How to Read an Arc Flash Label

What the label is required to say

NFPA 70E sets the required contents of the label at 130.5(H). Equipment covered by that section must be marked with a label containing all of the following:

1. Nominal system voltage
2. Arc flash boundary
3. At least one of:
   • available incident energy and the corresponding working distance, or the arc flash PPE category from Table 130.7(C)(15)(a) or Table 130.7(C)(15)(b) — but not both;
   • minimum arc rating of clothing; or
   • site-specific level of PPE.

Two things follow immediately, and both catch people out. The first is that a label carrying only a category is still a compliant label — it is not a shortcut or a lesser version. The second is that the third field is a menu, not a fixed format, which is why the label on your switchgear can look nothing like the one at the plant down the road and both can be correct.

Nominal system voltage

The voltage the equipment operates at, phase to phase. It is the field people skip because they think they already know it, and it is worth reading anyway: in older facilities the label is occasionally the only place the as-built voltage was ever written down after a service change.

Voltage also drives the shock side of the job, which the arc flash label does not cover. The limited and restricted approach boundaries come from the shock risk assessment and the approach-distance table, not from this label. Two separate assessments, two separate sets of boundaries — see limited and restricted approach boundaries.

Arc flash boundary

The arc flash boundary is a distance. Cross it while the equipment is in a condition where an arc flash is possible and you need arc-rated protection, whoever you are and whatever you came to do. It applies to the electrician with the meter and to the manager standing behind them.

This is the field most often treated as advisory and it is the one with the clearest line in it. Outside the boundary, no arc-rated PPE is required for the arc flash hazard. Inside it, PPE is required. There is no partial credit for standing near the edge. More on how the distance is derived: the arc flash boundary explained.

The third field, and why yours differs from the next plant's

The third required element has three permitted forms, and which one you see tells you how the facility approached the problem.

Available incident energy and working distance means someone ran an incident energy analysis. This is the most informative label: it gives you a number in cal/cm² at a stated distance, and it lets you select PPE by arc rating rather than by category.

An arc flash PPE category means the facility used the table method instead. Categories come from Table 130.7(C)(15)(a) or Table 130.7(C)(15)(b), and those tables sit at 130.7(C)(15) in both the 2024 and the 2027 editions — the PPE tables did not renumber for 2027, whatever a 2024-era document may have told you.

Minimum arc rating of clothing or site-specific level of PPE are the remaining two forms. Both are compliant. Both put more of the interpretation on the facility's own written program, which means that if this is what your labels say, the label alone will not tell you what to wear — the electrical safety program has to.

Incident energy or PPE category — never both

The standard is explicit that a label may carry the incident energy figure or a category from the selection tables, but not both. This is not a formatting preference. The two are different methods of arriving at protection, and printing both invites a worker to mix them — to read a category off the label and then defend a lower arc rating using the incident energy number, or the reverse.

There is a related prohibition worth knowing: an incident energy result must not be used to pick a category out of the PPE-content table at 130.7(C)(15)(c). If you have a calculated incident energy, you select PPE by arc rating against that number. You do not convert it into a category and then look the category up.

If you are looking at a label that carries both, that is a finding. It usually means two studies at different times, or a template that was filled in by someone working from the wrong method.

Working distance: the number people misread

Where a label states incident energy, it must state the working distance that goes with it — and the pairing is the whole point. An incident energy figure without its working distance is meaningless, because incident energy falls off sharply with distance.

The practical error is assuming the stated distance describes where you will be standing. It describes where the calculation was evaluated, typically at the torso of a person doing that task. Get closer than the stated distance and the energy at your body is higher than the label says. That matters most for the work that pulls you in: reaching behind a bus, seating a breaker, holding a probe.

Read the two fields as one statement. "8 cal/cm²" is not the answer. "8 cal/cm² at 18 inches" is.

Which equipment has to be labelled

The requirement covers electrical equipment "such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers" that is in other than dwelling units and is likely to require examination, adjustment, servicing, or maintenance while energized.

