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CBO
If there’s one NEC article that gets overlooked far too often, it’s 110.3(B). It is a single sentence with massive implications, and the 2023 edition of the NEC makes it even more explicit. It now states that equipment that is listed, labeled, or identified for a use shall be installed and used in accordance with any instructions included in the listing, labeling, or identification. An informational note was added to clarify that these instructions may be printed, delivered by QR code, or hosted online. Whether a sticker is slapped on the product or the manual is buried in a PDF, the bottom line is this: if the manufacturer says it must be installed a certain way as part of the listing, then that becomes enforceable code.
This is not new. The 2020 NEC already required listed or labeled equipment to be installed according to its instructions. The 2023 version expands the scope to include equipment “identified for a use,” which matters when dealing with custom or application-specific equipment. The code panel also clarified how installation instructions are delivered, which reflects how the industry actually works today. Digital documentation is common but does not reduce the legal obligation to follow it.
What gets missed is how this ties into something like voltage drop. While the NEC has an informational note in 210.19 suggesting a maximum of 5 percent combined voltage drop, that is not a code requirement.
However, when a manufacturer sets a minimum voltage or states a maximum allowable voltage drop in its listing, 110.3(B) makes it mandatory. It does not matter if the rest of the code treats voltage drop as a recommendation. If the listed equipment requires a minimum voltage at its terminals, you enforce it. That is the law. And that means the installer has to do the math before they pull the wire, not after the inspector calls them out on it.
This plays out in real-world scenarios all the time. Think about long feeder runs to manufacturing equipment or remote installations where the voltage at the load could easily fall below spec. If the equipment documentation says “minimum operating voltage: 208 volts,” and the engineer’s calculation puts it at 204 volts under full load, that is a problem. As the AHJ, you can and should require proof that the installation complies with the listing. That is what 110.3(B) demands. The same principle applies to transformers, EV chargers, HVAC equipment, or anything else where the operating voltage is part of the listing criteria.
Manufacturers put those instructions there for a reason. They are part of the safety testing and evaluation process. Whether the equipment is listed by UL, ETL, or another NRTL, the performance parameters are not suggestions. If the label says “do not install above a receptacle,” then that’s code. If it says the product must maintain a minimum spacing from combustible material, that’s code. And if it says the voltage must be within a specific range, that’s code too.
Too many installers treat listing instructions like optional reading material, and too many inspectors fail to enforce them. That has to change. The industry needs to stop thinking of listing labels as fine print and start recognizing them as code language. If a product is listed and part of that listing includes installation criteria, then 110.3(B) gives you the authority and the responsibility to hold people to it.
Some people like to argue about what the NEC does or does not explicitly require. But 110.3(B) closes that door. It is one of the most powerful tools an AHJ has, and yet it is often misunderstood or ignored. It is time to stop overlooking it.
This is not new. The 2020 NEC already required listed or labeled equipment to be installed according to its instructions. The 2023 version expands the scope to include equipment “identified for a use,” which matters when dealing with custom or application-specific equipment. The code panel also clarified how installation instructions are delivered, which reflects how the industry actually works today. Digital documentation is common but does not reduce the legal obligation to follow it.
What gets missed is how this ties into something like voltage drop. While the NEC has an informational note in 210.19 suggesting a maximum of 5 percent combined voltage drop, that is not a code requirement.
However, when a manufacturer sets a minimum voltage or states a maximum allowable voltage drop in its listing, 110.3(B) makes it mandatory. It does not matter if the rest of the code treats voltage drop as a recommendation. If the listed equipment requires a minimum voltage at its terminals, you enforce it. That is the law. And that means the installer has to do the math before they pull the wire, not after the inspector calls them out on it.
This plays out in real-world scenarios all the time. Think about long feeder runs to manufacturing equipment or remote installations where the voltage at the load could easily fall below spec. If the equipment documentation says “minimum operating voltage: 208 volts,” and the engineer’s calculation puts it at 204 volts under full load, that is a problem. As the AHJ, you can and should require proof that the installation complies with the listing. That is what 110.3(B) demands. The same principle applies to transformers, EV chargers, HVAC equipment, or anything else where the operating voltage is part of the listing criteria.
Manufacturers put those instructions there for a reason. They are part of the safety testing and evaluation process. Whether the equipment is listed by UL, ETL, or another NRTL, the performance parameters are not suggestions. If the label says “do not install above a receptacle,” then that’s code. If it says the product must maintain a minimum spacing from combustible material, that’s code. And if it says the voltage must be within a specific range, that’s code too.
Too many installers treat listing instructions like optional reading material, and too many inspectors fail to enforce them. That has to change. The industry needs to stop thinking of listing labels as fine print and start recognizing them as code language. If a product is listed and part of that listing includes installation criteria, then 110.3(B) gives you the authority and the responsibility to hold people to it.
Some people like to argue about what the NEC does or does not explicitly require. But 110.3(B) closes that door. It is one of the most powerful tools an AHJ has, and yet it is often misunderstood or ignored. It is time to stop overlooking it.
