NEC 110.21 - Marking: Label That Stuff (Or the Inspector Will)

The Straight Talk

Look, we've all been there. Inspector walks up to your panel, squints at it, and says, "Where's the marking?" You mumble something about it being temporary, and he gives you that look—the one that says you're about to get a red tag and he's about to get his daily entertainment.

Section 110.21 is the Code's way of saying: Everything needs a label, and that label better survive longer than your last apprentice.

Part (A)(1): Equipment Markings - The Basics

Every piece of electrical equipment needs to tell you who made it. The manufacturer's name, their logo, or some way to figure out who to curse at when it fails at 2 AM on a Saturday. Plus, all the electrical specs—voltage, current, wattage—need to be on there somewhere (other Code sections will tell you exactly what).

Here's the kicker: That label has to be tough enough to survive whatever environment it's in. If you're installing gear in a car wash, that sticker better handle getting soaked daily. If it's in a factory with caustic chemicals, it needs to laugh in the face of acid splash. "Sufficient durability" is Code-speak for "don't slap a piece of masking tape on it and call it a day."

Part (A)(2): Reconditioned Equipment - The Frankenstein Monster Rule

So somebody rebuilt that gear, huh? Maybe it fell off a truck (the inspector's assuming it did, anyway). The 2023 Code finally addressed what we've all wondered about for years: What about used/rebuilt/reconditioned/refurbished/"gently pre-owned" equipment?

Here's what needs to happen:

1. Mark it with who did the reconditioning—Company name, logo, whatever identifies who rebuilt it
2. Date stamp it—When was this Frankenstein project completed?
3. Call it what it is—Slap "RECONDITIONED" on there (or "rebuilt," "refurbished," "remanufactured"—they're playing fast and loose with the vocabulary)

The big deal: You gotta remove or deface the original listing mark (like the UL sticker). Don't just cover it—make it gone or illegible. Why? Because that original listing doesn't mean squat anymore. You messed with the equipment, it's not what UL tested, so you can't pretend it still has their blessing. The nameplate can stay (you know, the plate with model numbers and electrical ratings), just kill the listing logo.

The Exception (because there's always an exception): If you're in an industrial facility where only qualified people touch the gear, and the owner is reconditioning their own equipment as part of regular maintenance, you can skip the reconditioning label. It's the "we know what we're doing, trust us" clause. Your residential service calls don't qualify, sparky.

Part (B): Field-Applied Hazard Markings - Warning Labels That Actually Warn

Sometimes YOU have to add the warning labels in the field. Arc flash labels, GFCI warning signs, that "DO NOT OPEN - LIVE PARTS" sticker you should've put on before the helper opened it anyway.

Two rules here:

Rule 1: The label has to survive its environment AND actually communicate the hazard. Words, colors, symbols—whatever works. If you install it outdoors and it fades to nothing in six months, that's not "sufficient durability." If you write it in ancient Sumerian, that's not "effective words."

Rule 2: No handwriting. Period. Well, almost period—there's an exception.

You need to permanently affix these warnings. Not tape. Not a sticky note. Not a Sharpie on the door (though we've all seen it). Get a label maker, use an engraver, get proper pre-printed labels—whatever. Just make it permanent and legible.

The Exception: If part of the marking changes (like fill-in-the-blank info for specific fault current or available short-circuit current), THAT part can be handwritten. But it still has to be legible. Your chicken-scratch doesn't count.

