How to Read an Arc Flash Label, Field by Field

An arc-flash label is a field summary of an assessment, not permission to perform energized work. Read the method, working distance, dates, and traceability information together; a large number without its conditions can be misleading.

Last reviewed: July 19, 2026.

1. Signal word

WARNING and DANGER are hazard-communication signal words. Their selection should follow the equipment owner’s documented ANSI Z535-style policy and hazard assessment. IEEE 1584 does not create a universal “DANGER at 40 cal/cm²” rule.

Labels generated by this tool use WARNING by default. A site-specific signal-word policy must be reviewed separately before changing that behavior.

2. Nominal voltage

The equipment’s nominal AC system voltage. This drives shock boundaries and determines which calculation or table limits apply. It does not, by itself, tell you the incident energy.

3. Incident energy and working distance

Calculated labels show the estimated thermal exposure in cal/cm² at a stated working distance. The distance is part of the result: 6.2 cal/cm² at 18 inches is not interchangeable with 6.2 cal/cm² at another distance.

Under the incident-energy method, the selected clothing system’s arc rating must meet or exceed the estimated incident energy. A qualified person still selects the complete head, face, hearing, hand, body, and shock protection appropriate to the task.

4. Arc-flash boundary

The distance at which the modeled incident energy falls to 1.2 cal/cm². People crossing that boundary during a potential arc-flash exposure need the protection and work controls established by the risk assessment. See arc-flash boundary explained for the calculation context.

5. PPE selection basis

This field tells you which NFPA 70E method produced the result:

• Incident-energy analysis: the label prints the calculated incident energy and a minimum arc-rating requirement. It does not print a PPE category.
• PPE category method: the label prints the category assigned by the applicable task/equipment table after its limits were checked. It does not invent an incident-energy number.

Do not convert calculated energy into a category. The two methods are alternatives for the same equipment.

6. Available fault current and date

The bolted fault-current value used by the assessment, ideally with the date it was obtained. Utility changes, transformer replacements, conductor changes, or generator additions can make this input stale.

Higher fault current does not always mean a higher arc-flash result. A higher current may make the protective device trip faster, so both current and clearing time must be evaluated together.

7. Assessment date, report and label ID

These fields connect the door label to the stored calculation record. Use them to verify the equipment identity, input sources, engine version, protective-device clearing times, and whether the assessment still matches the installation.

8. Scope and warning notes

Read every note. Important examples include a reduced-arcing-current case governing, a working-distance model floor, a table method being unavailable, or enclosure dimensions having been assumed.

If a label says engineering study required, it is not a lower-risk result. It means the software did not have a verified applicable method and deliberately withheld a category or boundary.

Before relying on the label

1. Confirm the equipment ID and location.
2. Confirm the assessment still matches the one-line diagram and protective-device settings.
3. Check the method and PPE-selection basis.
4. Verify the stated working distance matches the task.
5. Confirm available fault current and clearing-time sources.
6. Have a qualified person complete the task-specific risk assessment and energized-work justification.

You can inspect the full input and intermediate-value record in the free calculator preview. For field requirements, see arc-flash label requirements.