UL Listing of Resistor Box 1

[living2learn]

I have a situation where resistors must engage to correct a problem. The Vendor has bought some off the shelf NON UL Listed resisotrs and threw them in a hoffman box UL Listed.

My understanding was everything must be UL Listed.

This is a project in USA. I am asking the AHJ, but in the meantime I would like some opinions.

Side question. Can you add UL components to make a control panel and have the panel be UL Listed? Vendor says you can. My thought was the assembly must be certified, not just the components, but the components combined.

 

[jraef]

If it can be classified as an "Industrial Control Panel", then is must have a listing from an NRTL, Nationally Recognized Testing Lab, of which UL is the most well known. There are several others, outlined in a website maintained by OSHA.

The definition of an ICP is in article 409 of the National Electric Code.
Industrial Control Panel. An assembly of two or more
components consisting of one of the following:
(1) Power circuit components only, such as motor controllers,
overload relays, fused disconnect switches, and
circuit breakers
(2) Control circuit components only, such as pushbuttons,
pilot lights, selector switches, timers, switches, control
relays
(3) A combination of power and control circuit components
These components, with associated wiring and terminals,
are mounted on or contained within an enclosure or mounted
on a subpanel. The industrial control panel does not include
the controlled equipment.

The point being, if the ONLY thing in the box is the resistors, then it does not need to be listed separately.
By the way in the component count, the box and back panel do not count.



"Will work for (the memory of) salami"

 

[living2learn]

Thanks so much for the great response!

That makes sense, but the resistors are not listed by a NRTL?

 

[jraef]

Not likely. Resistors would be a COMPONENT, so at best would likely be able to be a "Recognized Component", which for UL would bear the backward UR symbol. That means it can be used as a component IN a UL listed assembly, but not stand-alone. But like I said, if these are just stand-alone, technically there is no requirement that they be NRTL listed as far as I know. Article 90.7 of the NEC requires examination for safety, and it mentions that IF something is factory assembled and listed by an NRTL, it alleviates the local inspector of the task, because he will just look for that label. So in not using a listed assembly, the risk is that the local AHJ may not like what he sees and (if you didn't already understand this) they are the Gods of their own little worlds so what they say goes. Technically you can appeal, but I have NEVER seen that go well, even if someone wins. They are, after all, human and subject to vengeful feelings...

"Will work for (the memory of) salami"

 

[btrueblood]

You might be able to get a UL 508A listed panel shop to make the panel for you, it would carry a UL listing under their certification as a UL shop...but, they would have to find UL-recognized resistors to build it with.