Last Updated: 2026-10-06
Answer Capsule: An arc flash label lists the nominal system voltage, the arc flash boundary, either the incident energy at a working distance or the PPE category, and the date the assessment was completed. NFPA 70E-2024 Section 130.5(H) sets these fields. Read them in that order to pick your PPE, set your boundaries, and confirm the study is still current.
You open the electrical room door and the main switchboard has a label with eight lines of data on it. Read that label wrong and someone is either overdressed and slow, or underdressed and exposed. Print Pro AZ prints thousands of these labels a year. The most common question we get is not about the code. It is "what does this line actually mean?"
This guide shows you how to read arc flash labels one field at a time. We use sample values from a 480 V main switchboard, the kind on most commercial jobs in Phoenix. For each field you get the plain meaning, where the number comes from, and what to do with it. By the end you can glance at any label and know your boundaries, your PPE, and whether the study is still good.
What Does a Complete Arc Flash Label Look Like?
A complete arc flash label has a signal word, an equipment ID, and the four data items required by NFPA 70E-2024 Section 130.5(H). Most labels also add the two shock boundaries. Here are the sample values from the Print Pro AZ printed field guide.
WARNING Arc Flash and Shock Hazard. Appropriate PPE Required. Equipment ID: MSB-1 Nominal System Voltage: 480 VAC Arc Flash Boundary: 4 ft 6 in Incident Energy: 8.7 cal/cm2 at 18 in working distance Limited Approach Boundary: 3 ft 6 in Restricted Approach Boundary: 1 ft 0 in Assessment Completed: 08/12/2026
Two documents drive this layout. NFPA 70E 130.5(H) sets the data the label must carry in the workplace. The National Electrical Code, Section 110.16 in the 2026 edition, requires the same data label on non-dwelling service and feeder equipment at any amp rating. Both are covered in our arc flash labels NFPA 70E 2024 requirements guide.
Field 1: What Does Nominal System Voltage Tell You?
The nominal system voltage tells you the shock hazard and which row of the shock boundary tables applies. On the sample label it reads 480 VAC, the system voltage feeding MSB-1.
What to do with it: Use the voltage to pick your shock protection. Voltage-rated gloves and tools must match or exceed this number. The voltage also sets the limited and restricted approach boundaries from Table 130.4(E)(a). If the label does not match the nameplate on the gear, stop and ask before you open anything.
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A 2-page field card: the four items NEC 2026 now requires on every label, the PPE category table, the table-method disqualifiers, and the changes that force a relabel. Print it and keep it in the truck.
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Field 2: What Is the Arc Flash Boundary on the Label?
The arc flash boundary is the distance from the energized parts where incident energy drops to 1.2 cal/cm2. That is the point where a second-degree burn starts. On the sample label it is 4 ft 6 in.
Anyone inside that line during energized work needs arc-rated PPE. Outside it, only the shock boundaries apply.
What to do with it: Measure it out and mark it. Tape or cones at 4 ft 6 in keep helpers and other trades clear. If the boundary is bigger than the electrical room, the whole room is inside it.
Field 3: Incident Energy or PPE Category, Which One Is on Your Label?
Your label shows either the incident energy with a working distance or the arc flash PPE category, never both. NFPA 70E 130.5(G) lets the engineer choose one method per piece of equipment. Both on one label is one of the five inspection failures Print Pro AZ sees most often.
If your label shows incident energy, like the sample's 8.7 cal/cm2 at 18 in, read it as heat. That is what a worker receives at 18 inches from the arc. Working distance is commonly 18 inches for 600 V class equipment. Your clothing and face protection need an arc rating at or above 8.7 cal/cm2. An 8 cal/cm2 shirt does not cover it.
If your label shows a PPE category instead, use Table 130.7(C)(15)(c) to find the minimum arc rating:
- CAT 1: 4 cal/cm2
- CAT 2: 8 cal/cm2
- CAT 3: 25 cal/cm2
- CAT 4: 40 cal/cm2
Field note: Below 1.2 cal/cm2, NFPA 70E does not require arc-rated PPE for the arc flash hazard. Shock PPE still applies. A low number on the label does not mean bare hands.
Field 4: Why Does the Assessment Date Matter More Than the Print Date?
The assessment date matters because it starts the review clock. NFPA 70E 130.5(H) requires the data behind the label to be reviewed at intervals not to exceed 5 years. The date is the day the assessment was completed, not the day the label went on. On the sample it reads 08/12/2026.
What to do with it: If the date is more than 5 years old, treat the numbers as suspect and get the study reviewed. If the date is fresh but the facility added a generator, swapped breakers, or changed a transformer, the numbers may be stale anyway. Our post on the arc flash assessment date requirement covers what counts as a valid date.
What Are the Limited and Restricted Approach Boundaries?
