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 [email protected]. Answers are based on the 2014 NEC.


Signage


There is a label on the service equipment in a midrise condominium we are working on that warns about opening the grounding electrode conductor if the generator is running. Our scope of work is to relocate two feeders to accommodate new retail stores on the ground floor, and we are not doing anything with the grounding electrode conductor. We will be shutting down the service for around 30 minutes at some point, and that will start the emergency generator. Is the label on the service equipment a Code requirement or something that an engineer mandated?


The label you mention is an NEC requirement. It is required to warn installer/maintainers that there is an alternate source of power that has a grounding electrode connection through the equipment that has the label applied. This labeling is safety-driven and warns of a potential shock hazard, which can occur, for example, where service equipment is being replaced.


If an alternate power source is available due to the presence of an emergency, legally required standby or optional system, it is likely that the alternate source will be energized during the service replacement. In most cases, these alternate sources (e.g., generators) are not separately derived due to a solid connection to the grounded conductor of the service-supplied system in a transfer switch. Through that grounded conductor connection, the alternate system is grounded through the service grounding electrode system. If the alternate system is energized and someone opens the grounding electrode conductor or bonding jumper connection to the grounding electrode, a shock hazard exists and is supplied by the alternate source. This labeling requirement exists for emergency systems in 700.7(B), legally required standby systems in 701.7(B) and for optional standby systems in 702.7(B). The NEC provides prescriptive text for the label as follows:


WARNING

SHOCK HAZARD EXISTS 
IF GROUNDING

ELECTRODE CONDUCTOR OR BONDING JUMPER

CONNECTION IN THIS 
EQUIPMENT IS REMOVED

WHILE ALTERNATE SOURCE(S) 
IS ENERGIZED.


Manufactured buildings


We just finished working on six apartment units that came to the site premanufactured and prewired. Outside of supplying the units with feeders and making splices and wiring hot water heaters, they were completely finished. We treated them as a standard home, but the NEC contains provisions for manufactured buildings such as these. What rules in the NEC apply?


Article 545, Manufactured Buildings, would not apply to a manufactured home as seen in the definition in Section 545.2. The term “manufactured building” does not include manufactured homes, mobile homes, park trailers or recreational vehicles. Article 550 provides requirements for mobile homes, manufactured homes and mobile home parks. As your question points out, a manufactured home is essentially complete when it arrives on-site. Article 550’s requirements must be observed during the off-site electrical installation in the manufactured home.


Article 550 contains specific requirements that an electrical contractor must comply with, including, but not limited to, service and feeder requirements. 


Ambient temperatures


As an electrical contractor and part-time JATC instructor, I am frequently asked about ambient temperature ranges in the NEC. How does one know what the ambient temperature is in a given space? Without the ability to identify the right temperature value, how does one apply the ampacity tables? I see those ranges as subjective and a source of dispute, especially when a lower temperature will offer a higher ampacity allowance. I see the informational note in the rooftop sunlight section referring to the ASHRAE Handbook as optional and only intended for the “rooftop rule,” which we will see substantially reduced in 2017. Can you help? Another issue that is always asked is what “maintaining spacing” means.


Ambient temperature is essentially the temperature of the area surrounding a conductor or other piece of electrical equipment. In a controlled environment, the ambient temperature is the room temperature. These temperatures vary based on location.


For example, if electrical equipment and conductors are installed in a conditioned space that never gets above 75°F, the ambient temperature is the same. Where electrical equipment and conductors are installed in mechanical or attic spaces, the temperature will be significantly higher. Data is available for such spaces through an internet search, and an informational note mentions other resources, such as the ASHRAE document (outdoor temperatures).


The NEC cannot begin to identify all possible ambient temperature values. Second-level subdivision 310.15(B)(3) provides requirements for ­ampacity-adjustment factors. In 310.15(B)(3)(a), this requirement states that single conductors or multiconductor cables that are installed without maintaining spacing must be derated. The NEC does not provide a prescriptive distance to be considered as “maintaining spacing.” If assemblies, such as MC cable, are run through the same space, there likely is some space between each of the cable assemblies unless they are bundled and tied together. As long as there is some space, there is room for air to circulate.


You are correct about the changes for the rooftop adders; the technical committee made significant revisions in 310.15(B)(3)(c).


Feed-through conductors


In the past, I have seen feeder-tapped panelboards that always had the feeder energized even though the tap-supplied panelboard could be de-energized. In an existing facility with an extremely small amount of room, we need to supply two 200-ampere panelboards. Can the feeder to one of the panelboards travel through the other? We cannot find it in the NEC.


Yes, there are prescriptive requirements that permit such an installation. The requirement you are referring to is located in Section 312.8. While your question deals with panelboards, the NEC answer is found in Article 312, which provides requirements for cabinets, cutout boxes and meter-socket enclosures. It is imperative to understand the Article 100 definition of a panelboard to find your answer. Panelboards “are designed to be placed in a cabinet or cutout box.” 


Section 312.8 permits enclosures that contain switches and overcurrent devices (panelboards) to contain conductors that feed through, are spliced in, or tapped off of other enclosures, switches or overcurrent devices under prescriptive conditions. The total of all conductors installed at any cross section cannot exceed 40 percent of the cross-sectional area of that space. Where splices and taps are installed, it cannot exceed 75 percent of the cross-sectional area of that space. 


Where conductors feed through a panelboard as you described in your question, a warning label complying with 110.21(B) must be applied on the enclosure (panelboard) that identifies the closest disconnecting means for any feed-through conductors. Section 110.21(B) states that this field-applied hazard marking must use appropriate words, colors and symbols of the hazard to adequately warn personnel. In addition, the marking must be permanently applied, not handwritten, and of sufficient durability to withstand the environment in which it is installed. This marking warns other installers and maintenance personnel of the hazard before they open an enclosure.


Workspace clearances and 70E


Why are the working space distances in 110.26 different from the arc flash boundary distances in NFPA 70E? In some cases, the working space is shorter, but, in others, the flash boundary is significantly higher. Are these two requirements correlated? Why doesn’t the NEC contain the arc flash boundaries and require those clearances on the initial installation?


Working space requirements in Section 110.26 are not associated with an arc flash boundary distance in NFPA 70E. The working space requirements in the NEC are simply a minimum amount of space necessary to permit ready and safe operation and maintenance of equipment that is likely to require examination, adjustment, servicing or maintenance while energized. These working space dimensions do not address arc flash boundaries.


A sample violation of working space clearances required by Section 110.26 is seen in small electrical closets where equipment, such as a small transformer, is installed in the working space in front of a panelboard. This represents a significant hazard for the installer/maintainer that must perform tasks such as troubleshooting in an energized panelboard. In this case, the worker would be leaning on a grounded transformer enclosure to perform tasks in an energized panelboard. The NEC contains installation requirements and NFPA 70E addresses safe electrical work practices. It is important to remember that the goal of NFPA 70E is to always eliminate the hazard by establishing an “electrically safe work condition.”


Listed holiday lighting


Each holiday season, we provide temporary power for decorative lighting at a large commercial facility. The installation is a very large display that lines driveways for the community to drive through and view. The maintenance personnel build much of the display in their shop. We understand that the NEC requires listed lighting fixtures and this issue comes up every year. Is there an exception for this type of lighting in the NEC?


No. Section 410.160 requires decorative lighting and similar holiday lighting accessories to be listed in accordance with Section 590.3(B). This permits decorative holiday lighting to be temporarily installed in accordance with Article 590 for not more than 90 days. In addition, Section 590.5 requires decorative holiday lighting installed as permitted in 590.3(B) to be listed.