Key takeaways
- NEC 110.16 calls for arc flash warning labels on equipment that is likely to be worked on while energized.
- The figures on a detailed label come from an arc flash study, which is engineering work done by a qualified engineer.
- Wattsmith installs the labels the study produces and keeps the equipment as the study modeled it.
- Equipment changes can make a study out of date, so changes are flagged for the engineer to update it.
Arc flash labels are the warnings on switchboards, panelboards, control panels and other equipment that tell a worker what hazard waits behind the cover. In an industrial plant they are a code requirement and a daily safety tool. This guide explains what the labels are, which equipment needs them, who determines the figures printed on them, and how we install them from your engineer's study and keep them accurate as the plant changes.
What are arc flash labels and why does equipment need them?
Arc flash labels are warnings placed on electrical equipment that may be worked on while energized. NEC 110.16 calls for them so that anyone opening the equipment knows an arc flash hazard exists. A detailed label also carries the figures from an arc flash study, which guide the protective equipment and work practices used.
An arc flash is the release of energy when current jumps through the air between conductors or to ground. It produces intense heat, light and pressure in a fraction of a second. It can start from a dropped tool, a loose connection, corrosion or a failed part. The label does not prevent an arc. It tells the person in front of the equipment that the hazard is there, so they plan the work, de-energize where they can, and wear the right protection where they cannot.
Labeling is listed with our other plant services on the industrial electrical contractor page.
Who determines the figures on an arc flash label?
A qualified engineer does. The figures on a detailed label come from an arc flash study, which is engineering work based on the plant's distribution, the utility's available fault current and the settings of the protective devices. Wattsmith does not perform the study. We install the labels the study produces, exactly as the engineer issued them.
The study models the electrical system as it is: the service, the transformers, the conductors, the breakers and fuses and how they are set. From that model, the engineer produces the label content for each piece of equipment. That is why the study and the labels are tied to the equipment as it stands. Change a breaker setting or swap a transformer and the model no longer matches the plant.
Our part sits on both sides of the study. Before it, we can help the engineer by opening equipment safely so nameplates and settings can be recorded. After it, we install the labels and keep the equipment as the study modeled it.
Keeping those roles separate protects you. A label with figures that did not come from a study gives a worker false confidence, which is worse than a plain warning. If no study exists yet, the right first step is to engage a qualified engineer, and we can tell you what information the engineer will likely ask for, such as the utility's fault current data, transformer nameplates and breaker settings. Gathering that information safely is electrical work we can do. Turning it into incident energy figures and label content is engineering work, and it stays with the engineer.
Which equipment needs arc flash labels?
NEC 110.16 applies to equipment that is likely to be examined, adjusted, serviced or maintained while energized, such as switchboards, panelboards, industrial control panels, meter socket enclosures and motor control centers. In a plant that covers most of the distribution and control equipment people open during a normal working week.
The engineer's study usually lists every piece of equipment it modeled and the label for each. That list becomes our install list. Where we find equipment in the field that the study did not include, such as a panel added after the study was done, we flag it to you and the engineer instead of guessing at a label for it.
How are arc flash labels installed from the engineer's study?
We match each label to the equipment the study names, confirm the equipment in the field matches what the study modeled, and place the label where it is clearly visible to a person before they open or work on the equipment. Any mismatch between the field and the study goes back to the engineer before that label goes up.
In practice the work runs panel by panel. We check the equipment name and location against the study, look for anything that has obviously changed, such as a different breaker or a replaced transformer, and place the label on the outside of the equipment where it will be read. The labels themselves are durable, made to stay legible in the environment where they hang, including hot or dusty areas and washdown floors.
At the end, you get a list of what was labeled, what was flagged and why. That record is what lets the next change be handled cleanly.
When should an arc flash study be updated?
Whenever the system the study modeled changes in a way that could change the hazard: a new or replaced transformer, a service change, new feeders, different breakers or fuses, changed trip settings, or a change in the utility's available fault current. The engineer decides whether an update is needed; we flag the change.
This is where the electrical contractor's role matters most. We are the ones in the equipment when it changes. When a job of ours changes something the study modeled, the job record says so and you are told, so the engineer can review it and issue revised labels. A study that is never updated slowly drifts away from the plant it describes, and its labels drift with it.
Service and transformer changes are covered in our guide to 480 volt distribution and transformers, and most of them are exactly the kind of change that should go back to the engineer.
Do arc flash labels change how electricians work on equipment?
Yes. The label tells a qualified worker the hazard before the cover comes off, so the work is planned around it. The first choice is to de-energize and lock out the equipment. Where energized work is truly needed, the label's figures guide the protective equipment and boundaries used under the plant's safety program.
Electrical safety in the workplace is covered by NFPA 70E, and most plants build their electrical safety program around it. Energized checks such as infrared scans and load readings follow those safe work practices. The label is one part of that program, along with training, lockout procedures and the right equipment for the task.
Many label problems are found during routine checks, which is one reason labels are part of our industrial electrical maintenance program.
What goes wrong with arc flash labels, and how is it prevented?
Labels fade, get painted over or end up on the wrong equipment, and studies go stale as the plant changes around them. Installing durable labels from the study, checking them on every maintenance visit and flagging each equipment change to the engineer keep the labels matched to the plant people actually work in.
- Install each label from the engineer's study, matched to the equipment it names.
- Flag equipment that the study did not include instead of guessing at a label.
- Check that labels are present and legible on each maintenance visit.
- Record every change to modeled equipment and send it to the engineer.
When a repair changes equipment the study modeled, our electrical repair work notes it for the engineer. For our wider scope, see commercial electrical services. If you have a study and need the labels installed, or equipment has changed since the study was done, reach us through our contact page.