CQD Spotlight features questions and answers from NECA and ELECTRICAL CONTRACTOR’s Code Question of the Day program.
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From the archives—June 20, 2023
It seems like every version of the Code expands the labeling requirements. Once again, the 2023 edition has added more arc flash labeling requirements. What is the difference between the arc flash labeling requirements in Section 110.16(A) and 110.16(B) and the labeling requirements from NFPA 70E?
This is a great question. Two (2) labels pertaining to arc flash will be required for certain electrical equipment.
Section 110.16(A): Applies to various electrical equipment installed in other than dwelling units, that is likely to require adjustment, examination, servicing or maintenance while energized. This required field-marked or factory-installed label is intended to serve as a general warning to the qualified person of a potential arc flash hazard.
Section 110.16(B): This label is in addition to the one required in Section 110.16(A) and applies to service and feeder equipment rated 1,000A or more, in other than dwelling units. This label shall meet applicable industry standards like NFPA 70E, providing the necessary arc flash hazard assessment information and include the date the label was applied.
From the archives—July 15, 2024
Does an increase in distance from the source breaker to the equipment/load increase incident energy related to the arc flash hazard? Does an increase in distance from the secondary side of a transformer decrease the incident energy?
There are several factors that impact the available incident energy including the available fault current and the clearing time of the OCPD.
A longer distance from the source to the equipment/load may result in a lower available fault current; however, a lower available fault-current may result in the OCPD taking more time to operate/open. Therefore, a larger distance does not always equate to lower incident energy.
2024 NFPA 70E, Section 130.5(C), Informational Note No. 3 provides information on this topic. Additionally, Informational Annex D of NFPA 70E provides guidance on the methods for calculating incident energy.
Another consideration is also Section and Table 725.144, which provides additional requirements for the transmission of power and data.
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Post sponsored by Eaton Corp.
The recent NECA Code Questions of the Day raise important points about arc flash labeling under NEC 110.16(A) and (B), and about how distance and system configuration affect incident energy. From Eaton’s standpoint, the most critical factor in both discussions is available fault current, because it directly influences arcing current and, ultimately, the clearing time of the upstream overcurrent protective device. Incident energy is fundamentally a product of energy release over time, so even a system with lower fault current can produce higher incident energy if the OCPD takes longer to operate.
A key part of determining available fault current is understanding the impedance of the electrical system, and that requires an accurate, up-to-date single-line diagram. This is one of the most overlooked elements in arc flash studies. Without a trustworthy single-line, results for fault current, arcing current and PPE selection may all be incorrect.
The NEC requirement to mark maximum available fault current is intended to support proper application of equipment interrupting ratings and short-circuit current ratings. However, using that same maximum value in an arc flash assessment requires engineering judgment. Maximum fault current does not always produce the highest incident energy, because higher arcing current may cause the device to clear faster. NFPA 70E Annex D and 130.5(C) informational notes explain this clearly. The maximum value can be used with the PPE category method, but for calculated incident energy it may not be conservative.
Eaton’s engineering services support facilities by calculating fault current, modeling impedance, analyzing clearing times and producing accurate arc flash labels compliant with NEC 110.16 and NFPA 70E.
Finally, while arc flash labels are typically field-applied, it is not impossible for equipment to be labeled at the factory. With the right parameters known, available fault current and upstream OCPD trip characteristics, an argument could be made that a maximum incident energy could be determined for all fault currents up to upstream OCPDs interrupting rating.
