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Thread: PV conductor transition from PV cable to THWN-2

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    PV conductor transition from PV cable to THWN-2

    I am reviewing this project and have a question about the cables transitioning from PV cable to THWN-2.

    they show "quantity 3" PV cables to transition JB but "quantity 1" THWN-2 cables from JB to inverter.

    Shouldn't it also be "quantity 3" THWN-2 cables from JB to inverter?

    Please see pic for better info and let me know how you interpret it..

    pic: https://ibb.co/tMYJMt9

    Thank You

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    I have found that the solar engineering leaves a lot to be desired.
    I guess anyone can become a solar engineer.
    Tim
    Master Electrician
    New England
    Yesterday's Technology at Tomorrow's Prices

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    Quote Originally Posted by tkb View Post
    I have found that the solar engineering leaves a lot to be desired.
    I guess anyone can become a solar engineer.
    I don't know what you mean by the first comment, but I agree with the second one. Anyone can become an engineer; all you have to do is go to school and earn an engineering degree.

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    Seems to me they should both say 6.

    PV design is super competitive in many areas now, people are churning them out and don't necessarily make the time to proofread.

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    DC

    Quote Originally Posted by Designer69 View Post
    I am reviewing this project and have a question about the cables transitioning from PV cable to THWN-2.
    they show "quantity 3" PV cables to transition JB but "quantity 1" THWN-2 cables from JB to inverter.
    Shouldn't it also be "quantity 3" THWN-2 cables from JB to inverter?
    Please see pic for better info and let me know how you interpret it..
    Thank You
    I assume this is a DC combiner? It is not unusal to have several strings using PV Wire in air come to a DC combiner and leave as a single circuit using THWN in EMT or PVC.

    You cannot just parallel strings of modules without overcurrent protection so 3:1 is not just a simple splice.

    For those who responded without addressing the question, thanks for nothing!
    e^(i pi) = -1

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    Quote Originally Posted by beanland View Post
    I assume this is a DC combiner? It is not unusal to have several strings using PV Wire in air come to a DC combiner and leave as a single circuit using THWN in EMT or PVC.

    You cannot just parallel strings of modules without overcurrent protection so 3:1 is not just a simple splice.

    For those who responded without addressing the question, thanks for nothing!
    They are showing a Solaredge inverter with 3 strings landed on a common bus. No combiner. Solaredge is fine with this but provides an alternative version with fuses in case the AHJ insists on it.

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    Quote Originally Posted by beanland View Post
    You cannot just parallel strings of modules without overcurrent protection so 3:1 is not just a simple splice.
    Each string must have it's own individual ocpd? So the combiner box has a fuse for each string? Is this this a code requirement somewhere?


    I understand there is only one DC ocpd at the solaredge inverter.

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    Quote Originally Posted by jaggedben View Post
    They are showing a Solaredge inverter with 3 strings landed on a common bus. No combiner. Solaredge is fine with this but provides an alternative version with fuses in case the AHJ insists on it.

    the riser seems to show the 3 strings landed on a common bus right at the inverter (which would indicate to me actually 6 thwn-2 cables from JB to inverter)

    however, the schedule says "1" for thwn-2 cables from the JB to the inverter which makes me think it is actually a combiner box and the common bus tie-in point.

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    Quote Originally Posted by Designer69 View Post
    the riser seems to show the 3 strings landed on a common bus right at the inverter (which would indicate to me actually 6 thwn-2 cables from JB to inverter)

    however, the schedule says "1" for thwn-2 cables from the JB to the inverter which makes me think it is actually a combiner box and the common bus tie-in point.
    First of all the plan you posted shows single conductors in raceways, which is not 'cables'. Hence they should show '6' conductors for 3 strings (3 positive, 3 negative), as this is what is relevant for any derating calculations if a ground is not included. Or '7' for fill, if ground is included.

    As far as your logic about combining, that's a reasonable supposition except that it's contradicted by the following:
    -The line schematic doesn't show combining in the j-box, it shows it in the inverter.
    -No fuses are shown
    -One who is familiar with installing the actual inverter (SE10000H) will know that the 'combining' is typically done in the inverter via the terminal block provided, which does not have fuses. This also matches the drawing.

    So I would go back to whomever made the plan and request clarification. The table does not match the drawing, simply put.

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    Quote Originally Posted by Designer69 View Post
    Each string must have it's own individual ocpd? So the combiner box has a fuse for each string? Is this this a code requirement somewhere?


    I understand there is only one DC ocpd at the solaredge inverter.
    With traditional PV strings (modules in series) fuses were required by 690.9 when you had more than two strings (essentially, though not precisely). With optimizers the same logic does not exactly apply and code interpretation is a bit of a grey area. SolarEdge has white paper explaining why fuses are not necessarily required but the code isn't clear cut enough that all AHJs will necessarily accept it.

    http://www.solaredge.com/files/pdfs/...quirements.pdf

    Note: The drawing you posted shows no fuses.

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