That last clause is the test, and it is about the equipment's realistic service life, not about whether anyone intends to work it energized today. Equipment that will foreseeably be examined or serviced while energized needs the label. The list of equipment types is illustrative — it opens with "such as" — so it is not a closed list to be argued down.

The two exceptions

Legacy labels. Labels applied before the effective date of the current edition remain acceptable if they complied with the labelling requirements in effect when they were applied — unless changes in the electrical distribution system have rendered the label inaccurate. An old label is not automatically a violation. An old label on a system that has since been modified is a different matter, and the exception explicitly does not protect it.

Supervised industrial installations. Where conditions of maintenance and engineering supervision ensure that only qualified persons monitor and service the system, the required information may instead be documented in a manner readily available to the people likely to perform that work. Note what this exception is not: it is not permission to skip the information. It relocates it, and "readily available" has to mean readily available at the point of work.

When the label in front of you is wrong

This is the part the label itself cannot tell you, and it is the reason to read the rest of this page.

There are two triggers to update an incident energy analysis, and most facilities operationalise only one of them.

• The calendar trigger. The analysis is reviewed for accuracy at intervals not exceeding five years, and the label data is reviewed on the same five-year clock. Where that review finds the label inaccurate, the label is updated.
• The event trigger. The analysis is updated when changes in the electrical distribution system could affect the results. The standard's informational note names what counts: changes made by the utility or another entity — transformer sizing is the example given — modifications to protective devices, and changes to protective-device settings.

The five-year clock is the one that gets managed, because it can be put in a calendar. The event trigger is the one that gets missed, because it starts somewhere else. Engineering changes a relay setting on a Tuesday. Nobody tells safety. The label on that panel is now wrong, and the PPE somebody selects from it next month is wrong with it — and the label will keep looking authoritative right up until it hurts someone, because it is printed, and printed things read as current.

There is a further input people forget: the analysis has to account for the overcurrent protective device's clearing time including its condition of maintenance. A breaker that has not been exercised or tested in twenty years may not clear in the time the study assumed. The study is only as good as that assumption, and the label is only as good as the study.

Practical version, if you are standing in front of a panel: ask what has changed since the study date. If the answer is a transformer, a breaker, a setting, or the utility service, treat the label as unverified and get it re-run.

Who owns the label

The equipment owner is responsible for the documentation, installation and maintenance of the label. Not the contractor who did the study, not the electrician who reads it, not the vendor who supplied the gear.

Two supporting requirements sit alongside that. The method of calculation and the data supporting the label information must be documented — so there should be a study behind every label, retrievable. And the label must be durable enough for the environment it lives in, which is a real requirement in wash-down, outdoor and high-vibration areas where labels fade to blank inside a few years.

A faded label is not a cosmetic problem. It is a missing label.

FAQ

Do arc flash labels expire?

Not in the sense of a printed expiry date. The data behind the label is reviewed for accuracy at intervals not exceeding five years, and the label is updated where that review finds it inaccurate. A label can also be invalidated at any time by a change in the distribution system, long before five years is up.

What does "but not both" mean on an arc flash label?

A label may carry the available incident energy with its working distance, or an arc flash PPE category taken from Table 130.7(C)(15)(a) or (b) — but not both at once. They are two different methods of selecting protection and mixing them on one label invites the wrong PPE choice.

Is a label that shows only a PPE category compliant?

Yes. The third required element permits a category, a minimum arc rating of clothing, or a site-specific level of PPE as alternatives to the incident energy figure. All are compliant. The incident energy form simply carries more information.

Does an old label have to be replaced?

Not automatically. Labels applied before the current edition took effect remain acceptable if they complied with the requirements in force when they were applied. That protection is lost if changes in the electrical distribution system have made the label inaccurate.

What if the equipment has no label at all?

Treat it as an unknown, not as a low hazard. Missing information is not evidence of low incident energy, and the absence of a label does not remove the hazard behind the door. Escalate it to the equipment owner, who carries the responsibility for the label.

Who is responsible for keeping labels current?

The owner of the electrical equipment is responsible for the documentation, installation and maintenance of the label.