Listing

[bwat]

Background details:
- Designing MW-scale PV site
- Major manufacturer (mfr) has UL listed skid that is comprised of several components
- The same major mfr can swap out one of the components within the skid to meet our specific requirements. The skid would no longer be listed then.
- The new part that they're putting into it is listed


Anybody know how this would all work from code and listing requirements and what I need to watch out for?

It seems like this is then just the same as if it were site-built, so I'm wondering what the biggest risks and concerns would be.

 

[Dennis Alwon]

Is the skid UL Listed or UL Recognized. I believe if it is UL recognized then the parts can be ul listed and you are good. I am sure Don will set me and you straight but there is a difference. Sorry that I am not totally clear on this issue

 

[bwat]

Is the skid UL Listed or UL Recognized. I believe if it is UL recognized then the parts can be ul listed and you are good. I am sure Don will set me and you straight but there is a difference. Sorry that I am not totally clear on this issue

The skid would otherwise be UL Listed. But I'm not sure how listed vs recognized makes a difference here since they're losing whichever one it was with the custom equipment swap?

 

[pv_n00b]

NEC 90.7 is our friend. It says in part:

It is the intent of this Code that factory-installed internal
wiring or the construction of equipment need not be inspected
at the time of installation of the equipment, except to detect
alterations or damage, if the equipment has been listed by a
qualified electrical testing laboratory that is recognized as
having the facilities described in the preceding paragraph and
that requires suitability for installation in accordance with this
Code. Suitability shall be determined by application of requirements
that are compatible with this Code.

The internal components of listed equipment are not subject to inspection by the AHJ to determine if they comply with the NEC. Often they do not comply but they have been tested and found to be safe if the equipment is installed in compliance with the listing. If the skid is UL listed then the AHJ can't poke around and say a conductor is undersized, an OCPD is not properly rated, etc. Strip away the UL listing and now the AHJ is free to call out all the NEC violations they can find inside.
So the results depend on your AHJ and how much of an explorer they want to be. I remember an AHJ who looked inside an inverter and pointed at an internal wire and said it is not sized to the NEC requirements. They were pointed toward NEC 90.7 and that was the last anyone heard of the issue.

 

[pv_n00b]

Is the skid UL Listed or UL Recognized. I believe if it is UL recognized then the parts can be ul listed and you are good. I am sure Don will set me and you straight but there is a difference. Sorry that I am not totally clear on this issue

Using UL Recognized components simply allows a manufacturer to build a UL Listed device more easily at less cost. If they build their device with a UL Recognized component then it reduced the amount of testing UL needs to do to list the device since the UL Recognized component has already been tested. UL Recognized components have undergone limited testing for the purpose of being included in a larger UL Listed device and are not listed to be used alone.

 

[don_resqcapt19]

Depending on what the change involves as far as potential safety issues, the AHJ may require a field evaluation. The following is from the 2020 code.

691.5 Equipment.
All electrical equipment shall be approved for installation by one of the following:

• (1) Listing and labeling
• (2) Be evaluated for the application and have a field label applied
• (3) Where products complying with 691.5(1) or (2) are not available, by engineering review validating that the electrical equipment is evaluated and tested to relevant standards or industry practice

If the manufacture is making this change, they should be able to maintain the listing, unless this change results in equipment that does not comply with all of the requirements of the listing standard. If that is the case, and if I were the AHJ, I would most likely require a field evaluation of the product.

 

[bwat]

Thank you @pv_n00b and @don_resqcapt19. Very helpful.