Key Takeaways (The Stuff That Actually Matters)

1. All equipment must be marked with manufacturer ID and electrical ratings
2. Markings must survive the environment they're installed in (no wimpy labels)
3. Reconditioned equipment needs three things: Who reconditioned it, when, and the word "reconditioned" (or equivalent)
4. Original listing marks must be removed from reconditioned equipment—you can't ride on the original approval
5. Exception for industrial owners doing their own maintenance reconditioning with qualified personnel only
6. Field-applied hazard warnings must be permanent—no handwriting (except variable data)
7. Permanent means permanent—affixed to the equipment/method, not taped on
8. Labels must actually communicate the hazard effectively (duh, but the Code has to say it)

Real-World Scenarios (Why This Rule Exists)

Scenario 1: The Mystery Panel

You're troubleshooting a dead circuit in a commercial building. You pop open a sub-panel and... nothing. No manufacturer name, no ratings, no listing mark. Is it 120/240V or 277/480V? Is it rated for 100A or 200A? Who made this thing—Fisher-Price?

You're now playing electrical roulette because somebody installed unmarked junk or the label fell off years ago. This is why durable markings matter. You shouldn't need a detective and a prayer to work safely.

Scenario 2: The "Reconditioned" Switchgear

Customer saved $30K buying "reconditioned" switchgear online. Looks great, works great, has a shiny UL label on it. Inspector shows up and red-tags it immediately. Why? Because someone rebuilt that gear, but left the original UL listing on it. UL didn't test THIS version—they tested the original configuration. That listing is now a lie.

The proper move: Remove the UL label, add a "RECONDITIONED BY [Company Name], [Date]" plate, and get the inspector to approve it based on what it IS, not what it WAS. (And good luck with that—inspectors love reconditioned gear about as much as they love unmarked panels.)

Scenario 3: The Sharpie Warning Label

You installed a service with a 22kA available fault current. You grabbed a Sharpie and wrote on the panel cover: "WARNING 22kA AFC." Proud of yourself for doing the right thing and warning people.

Inspector fails it. Why? Because Sharpie isn't permanent in the Code's eyes—it'll fade, smudge, or get wiped off. Get a proper engraved label or at minimum a quality printed adhesive label rated for the environment. Your handwriting isn't allowed here (unless it's filling in pre-printed blanks on an approved label).

Scenario 4: The Industrial Maintenance Exception

You work maintenance at a huge chemical plant. You've got a 20-year-old motor starter that's been rebuilt in-house three times—new contacts, new coils, checked and tested by your engineers who literally teach arc flash courses. Do you need to deface the original listing and label it "reconditioned" every time?

Nope! The exception covers you. Your facility has qualified personnel, you're the owner doing your own maintenance, and it's part of a regular program. Document it in your maintenance records, but you're not required to relabel it as reconditioned. (Don't try this at home—or in commercial/residential work.)

What to Study (For License Exams)

Test writers LOVE this section because it's new content (the reconditioned equipment stuff especially) and it's straightforward to quiz. Here's what to drill:

1. Know the three requirements for reconditioned equipment markings: Who reconditioned it, when, and "reconditioned" label
2. Original listing marks must be removed—this is a gimme test question
3. Know the industrial exception for owner-maintained equipment with qualified personnel
4. Field-applied hazard markings can't be handwritten (memorize the exception for variable/changeable data)
5. "Sufficient durability" means survives the environment—match the label to the conditions
6. Markings must be permanently affixed—not tape, not temporary
7. Know that reconditioned approval is NOT based solely on original listing

Test Question Alert: Expect scenarios like: "A contractor reconditions a panelboard. What markings are required?" or "Can you handwrite an arc flash warning label?" The answers are in this article—know them cold.

Pro Tip: If you see "reconditioned," "rebuilt," "refurbished," or "remanufactured" on a test question, they're all treated the same per Informational Note No. 2. Don't overthink it.

The Bottom Line

Label your stuff. Label it right. Label it so it lasts. If you recondition something, admit it and label it properly—don't try to pass it off as factory-fresh. And for the love of all that's holy, stop using Sharpies for permanent warning labels.

The inspector will check. The lawyer will ask after the accident. Future you (or the poor soul troubleshooting at midnight) will thank you.

Remember: If it's not marked, it's not right. If it's marked in Sharpie, it's still not right. Get a label maker, keep it in your van, and use it.

Now get back to work.