Arc Flash Labeling Under NEC 2026: What §110.16 Means for Your Facility

For more than twenty years, most of the electrical equipment in a commercial or industrial building carried the same arc flash label: a yellow and black sticker that said WARNING, Arc Flash Hazard, and little else. It satisfied the Code. It told a qualified electrician nothing about how much energy would come out of that panel if something went wrong, how far away they needed to stand, or what to wear.

The 2026 edition of the National Electrical Code ends that arrangement. Section 110.16 has been rewritten, and the generic sticker is gone.

What the 2023 rule actually required

Under NEC 2023, §110.16 worked in two tiers.¹ Subsection (A) required a field or factory applied marking on switchboards, switchgear, enclosed panelboards, industrial control panels, meter socket enclosures, and motor control centers in other than dwelling units, warning qualified persons of the potential arc flash hazard. It did not require any numbers. Subsection (B) went further, but only for service equipment and feeder-supplied equipment rated 1000 amperes or more (the 2017 and 2020 editions had set that line at 1200 amperes and service equipment only): those pieces needed a permanent arc flash label in accordance with applicable industry practice, meaning NFPA 70E, including the date the label was applied.

In practice, the 1000 ampere line meant that the main switchboard got a real label and everything downstream of it got a sticker. A 400 ampere distribution panel feeding a production floor, a motor control center running a pump house, an industrial control panel on a compressor skid: all of them carried a warning that warned of nothing in particular.

What NEC 2026 says

The 2026 text collapses the two tiers into one requirement and drops the ampere threshold entirely.² In other than dwelling units, a permanent arc flash marking must be field or factory applied to service equipment and feeder-supplied equipment such as switchboards, switchgear, enclosed panelboards, industrial control panels, meter socket enclosures, and motor control centers that are likely to require examination, adjustment, servicing, or maintenance while energized.

Two things about that sentence deserve attention. The equipment list is introduced with "such as," which means it is illustrative, not exhaustive. And the qualifier is whether the equipment is likely to be worked on while energized, not how big it is. A 100 ampere panel that a technician opens to troubleshoot a live circuit is inside the rule.

The marking must comply with §110.21(B), the general rule for field-applied hazard markings: it has to adequately warn of the hazard, be permanently affixed and not handwritten, and be durable enough for the environment.³ It must be clearly visible to qualified persons before they examine, adjust, service, or maintain the equipment. And it must include four items:

1. The nominal system voltage.
2. The arc flash boundary.
3. The available incident energy or the minimum required level of personal protective equipment.
4. The date the assessment was completed.

Compare that to the 2023 version. Where the old rule deferred to "applicable industry practice" and left the electrician to work out what that meant, the new rule names the four items and puts them in the Code itself. And the date is no longer the date the label was applied. It is the date the assessment was completed. That distinction changes the character of the label.

Why the date matters

An arc flash label is the output of an engineering calculation. That calculation depends on the available fault current from the utility, the impedance of the transformers and conductors between the utility and the equipment, and the clearing time of the overcurrent device protecting it. Change any of those and the incident energy changes. Utilities upgrade transformers. Facilities add a generator, replace a breaker with a different trip unit, or reconfigure a distribution board. The label stays on the door, unchanged, and quietly becomes wrong.

NFPA 70E, the workplace electrical safety standard that employers are already held to, has addressed this for years. Section 130.5(G) requires the incident energy analysis to be updated when changes occur in the distribution system that could affect the results, and reviewed for accuracy at intervals not to exceed five years.⁴ Until now, nothing on the label itself told anyone when that clock started. The 2026 NEC puts the date on the door. An inspector, a maintenance electrician, or a contractor bidding a modification can read it and know immediately whether the label is current or overdue for review.

The Code also aligns the label content with NFPA 70E-2024 Section 130.5(H), which lists what an equipment label must carry.⁴ The NEC and 70E were written by different committees for different audiences, and for years the installation code lagged the workplace standard. The 2026 language closes most of that gap.

What this means for a facility

The consequence that matters most is this: you cannot produce the four required items without an arc flash study, or without a defensible application of the NFPA 70E table method, which has its own limits. The tables in 70E can only be used when the available fault current and the clearing time of the protective device are within the parameters the tables assume. Once a facility has equipment that falls outside those parameters, and most industrial facilities do somewhere in their distribution system, the incident energy has to be calculated.

Under the 2023 Code, that study was a workplace safety obligation under 70E, enforceable by OSHA after the fact. Under the 2026 Code, the label that depends on it is an installation requirement, verified by the electrical inspector before the work is signed off. Labeling has moved from a recommendation that a good facility followed to a condition of passing inspection.

A few practical points follow from that.

The requirement is not retroactive. The NEC applies to new installations and to work performed under a permit after the edition is adopted in your jurisdiction. Existing equipment does not have to be relabeled because the Code changed. But the moment that equipment is modified, extended, or replaced under the new edition, the new label is part of the job.

The requirement does fall on the factory as well as the field. The text says field or factory applied. A panel builder can ship equipment with a compliant label if the engineering data exists at the time of manufacture, which it usually does not, because the available fault current at the installation is not known in the shop. In most cases the label will be applied in the field by whoever holds the study.

And the requirement is coming to Washington on a known schedule. Washington currently enforces the 2023 NEC. The Department of Labor and Industries opened rulemaking to adopt the 2026 edition on December 16, 2025, filed proposed rules in August 2026, and, if adopted as proposed, will put the 2026 edition into effect on December 31, 2026.⁵ Minnesota has already adopted the 2026 edition, effective August 17, 2026.⁶ Other states will follow on their own cycles.

What to do before your inspector does

If you manage a facility, three questions answer most of this.

Do you have an arc flash study? If so, when was it completed, and has anything changed in the distribution system since? A study older than five years, or one that predates a service upgrade or generator addition, does not meet the 70E review requirement today and will not produce a defensible date on a 2026 label.

Which equipment in your facility is likely to be worked on energized? That is the scope of the new rule. Panels that are only ever operated with the door closed and the power off are a smaller problem. Motor control centers, industrial control panels, and distribution panels where technicians troubleshoot live are the equipment the Code is describing.

Who owns the labels? A label is only as good as the calculation behind it and the record of when that calculation was done. Someone in the organization should be able to point to the study, the one-line diagram it was based on, and the date, for every label on every door.

MD Engineering performs arc flash and short-circuit studies, produces the labels that result from them, and maintains the documentation that supports them. If your last study is more than five years old or your facility has changed since it was done, the 2026 Code has just given you a deadline. Use it.