90.7 - Examination of Equipment for Safety

Or: "Why We Trust the UL Sticker (And Why Inspectors Do Too)"

The Plain-English Translation

Alright, listen up. You know those little hologram stickers on electrical equipment that say UL, ETL, CSA, or whatever? This section is basically the NEC saying, "Look, we're not gonna reinvent the wheel here."

Here's the deal: When legit testing labs (like UL, Intertek, CSA, etc.) put their stamp on equipment, they've already beaten the crap out of it in ways you can't imagine. They've melted it, frozen it, overloaded it, and probably made it listen to Nickelback on repeat. If it survives and gets listed, the NEC says, "Good enough for us!"

Translation of that second paragraph: When you're installing factory-built equipment that's properly listed, the inspector doesn't need to crack it open and check every wire inside like some kind of electrical surgeon. That internal wiring was already approved at the factory. The inspector's job is just to make sure:

• You didn't Frankenstein it with modifications
• It didn't get dinged up by the forklift driver (again)
• You're installing it according to the instructions (yeah, those things we all throw away)

Think of it like this: When you buy a new truck, the DMV doesn't make you pop the hood to verify Ford wired the engine harness correctly. They just check that you didn't bolt a snowplow to the roof with drywall screws. Same principle.

Key Takeaways (The Stuff That Actually Matters)

Technical Requirements:

1. Listed equipment gets a pass on internal inspection - If it's got that UL (or equivalent) listing, the guts are pre-approved
2. "Qualified electrical testing laboratory" - Not your buddy Gary who "knows stuff." We're talking NRTL (Nationally Recognized Testing Laboratory) certified organizations
3. Factory-installed internal wiring = hands off - Don't need to inspect what the manufacturer did, only what YOU do
4. Two exceptions to the free pass:
   • Evidence of alterations (somebody got creative with a drill)
   • Physical damage (it fell off the truck, didn't it?)
5. Reference to 110.3(C) - This is the money shot that requires you to install listed equipment per the instructions (yes, seriously, read them)

Critical Point: "Listed" has a specific definition in Article 100 - it's not just "I found it on a list somewhere." It means tested, approved, and tracked by a qualified lab.

Real-World Scenarios (Tales from the Trenches)

Scenario 1: The Curious Inspector

You're installing a shiny new 400A panel with factory-installed guts. The inspector shows up and starts talking about "needing to verify the internal busing and terminations."

Wrong approach: Let him waste two hours dismantling a perfectly good panel.

Right approach: "Hey, this panel's UL listed under file number [check the label]. Section 90.7 says you don't need to inspect factory-installed internals unless there's damage or alterations. Wanna check the label together?"

Why it matters: Saves everybody time, and you look like the pro who knows the code.

Scenario 2: The Frankenpanel

Your predecessor decided the 200A panel could "totally handle" an extra 100A breaker if they just drilled some new holes in the back and added their own busing. Real creative type.

The problem: That panel's listing just went out the window faster than a apprentice on Friday at 2 PM. It's been altered, so 90.7 protection doesn't apply anymore.

The fix: Rip it out. Start over. Bill the hack who created this mess (good luck collecting).

Why it matters: The moment you modify listed equipment, you've voided the testing lab's approval. Now YOU own any problems, and your liability insurance just got nervous.

Scenario 3: The Forklift Incident

A gorgeous, UL-listed transformer gets delivered to the job. Then the forklift operator—who swears he's "driven these things for years"—puts a fork straight through the enclosure.

What 90.7 says: Internal inspection is now REQUIRED because there's visible damage. That UL sticker doesn't mean squat if the guts are scrambled.

Why it matters: You can't just slap some duct tape on it and say "she's listed!" Damage = inspection. Period.

Scenario 4: The "Just as Good" Equipment

Contractor brings in panels from "Dave's Discount Electrical Warehouse & Bait Shop." No UL listing, no ETL, no nothing. Just says "Tested by Dave" with a Sharpie.

The inspector says: "Nope."

Why? Section 90.7 specifically requires testing by organizations "properly equipped and qualified for experimental testing." Dave's garage doesn't count, even if he has a really nice multimeter.

Why it matters: Using non-listed equipment is like showing up to a code inspection with a permission slip you wrote yourself. Not happening.

What to Study (Exam Prep Reality Check)

High-probability exam topics:

1. What "listed" actually means - They LOVE asking this. Know that it requires a qualified testing lab (NRTL), not just any testing.

2. When internal inspection IS required - Damage or alterations. Expect a scenario question where equipment is modified and you need to know the listing is now void.

3. The 110.3(C) connection - This is testable gold. Listed equipment must be installed per the listing and manufacturer instructions. They'll give you a scenario where someone ignores instructions and ask if it's compliant.

4. Factory-installed vs. field-installed - Know the difference. Factory = pre-approved. Field = that's on you, buddy.

5. Definition of qualified testing laboratory - Expect questions about whether random testing outfits count. Answer: Only NRTL-recognized labs.

Exam question example you might see:

"An electrician installs a UL-listed panelboard but modifies the internal busing to accommodate additional circuits. According to 90.7, is the listing still valid?"

Answer: Nope. Alterations void the listing. The equipment now requires inspection as if it were never listed.

Study tip: Cross-reference this with Article 100's definition of "listed" and "labeled," plus 110.3(C) about installation per listing instructions. These three sections form the holy trinity of "equipment approval" questions.

The Bottom Line

Section 90.7 is the NEC's way of saying, "We trust the professionals at testing labs, so we don't need to make electricians and inspectors reinvent the wheel." But that trust comes with conditions: don't modify it, don't damage it, and for the love of Mike, install it according to the instructions.

That little UL sticker is worth its weight in gold—it's your get-out-of-internal-inspection-free card. Respect it, protect it, and don't screw with the equipment it's attached to.

Now get back to work, and remember: if it ain't listed, it ain't legit. Unless you want to be the one explaining to the inspector why Dave's Bait Shop should be considered a "qualified testing laboratory." (Spoiler: that's not a fight you'll win.)