of metal raceways that are permitted to act alone as an EGC, we begin to question the raceway EGC. If that is the basis for full-size conductor type EGCs, we need to revisit 250.118.


As you point out, a revision in Section 250.122(F)(2) now permits parallel MC cables (with undersized EGCs) in a nonmetallic cable tray with a single and separate full-size conductor type EGC installed. I agree that this permissive requirement is in direct conflict with 300.3(B), which requires all circuit conductors—including grounded conductors, EGCs or bonding conductors—where installed to be in the same cable assembly. Where we install a full-size EGC outside of metal jacketed cable assemblies, the separate EGC is effectively shielded from the circuit conductors inside. There is no doubt that using cable assemblies, such as MC cable for parallel feeders, is extremely popular. The manufacturers of these cables stock multiple configurations, including those with larger EGCs, that are intended for parallel arrangements. This allows the installer to purchase a cable assembly with a full size EGC.


Minor damage?


Section 300.4 contains a requirement to protect conductors, raceways and cables from physical damage. The informational note confuses me because it basically permits physical damage. Am I reading it wrong?


The note in Section 300.4 does not contain a requirement. Section 90.5(C) explains that notes in the NEC are explanatory only and are not an enforceable part of the Code. This note simply recognizes that minor damage to a raceway, cable armor or cable insulation does not necessarily violate the integrity of either the contained conductors or the conductors’ insulation.


For example, if an installation of electrical metallic tubing (EMT) has a small dent in the raceway that occurs during work in an electrical closet, should the electrical inspector fail the installation? Should the installer be required to remove and replace the EMT? No. In my opinion, this note is simply recognizing that common sense should prevail when something very minor occurs that does not impact “the integrity of either the contained conductors or the conductors’ insulation.”


Definitions not in Article 100?


It has been my understanding that, if the NEC defines a term that is used in more than one article, that definition has to be located in Article 100. Why are the definitions of raceways contained within the raceway articles and not in Article 100?


The NEC is written in a specific style to ensure consistency, clarity and usability. Technical committee members are required to develop new NEC requirements and revise existing text in compliance with the NEC Style Manual. This document outlines the NEC writing style and is available to the public to view or download online. All definitions must be listed in alphabetical order. A definition is not permitted to contain the defined term and cannot contain a requirement. Definitions that appear in two or more articles are required, in general, to be located in Article 100. If a definition is located in an individual article, it must be placed in the second section (e.g., Section 240.2). There is no requirement that would prevent a definition in the second section of an article from applying throughout the NEC.


The reference in your question is to the raceway articles in the NEC. Yes, the definitions are in the second section of the individual articles, and those raceways are also referenced in multiple other articles. In this case, it is logical to leave the definition in the individual article. There are many other defined terms within in the second section of an individual article that cannot be used elsewhere in the NEC. This issue is currently being addressed by a ­correlating-committee-appointed task group that will likely submit public inputs in the 2020 NEC revision cycle to provide additional clarity for users of the NEC.


DC disconnects, 60 volts


Why was the threshold changed from 50 to 60 volts (V) in the requirement for a disconnecting means for DC systems?


The 2017 NEC had multiple revisions related to the previous 50V threshold for DC systems. Section 480.7(A) was revised to require a disconnecting means for all ungrounded conductors from a stationary battery system with a voltage over 60V DC. The concern was that, in many cases, the electrical inspector required a disconnecting means for a nominal 48V DC battery system because the charging float voltage was more than 50V.


The NEC defines “voltage, nominal” and a new Informational Note No. 3 was added to explain that, in some cases, a battery source may be considered to be rated at nominal 48V DC but may have a charging float voltage up to 5V. This is why we moved up to 60V. Throughout the NEC, where the term “voltage” is used, it is the value of voltage at which the circuit operates. See Section 110.4.


Service-supplied 
equipment barriers


At a recent Code-change class, I learned the 2017 NEC now requires all service-supplied panelboards to have barriers to protect from inadvertent contact of the line side service conductors. I was very surprised to hear that switchboards also are included and require the same barriers. The last few projects we were on included service-supplied switchboards and there were no barriers. Is that a manufacturer’s responsibility?


Section 408.3(A)(2) requires barriers in all service-supplied panelboards, switchboards and switchgear to ensure that no uninsulated, ungrounded service busbar or service terminal is exposed to inadvertent contact by people or maintenance equipment while servicing load terminations.


While panelboards were added to this requirement in 2017, switchboards have been required to have these barriers where they are service-supplied for decades. The installer is responsible for the barriers to prevent inadvertent contact. When we purchase a switchboard, the manufacturer does not know if it will be service- or feeder-supplied. The switchboard manufacturer can provide the necessary barriers or a field-installed kit for the contractor to put in place. 


In my opinion, this revision is long overdue. Panelboard manufacturers are now supplying field-installed kits to provide protection from inadvertent contact with the line-side service. These field-installed kits may also be used in feeder-supplied equipment. Where a service- or feeder-supplied main overcurrent protective device is opened in a panelboard without barriers, there are exposed energized conductors and circuit parts on the line side. Where these barriers are installed, there are no exposed energized conductors or circuit parts and an electrically safe work condition (as required in NFPA 70E) can be established.


The NEC and underground mines


The company we work for does a fair amount of electrical installations in mines in our area. We recently received training on electrically safe work practices because NFPA 70E now applies to mining installations. However, we were told that the NEC requirements for temporary power do not apply. Why does NFPA 70E apply here but not the NEC?


The 2015 edition of NFPA 70E deleted Section 90.2(B)(2), which had previously exempted mining operations. This was due to an arc-flash-hazard alert issued by the Mine Safety and Health Administration that referred to the use of NFPA 70E as a best practice to protect workers from arc flash hazards. There was no change in the NEC; mines are still not covered in the Code as per Section 90.2(B)(2).