UL Listed Terminal Blocks

PWDickerson

Senior Member
The vast majority of our jobs are residential 1 to 4 string installations. We typically install a junction box on the roof under a module, run the PV wire to the junction box, transition to THWN-2 using a terminal block, and run the THWN-2 from the j-box down to the inverter. We have been using the same high quality terminal block for years, and it works great. The terminal block is "UL Recognized" and CSA certified (no US or C/US), but not "UL Listed". We recently got a correction from an electrical inspector because the terminal blocks are only UL Recognized instead of UL Listed. I started looking into other products we could use instead, and it looks like most, if not all, terminal blocks are only UL Recognized.

How are others transitioning from PV wire to THWN-2?
 

rbalex

Moderator
Staff member
petersonra, can you provide a code reference?
He can’t, because it’s just the opposite of what should be happening. Your inspector should be citing a specific Code or local amendment that listing is required. An inspector cannot require it just because he thinks it’s a good idea.
 

ggunn

PE (Electrical), NABCEP certified
He can’t, because it’s just the opposite of what should be happening. Your inspector should be citing a specific Code or local amendment that listing is required. An inspector cannot require it just because he thinks it’s a good idea.
Unfortunately, in some cases he can do just that. I know of a PV inspector in a major metro area who has no one with a technical background outranking him and no peer review or appeal for any decisions he makes, and he makes some bad ones.
 

jim dungar

Moderator
Staff member
A terminal block, that mounts to a rail, is not a stand-alone device and therefore cannot be UL Listed. Because it is a component, it is UL Recognized only.

This is the same thing as a plug-in relay which must be used with a socket of some type. Check the UL White book for more information.
 

tom baker

First Chief Moderator
Staff member
A recognized component can only be used by a panel mfg or UL shop. Our AHJs don't allow recognized components by themselves.
There are terminal strips available that are UL listed. but they are not as nice as a the DIN rail terminal blocks...
 

jim dungar

Moderator
Staff member
A recognized component can only be used by a panel mfg or UL shop.
I don't believe that is absolutely true. Field installation is allowed.

According to the White Book: " Many UL investigations of equipment involve an evaluation of the suitability of components such as relays, thermostats, switches, etc. for specific applications. Where such components are designed to comply with all the construction and performance requirements of the category, they are eligible for UL Listing and suitable for either field or factory installation."
However it also goes on to say:
"The Recognized Component Mark does not provide evidence of listing or labeling, which maybe required by installation codes or standards"
 

shortcircuit2

Senior Member
Power Distribution Blocks (PDB) used in junction boxes are required to be listed according to 314.28(E)(1) and when used in a wireway 376.56(B)(1)

Field installed PDB's require covers over live parts.

UL recognized parts are not for field installation, except for a direct replacement.
 

pv_n00b

Senior Member
A little background, most people have heard about the UL Recognized Component Mark but few have actually read what UL says it is for.
UL RECOGNIZED COMPONENT MARK​
UL Component Recognition means that UL has evaluated components or materials intended for use in a complete product or system. These components are intended only for end-use products that may be eligible for UL certification.​

The UL Recognized Component is a shortcut for manufacturers. If you are a manufacturer building some type of equipment you can make it easier and cheaper to list if you use UL Recognized Components in the equipment because they are already tested and do not need to be retested.

Anyone can use components with a UL Recognized Component Mark, no law against it. But putting together a bunch of UL Recognized components does not create a UL Recognized Component or a UL Listed device unless the assembly is done under the direction of a manufacturer who has got a UL Listing for a device that is assembled out of UL Recognized components in the field. If someone uses a component to make up something in the field like a transition box the UL Recognized Component Mark just becomes meaningless.

One thing to keep in mind is that the NEC does not specifically require that every electrical device is UL Listed but NEC 110.2 does require that all, "conductors and equipment required or permitted by this Code shall be acceptable only if approved," and many AHJs rather than take on the responsibility of approving equipment themselves, as defined in 110.3, will require the use of a UL Listed device if it is available. If there is a UL Listed device for performing transitions an AHJ can require that it be used based on the NEC.
 

PWDickerson

Senior Member
I am still hoping to hear how others are transitioning from PV wire to THWN-2 at the roof in residential systems. I have "wire nuts" from JaggedBen. Anyone else?
 

csoc64

Senior Member
I am still hoping to hear how others are transitioning from PV wire to THWN-2 at the roof in residential systems. I have "wire nuts" from JaggedBen. Anyone else?
Local AHJ's in my area do not allow wire nuts, so we use insulated connectors like Burndy BIBD type.
 

don_resqcapt19

Moderator
Staff member
The code does not require terminal blocks be listed.

An inspector cannot require they be listed UNLESS the AHJ had made a local amendment to that effect.
The AHJ has to approve all equipment used in an installation. Often they base their approval on a listing if there is a listed product available.
 

PWDickerson

Senior Member
We usually use Burndy clear tap's when we do a line-side connect or feeder tap. They make a very solid splice, but when used for the DC splice, they take up a lot of room in a j-box, and they are expensive. I was hoping to find some ideas for an equally solid, more compact, and less expensive solution.
 
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