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I've been trying to understand the NFPA70/NEC a bit better the last few weeks. If a part or component is UL-listed (or listed by another NRTL), is this the sole criterion for whether that part or component is permitted to be installed in a junction box?

For instance, I stumbled across several industrial servo motors that are UL listed. Supposing that there is a particular model which would fit in a junction box, would this:

  1. Technically pass inspection?
  2. Be likely to pass inspection in the practical sense in most jurisdictions?

Over the years I must have seen many pieces of electronics and home appliances that have had the UL mark, none of which seem appropriate for direct wiring. So, I suppose I already know the answer to my own question... what I want is confirmation.

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    AIUI, part of the "Listing" includes following the manufacturer's instructions on installing the device. If you're looking to install a motor in a junction box, but the instructions don't say you can do that, then no, that technically wouldn't pass an inspection. Most inspectors would probably flag it, as seeing a motor in a junction box would, most likely, grab their attention pretty quickly.
    – FreeMan
    Mar 16, 2022 at 19:52

2 Answers 2

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FreeMan nailed it.

You must follow the entire electrical code.

You're focusing on 110.2 but actually, you must follow the entire electrical code. If you read the rest of it, eventually you will reach 110.3, which settles the question.

Equipment must be installed according to its labeling and instructions.

If the labeling and instructions for that servo-motor instructs you how to install it in a junction box and use it for whichever home-automation task you are attempting, then show that to your inspector, who will go "I'll be darned".

But generally, components like servo-motors simply do not have any instructions for such a use.

Why is this important? Because UL approves the labeling and instructions as part of the equipment listing. Listings are based on testing, and testing is limited in scope. The scope is defined by the instructions and labeling - they don't test for off-label use.

Keep in mind that electrical components don't get "UL Listed" marks, they get "UR Recognized" (marked as ЯU). And they should have a file number. UL isn't faked as often as CE, but it is still faked. Chain of custody is your friend; Amazon is your enemy. Mouser and Home Depot know their sources. Amazon is rife with "Amazon Marketplace" (read: eBay) items, and even for their own items, thanks to "commingling" they've lost control of their chain of custody. Very foolish on their part.

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  • The weird thing is... what if the instructions are generic enough to encompass mounting in a junction box? I was thinking it would be more of a slam dunk "definitely not allowed"... where this seems like if I shopped around for just the right servo this is still (barely) in "maybe" territory. Thank you for your answer.
    – John O
    Mar 17, 2022 at 1:42
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    Then the "maybe" comes down to the interpretation of the inspector looking at your work, @JohnO, and her opinion may be different than yours. Lots of room for you to lose the battle and have to redo it. May as well save yourself the trouble and do it "right" the first time.
    – FreeMan
    Mar 17, 2022 at 12:21
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    Thanks for the hat-tip, Harper! If I'd known the actual code reference, I'd have answered, but, alas, I'm only an internet ranger. :(
    – FreeMan
    Mar 17, 2022 at 12:22
  • @FreeMan Thanks for the advice and clarification. I will keep all of it in mind, and at the moment most of this is just theoretical anyway. The biggest impediment of course is finding a UL-listed servo that's even small enough for my purpose, those tend toward the larger sizes rather than the hobbyist-sized ones I'm more familiar with. Then to study the instructions for them and see if there's any wiggle room. If they talk generically about mounting them to a solid surface and allow them to be wired with wiring nuts... I might make my decision then.
    – John O
    Mar 17, 2022 at 14:06
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I think the key is what does "UL Listed" actually mean? I found a useful description.

From that site,

A basic concept is that "Listing" can only refer to stand-alone products with a specific function, tested against UL's published and nationally-recognized standards for safety for a specific category of equipment.

For example,

Power supplies achieve UL recognition by evaluation against particular applicable standards, for example, the familiar UL 60950 for IT equipment (soon to be superseded by UL 62368), or UL 60601-1 for medical applications.

This section seems to answer your question:

While there will be testing agencies around the world that use the term UL approved, the US test and certification agency certainly does not. In fact, if you look at their website, the only mention of "approvals" is in examples of incorrect terms. UL avoids the word as a way of indicating that it really is the manufacturer's responsibility to ensure safety and that UL only acts as an auditor to check samples and documentation while making factory visits to confirm that procedures are being followed. The term "certification" is used for some UL marks, but only to communicate that UL has successfully tested a sample product against certain specifications. The term's usage is not meant to imply that it "approves" of the use of the product or component in all potential applications.

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