Many facilities treat an arc flash study as something done every five years and then set aside. The standard asks for more than that, and you can screen your study against NFPA 70E review triggers to see where yours stands.
A five year review has two jobs. It identifies what has changed in the system, and it verifies that the previous study’s findings were actually resolved. A study date, a set of labels, or a record of completed corrections does not, by itself, establish either one.
The Five Year Rule
NFPA 70E requires the incident energy analysis to be updated when changes occur in the electrical distribution system that could affect the results of the analysis, and to be reviewed for accuracy at intervals not exceeding five years.
Read that in order. The change trigger comes first. The five year interval is the backstop.
If your system changes in year two, the affected results need review in year two. The calendar does not defer that.
A review is not automatically a full recalculation. Its purpose is to determine whether the existing analysis is still accurate, needs targeted updates, or needs to be rebuilt.
What Triggers a Review
The following changes can affect available fault current, protective device clearing time, or both. When one occurs, the results for the affected equipment need to be reviewed.
Utility service changes. A utility transformer replacement or system change can alter available fault current at your service and at downstream equipment. These changes are not always communicated to the facility. We covered this in why a utility upgrade can make your arc flash labels wrong.
Transformer replacement. A transformer with a different rating or impedance changes fault current at the equipment it serves.
Breaker or fuse changes. A replacement device can have different time current characteristics or current limiting behavior than the device it replaced, even when the ampere rating matches.
Protective device setting changes. Adjustments to long-time, short-time, or instantaneous settings can change clearing time and incident energy without any hardware being replaced.
New equipment or added loads. New panels, MCCs, conductors, or distribution changes can alter the system. Putting existing spare capacity into service can also be a relevant change, even though no new equipment was purchased.
Generator or alternate source additions. These add fault current contributions and operating configurations that need to be evaluated.
These are among the first things we look for on a review, and they account for many of the problems we commonly find in existing arc flash studies.
A Low Number on the Label Does Not Establish Equipment Adequacy
On a recent five year review, we evaluated a group of low voltage panels whose labels reported low incident energy and a short arc flash boundary. By the label alone, they appeared to be among the least hazardous equipment in the building.
The prior study had also identified branch breakers in those panels whose interrupting ratings were below the available fault current at that location.
The prior findings had been marked corrected. Our review still needed to verify whether the installed changes actually resolved the equipment-rating deficiencies. A record of completed work is not, by itself, proof that the correction was technically adequate.
Incident energy and equipment ratings are separate evaluations. The study reported low incident energy. Confirming that result requires checking the installed protective devices, the calculated arcing current, the clearing characteristics of the device expected to interrupt the arc, and the analysis method used. A current-limiting fuse provides its fastest clearing only when the arcing current is high enough to fall in its current-limiting range. At lower arcing currents, clearing time can be considerably longer, and the incident energy result changes with it.
A low calculated incident energy value also does not establish that a breaker’s interrupting rating, or an assembly’s short-circuit current rating, is adequate for the available fault current. When a device is applied beyond its rating, there is no established basis for relying on it to interrupt a fault safely. The arc flash label does not communicate that condition. It was not designed to.
Series Ratings Need a Documented Basis
A downstream breaker with an interrupting rating below the available fault current may be acceptable when it is part of a valid series-rated combination with an upstream device. An upstream fuse’s high interrupting rating does not, by itself, establish the rating of the downstream breaker or assembly.
The NEC recognizes two paths. A tested combination relies on the manufacturer’s listed series ratings for the specific line-side device and load-side breaker, and the equipment must be marked accordingly. For existing installations, the NEC also permits a series combination selected under engineering supervision, with its own documentation, stamping, and field marking requirements. Both paths are subject to limits on motor contribution between the two devices, and both must apply to the equipment and conditions actually installed.
Fuse replacements deserve particular attention here. Corresponding Class RK1 and Class RK5 fuses can fit the same holders despite having different protective characteristics. Physical fit does not establish electrical suitability or a valid series rating. They have different current limiting characteristics. A listed combination identifies the fuse class and rating it was tested with, and a substitution must be checked against that listing rather than assumed to carry the same rating. The same substitution can also change the clearing time used in the incident energy calculation.
What a Five Year Review Re-Examines
A proper review is not only a search for what changed. It is also a second look at what the last study assumed, recommended, and reported as resolved.
Were prior recommendations implemented, and do they work? A previous study may have recommended a device change, a settings change, or a series-rated solution. If the work was recorded as complete, we verify the installed device, its ratings and settings, and the engineering basis for closing the finding.
Are the assumptions still assumptions? Studies sometimes carry devices as unidentified because equipment could not be de-energized or opened during field work. Those placeholders can survive later updates unless someone goes back and verifies them.
Do the modeled devices match what is installed? Replacement fuses and breakers that look equivalent may not be. The study inputs should reflect the devices that are in the equipment today.
Do the labels match the current assessment? NFPA 70E does not permit both PPE selection methods, the arc flash PPE category method and the incident energy analysis method, to be used on the same piece of equipment. When an assessment changes the method or the results for a piece of equipment, labels that are superseded or that conflict with the current assessment need to be removed or replaced, not supplemented.
What Happens If You Do Not Update
The labels on your equipment reflect the study that was done, not necessarily the system that exists today.
If the system has changed, a label’s incident energy value can understate or overstate actual exposure. Workers select PPE from that information, so its accuracy matters.
An outdated study can also leave miscoordinated protective devices or underrated equipment unidentified, and those conditions may come to light during an inspection or audit rather than on your own schedule.
How to Tell If Your Study Is Still Valid
Start with a few questions.
Has it been more than five years since the last study or review? If yes, a review is due.
Has the electrical system changed since the last study? If that cannot be answered clearly, a review should establish it.
Does the one line diagram match what is actually installed?
Were the last study’s findings closed out with verification? Pull the recommendations section of your existing report and check each item against what is installed and how it was documented as resolved.
Can each label be traced to the current assessment? Assessment-date labeling requirements under the 2026 NEC depend on the edition adopted in your jurisdiction and the equipment covered. Where a label has no traceable assessment date, that is a reason to investigate.
If a new study is likely, it helps to know the range up front. You can estimate it with our arc flash study cost estimator or see what drives arc flash study cost.
The Bottom Line
The five year interval is a backstop. System changes are triggers to review the affected results, whenever they occur.
A review also has to look backward. Before a previous finding is carried forward as resolved, verify the engineering basis for the correction and the condition of the equipment actually installed. A completed work record shows that something was done. Verification shows whether it solved the problem.
Need to Review Your Study?
If you are not sure your study reflects your current system, or whether the last set of findings was verified as resolved, that is where we start.