An arc flash label tells a qualified worker how dangerous a piece of electrical equipment could be if an arc flash happened while they were working on it energized, and what distances and protective equipment apply. The values come from an engineering study of that specific equipment. A label is only as good as the study behind it, and it is a starting point for planning work, not permission to do it.
Why labels exist
An arc flash is an explosive release of energy when current flows through air between conductors or to ground. It can cause severe burns, blast injuries, hearing damage and eye injuries, and it can happen in a fraction of a second. For background, see arc flash basics.
The severity depends on the available fault current, how quickly the protective device upstream clears the fault, the voltage, the equipment's construction and how far the worker is from the arc. These vary greatly from one piece of equipment to the next, even within the same building. A label puts the result of that analysis on the equipment, where the worker needs it. In Canada, CSA Z462 sets out workplace electrical safety requirements, including the risk assessment and equipment labelling. Provincial occupational health and safety rules set the legal duties, and they refer to or rely on Z462 in different ways. Check the current edition and your province's rules.
What is on the label
Label layouts differ, but most carry the same core information.
Equipment and nominal voltage
The label identifies the equipment by the same name used on the single-line diagram and in the study, such as a switchboard, panel or motor control centre. The voltage tells the worker which shock protection and tools apply.
Incident energy and working distance
Incident energy is the heat energy that would reach a worker's face and chest at a stated working distance, usually expressed in calories per square centimetre (cal/cm²). It is calculated using a recognized method, commonly IEEE 1584. The working distance matters: the same arc delivers much less energy at a greater distance, so the value only applies at the distance stated. Clothing and face protection must have an arc rating at least equal to the incident energy.
PPE category
Some labels show a PPE category instead of, or as well as, incident energy. Categories come from tables in CSA Z462 that apply only within stated limits of fault current and clearing time. A study-based incident energy is generally more specific. Labels should not mix the two methods in a way that contradicts itself, and the site's electrical safety program should say which approach it uses.
Arc flash boundary
The distance from the equipment at which the incident energy drops to a level where an unprotected person could expect a second-degree burn to be unlikely. Anyone inside this boundary while the hazard exists must wear arc-rated PPE. It can extend well beyond the reach of the worker, which affects where other people can stand.
Shock approach boundaries
Separate from arc flash, these deal with the risk of contact with exposed energized parts. The limited approach boundary is the distance unqualified persons must stay outside of unless escorted by a qualified person. The restricted approach boundary is closer, and only qualified persons with appropriate shock protection and a documented plan may cross it.
Study reference and date
This ties the label to the study that produced it. If the date is old, or the study cannot be found, the label may no longer be valid.
What a label does not tell you
- Whether the work needs to be done energized at all. Codes and Z462 expect equipment to be put in an electrically safe work condition unless de-energizing creates a greater hazard or is not feasible.
- Whether the worker is qualified for this equipment and task.
- Whether the equipment's condition is normal. Damaged, poorly maintained or missing covers change the risk.
- Whether settings have been changed since the study, which can change the incident energy dramatically.
The label is not a work permit. Energized work requires a risk assessment, a qualified worker, appropriate PPE and, under most programs, a documented energized work permit. If in doubt, de-energize, follow lockout procedures and verify the absence of voltage. See lockout and tagout.
Using a label to plan a task
Suppose an electrician needs to take voltage readings inside a panel to troubleshoot a fault. A sound planning sequence, under the site's electrical safety program, looks like this:
- Ask whether it must be energized. Troubleshooting is one of the tasks where some energized work may be justified, but the reason should be recorded.
- Check the label is current. Confirm the equipment name matches the drawings and the study date is within the review period.
- Read the incident energy and working distance. Select arc-rated clothing, face and hand protection rated for at least that value at that distance.
- Read the boundaries. Set up barriers or an attendant so that nobody without PPE enters the arc flash boundary, and so that unqualified persons stay outside the limited approach boundary.
- Check the equipment. Doors, covers and the condition of the gear should be normal. Signs of overheating or damage change the plan.
- Complete the permit and job briefing, then do the work with insulated tools and rated test equipment.
Common label problems
| Problem | Why it matters | What to do |
|---|---|---|
| No label | Workers cannot plan safely | Commission a study before energized work |
| Generic label with no values | Warns of the hazard but gives no basis for PPE | Replace with study-based labels |
| Old or faded label | Values may not reflect the current system | Review the study and relabel |
| Label after equipment changes | New breakers, settings or utility supply can change values | Update the study and labels |
| Name does not match the drawings | Workers cannot confirm which values apply | Align names across labels, drawings and study |
When labels must be reviewed
The arc flash risk assessment should be reviewed when the electrical system changes and at regular intervals even if nothing obvious has changed. CSA Z462 sets a maximum review interval; check the current edition for the figure. Triggers for an earlier review include a service upgrade, new switchgear, changed breaker settings, added generators or solar PV, and any notice from the utility that its supply has changed. See what happens in an arc flash study for how the values are produced.
How ehZee can help
Our arc flash studies and labelling service collects the equipment data, builds the system model, calculates the label values and produces labels that match your drawings. We also review existing labels and studies to see whether they still reflect the system you have.
Common questions
Can we print our own labels from a template?
Labels can be printed in-house, but the values on them must come from a study or an approach permitted by your electrical safety program. A template with guessed values gives a false sense of safety.
What does a very high incident energy on a label mean?
It may mean that no available PPE is adequate for energized work on that equipment. The usual response is to de-energize for any work, and to ask the engineer whether settings or equipment changes could reduce the value.
Do labels go on every panel?
Labels generally go on equipment likely to be examined, adjusted, serviced or maintained while energized, such as switchboards, panelboards, motor control centres and disconnects. Your study and program define the list.