The limited and restricted approach boundaries are shock boundaries, and they come from Table 130.4(E)(a) for AC systems, not from the arc flash calculation. On the sample label they are 3 ft 6 in and 1 ft 0 in.
- Limited approach boundary (3 ft 6 in): Unqualified persons stay outside this line unless a qualified person escorts them.
- Restricted approach boundary (1 ft 0 in): Only a qualified person with shock PPE and a documented plan crosses this line.
What to do with it: On this label the arc flash boundary (4 ft 6 in) is larger than the limited approach boundary (3 ft 6 in). That is common on 480 V gear. You reach the arc flash line first, so arc-rated PPE goes on first.
How Do You Read an Arc Flash Label in Under a Minute?
Brent Hanke, founder of Print Pro AZ, tells crews to read a label in the same order every time. Signal word, voltage, arc flash boundary, PPE number, date.
| Field | What It Means | What to Do With It |
|---|---|---|
| Signal word (WARNING) | ANSI Z535.4 hazard level chosen by the facility | Read it as "stop and check PPE" |
| Equipment ID (MSB-1) | Matches the one-line diagram and the study table | Confirm you are at the right gear |
| Nominal system voltage (480 VAC) | Shock hazard level | Pick voltage-rated gloves and tools |
| Arc flash boundary (4 ft 6 in) | Distance to 1.2 cal/cm2 | Mark it; arc-rated PPE inside |
| Incident energy (8.7 cal/cm2 at 18 in) | Heat at the working distance | Wear gear rated at or above this number |
| Limited approach (3 ft 6 in) | Shock boundary for unqualified persons | Keep helpers outside it |
| Restricted approach (1 ft 0 in) | Shock boundary for qualified persons | Shock PPE and a plan to cross |
| Assessment completed (08/12/2026) | Start of the 5-year review clock | Flag anything older than 5 years |
What Goes Wrong When a Crew Misreads the Label?
The most common misread is treating the incident energy number as a category number. Here is a call Print Pro AZ gets every month. A maintenance lead sees 8.7 cal/cm2, thinks "that is about CAT 2," and sends the crew in with 8 cal/cm2 shirts. The gear is rated below the label value. The safety audit catches it.
The fix is simple. If the label gives a number, match or beat the number. If it gives a category, match or beat the category minimum. Never convert one to the other in your head.
The other frequent problem is a label that cannot be read at all. Faded vinyl, a sticker inside the door, or a generic "ARC FLASH HAZARD" warning with no data all fail. Print Pro AZ prints arc flash labels on UV-rated polyester and .048 aluminum so the fields stay readable in an Arizona yard. Under NEC 2026, a generic sticker with no data no longer satisfies 110.16 once your state adopts the edition. OSHA enforces the workplace side through the General Duty Clause and points to NFPA 70E on its arc flash hazards page. Confirm which NEC edition your AHJ enforces.
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Frequently Asked Questions
What does cal/cm2 mean on an arc flash label?
Cal/cm2 is calories per square centimeter, a measure of heat energy landing on a surface. On an arc flash label it is the incident energy a worker would receive at the stated working distance. NFPA 70E uses 1.2 cal/cm2 as the onset of a second-degree burn, and that value sets the arc flash boundary.
Does an arc flash label tell me exactly what PPE to wear?
It tells you the minimum arc rating or the PPE category, not the specific garments. Your electrical safety program under NFPA 70E 110.3 maps the label value to clothing, face protection, and gloves.
What if my arc flash label has no assessment date?
Treat the label as incomplete. NFPA 70E 130.5(H) requires the data to be reviewed at intervals not to exceed 5 years, and you cannot check that without a date. Ask for the study report and print new labels with the completion date.
Can an arc flash label show both incident energy and a PPE category?
No. NFPA 70E 130.5(G) allows the incident energy analysis method or the PPE category method for a piece of equipment, not both. A label with both values fails inspection and should be replaced.
Conclusion
Three things to remember. First, every compliant label carries voltage, arc flash boundary, one PPE method, and the assessment date. Second, incident energy and PPE category are different measures, and your gear must match or beat whichever one the label shows. Third, the assessment date is the only way to know if the numbers are still good.
Reading the label right keeps your crew dressed correctly and keeps the inspector moving. If your labels are faded, generic, or missing a date, Print Pro AZ turns your study data into a full label set with same-week shipping.
Have switchgear to label? Send us your plan sets and we will build the set from your study. Questions? Call Brent: (602) 649-5305.
Sources
- NFPA 70E, Standard for Electrical Safety in the Workplace
- NFPA 70, National Electrical Code
- OSHA, Arc Flash Hazards
Brent Hanke | Print Pro AZ | (602) 649-5305 | b.hanke@printproaz.com
Brent Hanke is the founder of Print Pro AZ, supplying NEC-compliant labels to contractors across the country.