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Thread: UL Listed Terminal Blocks

  1. #1
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    UL Listed Terminal Blocks

    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?

  2. #2
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    I don't know that any are available that are actually listed.
    Bob

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    Quote Originally Posted by petersonra View Post
    I don't know that any are available that are actually listed.
    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.
    Bob

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    petersonra, can you provide a code reference?

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    Quote Originally Posted by PWDickerson View Post
    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.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2017 NEC unless otherwise noted.

  6. #6
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    Quote Originally Posted by rbalex View Post
    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.

  7. #7
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    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.
    Just because you can, doesn't mean you should.

  8. #8
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    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...
    Moderator-Washington State
    Ancora Imparo

  9. #9
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    Back to my original question. How are others transitioning from PV wire to THWN-2?

  10. #10
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    Wire nuts.

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