The arc flash label is the notice fixed on panelboards, switchgear and motor control centers that tells the worker how much arc risk there is and what protection is needed. NFPA 70E requires the nominal voltage, the arc flash boundary and at least one protection datum: the incident energy with its working distance or the PPE category (not both), the minimum arc rating of clothing, or the site-specific PPE level. The data comes from an arc flash study, and the label loses validity when the settings or the network change.
What the label is for
An electrician who is about to open an energized panel to measure, operate or inspect needs to know two things before getting close: how far the hazard reaches if an arc forms and what protection must be worn. The arc flash label tells them at the equipment door, without having to look up the study.
The label is not a generic «danger» sticker. Each one corresponds to a specific piece of equipment and a specific calculation: the short-circuit current at that point, the protective device that clears the fault and its time, the equipment configuration and the working distance. If any of these data changes, the label is out of date. That is why it can only come from an arc flash study.
What it must say under NFPA 70E
NFPA 70E (2024 edition) requires labeling electrical equipment, such as panelboards, switchgear and motor control centers, that may require examination, adjustment, servicing or maintenance while energized. The label must include:
| Item | Required | Comment |
|---|---|---|
| Nominal system voltage | Yes | It also defines the shock approach boundaries |
| Arc flash boundary | Yes | Distance at which incident energy drops to 1.2 cal/cm² |
| Incident energy with its working distance, or PPE category | At least one of the three protection items | Never both methods at once |
| Minimum arc rating of clothing | Alternative to the previous one | |
| Site-specific PPE level | When the company defines its own levels |
In supervised industrial installations where only qualified persons operate and maintain the system, the standard allows this information to be documented by other means accessible to the worker. In addition, the calculation method and the data supporting it must be documented and reviewed at intervals not exceeding five years.
PPE categories and how they are chosen are covered in arc flash PPE categories.
The NEC and factory labels
The NEC (NFPA 70), which governs installations in the United States and is adopted in several other countries, requires in its section 110.16 an arc flash warning marking on equipment. The 2026 edition extended the requirement to all service and feeder equipment in installations other than dwellings. It asks that the marking include the nominal voltage, the arc flash boundary, the available incident energy or the minimum PPE level, and the date the assessment was completed. Check which NEC edition each jurisdiction has adopted.
Other jurisdictions have their own rules for work on or near energized parts; the label content is usually taken from NFPA 70E, with the adaptation to the local code and the utility’s requirements that the client gives us. For example, in Mexico, NOM-029-STPS-2011 requires the risk analysis and protective equipment for electrical maintenance work. See NOM-029-STPS.
Where the data comes from
- Network model. Real single-line diagram, short-circuit level and equipment data
- Real settings. Those loaded in relays, trip units and fuses
- IEEE 1584 calculation. Arcing current, clearing time and incident energy
- Review. High values, operating scenarios and mitigation
- Label. Data per equipment, ready to print
Common mistakes that make a label useless:
- Settings from the drawing and not from the relay. If the study used a setting different from the one loaded, the real energy can be much higher.
- A single scenario. With the emergency generator or with minimum grid, the arcing current is lower and the protection may take longer. The label must reflect the worst case.
- A generic label per panel type, copied from other equipment.
- Line side of the main breaker forgotten: there the fault is cleared by the protection on the transformer primary, much slower.
- Old labels after a change of transformer, settings or the short-circuit level supplied by the utility.
How far the calculation backs the printed number
The label value comes from a model with limits. According to the presentation material on the 2018 edition of IEEE 1584 (IEEE PES/IAS Alberta chapter; the authors’ interpretation, not the text of the standard) and the technical sources consulted:
- The model covers three-phase AC systems from 208 V to 15 kV, at 50 or 60 Hz. Single-phase and DC systems are outside it, although the guide offers guidance and references for them.
- The application limits of the model are given by voltage range: from 208 V to 600 V, bolted fault current of 0.5 to 106 kA; from 600 V to 15 kV, 0.2 to 65 kA. Equipment outside that range needs another method, which according to the same source the user must investigate and justify.
- The model distinguishes five electrode configurations (VOA, VCB, VCBB, HOA and HCB). One piece of equipment can combine several, and each can give a different energy.
- The standard does not recommend PPE: it gives the incident energy and the arc flash boundary. Translating that into a category or clothing is a later step in NFPA 70E or company policy.
A practical note for imported equipment: the German guide DGUV Information 203-077 expresses exposure in kJ/m² and gives the equivalence 1 cal/cm² = 41.868 kJ/m². With it, the 1.2 cal/cm² limit of the arc flash boundary equals about 50 kJ/m², useful for reading documentation of European origin.
How to read a label
For the worker, the label answers three questions in this order:
- How far does the hazard reach? The arc flash boundary marks the distance beyond which arc-rated clothing is needed. Closer than that, without adequate protection, no one enters.
- What protection do I need? The incident energy is compared with the arc rating of the available clothing: the clothing must have an equal or higher rating. If the label shows a PPE category, the kit for that category is used.
- What voltage is the equipment at? It defines the shock approach boundaries and the insulated gloves and tools.
If the incident energy on the label is higher than that of any available PPE, the message is clear: that equipment is not worked on energized.
When to replace the labels
- When changing protection settings, transformers, cables or the network configuration.
- When the utility reports a new short-circuit level at the point of connection.
- When installing on-site generation, which contributes fault current.
- In the periodic review of the risk assessment, not exceeding five years per NFPA 70E.
If the energy turns out to be high, before printing it is worth reviewing the options to lower it. See how to reduce incident energy. The measure that reduces it most is shortening the clearing time, for example with arc flash protection by light detection.
We do your study and your labels
Our team performs the arc flash study with IEEE 1584 on the real settings of your relays, which we read from each device, and delivers the table per equipment and the labels ready to print. We work remotely worldwide, and field data collection in Colombia or elsewhere on request. See our engineering design and studies service and write to us through the contact page.
Related guides
- Arc flash study: IEEE 1584 and NFPA 70E
- Arc flash PPE categories
- How to reduce incident energy
- Short-circuit study
- Low-voltage panelboard and MCC
- Arc flash relay: protection by light detection
References
- NFPA 70E, Standard for Electrical Safety in the Workplace, 2024 edition (equipment labeling and arc flash risk assessment).
- NFPA 70, National Electrical Code, section 110.16.
- Mohla and Lee, Introduction to the 2018 Edition of IEEE 1584 (presentation, IEEE PES/IAS Alberta chapter, 2019); DGUV Information 203-077 (2020, in German).
- IEEE 1584-2018, IEEE Guide for Performing Arc-Flash Hazard Calculations.
- NOM-029-STPS-2011, Maintenance of electrical installations in workplaces - Safety conditions.
Frequently asked questions
What information must an arc flash label have under NFPA 70E?
The nominal system voltage, the arc flash boundary and at least one of these: the available incident energy with its working distance, or the equipment's PPE category (but not both); the minimum arc rating of clothing; or the site-specific PPE level.
Can I put both the incident energy and the PPE category on the same label?
No. NFPA 70E asks for one or the other, because they are two different methods: incident energy comes from the analysis of each piece of equipment, and the category comes from the standard's tables, which are only valid within their current and time limits. Mixing them can lead to choosing the wrong protection.
How often are arc flash labels updated?
NFPA 70E requires reviewing the arc flash risk assessment at intervals not exceeding five years and whenever a modification changes the risk: changes of settings, transformer, network short-circuit level or topology. If the study changes, the label changes.