Okay, let's break this down and get you the ammunition you need to stand your ground. You are absolutely right to be concerned. Hanging luminaires solely by low-voltage control wiring is a recipe for disaster and likely violates multiple code sections, even if the manufacturer is giving you the thumbs up.Here's a breakdown of why this is a bad idea and the code references you can use

Why It's Wrong (Beyond Just Code):
Safety

Low-voltage wiring is not designed to handle the weight of a luminaire. Over time, the insulation can degrade, the conductors can stretch, and the connection points can fail. This creates a serious risk of the lights falling, creating a shock hazard, and potentially causing a fire.

Liability

As the electrical contractor, you're ultimately responsible for the safe and compliant installation. Even if the engineer and manufacturer say it's okay, you're the one who will be held liable if something goes wrong.

Common Sense

Even without code, it just feels wrong. Trust your gut. You're the experienced professional here.

Code References (The Ammunition)


NEC 300.11(D) Cables Not Used as Means of Support

You've already cited this, and you're right to focus on it. The key is the phrase "non-electrical equipment." While a luminaire is an electrical piece of equipment, when you are talking about its physical support, the luminaire as a physical object is considered non-electrical equipment. You're not using the wiring as part of its electrical circuit; you're using it as a support mechanism. This is where the "non-electrical equipment" comes into play. Think of it this way: You wouldn't hang a speaker from a low voltage wire just because it needs the wire to operate, correct?

Argument

"While the luminaire itself uses electricity, its physical weight and form constitute 'non-electrical equipment' when considering the means of support. The low-voltage wiring is being used solely to support the weight of the luminaire, which violates 300.11(D)."2.

NEC 410.36 Means of Support

This section requires luminaires to be "securely supported." While it doesn't specifically say how you can't support them, it heavily implies that the support method must be adequate and robust. Supporting a luminaire by low-voltage wiring is inherently not secure.

Argument

"410.36 mandates that luminaires be 'securely supported.' Using low-voltage control wiring for support is insufficient to provide secure support and does not meet the intent of this section."3.

NEC 110.3(B) Installation and Use

This is a crucial section. It requires you to install equipment "in accordance with any instructions included in the listing or labeling." While the manufacturer might be saying it's okay, does the listing (UL, ETL, etc.) of the luminaire explicitly state that it can be supported solely by low-voltage wiring? I highly doubt it. If the listing doesn't allow it, you can't do it.

Argument

"NEC 110.3(B) requires installation according to the listing and labeling instructions. I need documentation from the manufacturer showing that their listed product is specifically designed and listed for support using only the low-voltage wiring. If there is no documentation and listing for this, it is a violation of 110.3(B)." This puts the onus on them to prove their claim.
4.

NEC 310.10(H) Support of Conductors in Vertical Raceways

While this specifically deals with vertical raceways, the principle applies. Conductors within a raceway carrying their own weight need support. It logically follows that conductors outside of a raceway should not be used to support a load.

Argument

"While this section deals specifically with conductors within a raceway, the underlying principle is that conductors themselves are not intended to be the primary structural support element. Supporting a luminaire with low-voltage wiring goes against this principle."5.

Manufacturer's Instructions (Again)

Push back HARD on the manufacturer's claim that it's okay. Get it in writing. Ask for the specific UL or ETL listing that allows this type of support. Demand documentation. If they can't provide it, they're liable.

How to Present Your Case


Be Professional and Firm

Start by explaining your concerns clearly and calmly. Emphasize that your priority is safety and code compliance.2.

Provide the Code References

Cite the specific NEC sections mentioned above, along with your interpretations of why they apply. (Copy and paste what I wrote above!)3.

Document Everything

Keep a written record of all communications with the manufacturer, engineer, and GC. If possible, get their assurances in writing.4.

Escalate if Necessary

If the engineer and GC are still resistant, escalate the issue to your supervisor or company management. Consider involving a third-party inspector or code official.5.

Don't Budge

Ultimately, you're the EC. You have the responsibility to ensure the installation is safe and compliant. Don't let anyone pressure you into doing something that you know is wrong.

Important Considerations



Local Amendments

Be sure to check for any local amendments to the NEC that might be relevant.

AHJ (Authority Having Jurisdiction)

If you're still unsure, contact your local building inspector or electrical inspector for their opinion. Their interpretation of the code is what ultimately matters.

In summary: You are right to be concerned. The engineer and GC may have overlooked some very crucial code references and safety issues. Your best argument is with NEC 110.3(B) and the manufacturer UL listing. Make them put their allowance in writing. You have plenty of valid arguments to back up your concerns. Good luck! Flag for review