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Thread: high voltage battery combiner

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    high voltage battery combiner

    So I'm installing a system with two high voltage LG batteries and it appears I need to use a fused combiner to parallel them. Max voltage for each battery unit is 570V. 'Peak current' is 18.9A but no short circuit current rating is listed. The circuit is ungrounded. A battery combiner is a first for me, and I have some questions:

    Under the 2014 NEC...

    - For two batteries, would a battery combiner be required by the Code if not required by the manufacturer, if all wiring were sized to handle current from both batteries?
    - Under the 2014 NEC, would you say both positive and negative need to be fused, or just one side (i.e. positive)?
    - Does the code require such a combiner to be listed?

    Opinions wanted. There doesn't seem to be much code guidance on this in the 2014, or even the 2017.

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    Some day when I grow up, I would like to at least understand one PV thread.

    It really is a different world then general electrical.

    I thought I had a shot at the EGC/GEC thread a few days ago, but gave up....sigh.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    uh.. thanks for the response.

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    Quote Originally Posted by jaggedben View Post
    uh.. thanks for the response.
    I am utterly clueless about PV except that I am pretty sure it possibly involves sunlight.

    I got voltage, fuse, and parallel from the first sentence. Everything in between and after is Greek to this dumb bunny.

    It is definitely specialized. I wish I had time to learn it, sounds pretty cool.
    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by jumper View Post
    Some day when I grow up, I would like to at least understand one PV thread.

    It really is a different world then general electrical.

    I thought I had a shot at the EGC/GEC thread a few days ago, but gave up....sigh.
    I always say that if you do PV you have to stand on your head when you read the electrical code.

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    Quote Originally Posted by ggunn View Post
    I always say that if you do PV you have to stand on your head when you read the electrical code.
    Okay, hold on a sec. I think I found something that might help me, but you solar dudes gotta talk real sloooowwwly so I can try and keep up.

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    "Electricity is really just organized lightning." George Carlin


    Derek

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    Quote Originally Posted by jaggedben View Post
    So I'm installing a system with two high voltage LG batteries and it appears I need to use a fused combiner to parallel them. Max voltage for each battery unit is 570V. 'Peak current' is 18.9A but no short circuit current rating is listed. The circuit is ungrounded. A battery combiner is a first for me, and I have some questions:

    Under the 2014 NEC...

    - For two batteries, would a battery combiner be required by the Code if not required by the manufacturer, if all wiring were sized to handle current from both batteries?
    - Under the 2014 NEC, would you say both positive and negative need to be fused, or just one side (i.e. positive)?
    - Does the code require such a combiner to be listed?

    Opinions wanted. There doesn't seem to be much code guidance on this in the 2014, or even the 2017.
    Interesting. I need some education on ESS installation myself.

    1. Is not the LG product intended to be installed only on a 1-1 ratio (matched components) with a compatible DC coupled inverter like StorEdge?
    2. The DC output from the LG ESS battery pack appears to be protected with overcurrent protection in the battery pack...as required by 690.71(C) of the 2014 NEC and 706.21(D) of the 2017 NEC.
    3. Under the 2014 NEC, the AHJ would have discretion on allowing unlisted equipment. Section 706.5 in Article 706 of the 2017 NEC calls for listing of ESS equipment.

    My Opinion-Comments on your questions...

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    Quote Originally Posted by shortcircuit2 View Post
    Interesting. I need some education on ESS installation myself.

    1. Is not the LG product intended to be installed only on a 1-1 ratio (matched components) with a compatible DC coupled inverter like StorEdge?
    Two batteries can be connected to the newer version of the StorEdge. Not more than two. The product literature is a bit vague on how, I should probably just contact LG and SolarEdge.

    2. The DC output from the LG ESS battery pack appears to be protected with overcurrent protection in the battery pack...as required by 690.71(C) of the 2014 NEC and 706.21(D) of the 2017 NEC.
    Right, but I haven't been able to determine the rating of that overcurrent protection. And that doesn't necessarily protect the paralleled wiring. But I do feel that if all the wiring is rated for the sum of the OCPD rating, then additional overcurrent protection is redundant.

    3. Under the 2014 NEC, the AHJ would have discretion on allowing unlisted equipment. Section 706.5 in Article 706 of the 2017 NEC calls for listing of ESS equipment.

    My Opinion-Comments on your questions...
    Thanks.

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    Quote Originally Posted by jaggedben View Post
    Two batteries can be connected to the newer version of the StorEdge. Not more than two. The product literature is a bit vague on how, I should probably just contact LG and SolarEdge.
    I see that stacking 2 batteries is new. Let us know what you find out.

    Thanks

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    Update...

    SolarEdge does not require a fused combiner. They said they thought LG required it.

    LG seemed a little confused by the question. On the phone when I asked if a fused combiner was required I was told 'yes', but in a follow up email they stated that a junction box or combiner must be supplied, and that fuses are not required because the batteries contain their own circuit breakers. And yet they also recommended two fused combiner products. Based on the email I'm assuming I can just combine in a j-box with no fuses.

    So in that case, what do my wires needed to be rated for? Here's my thinking:

    There is no short circuit current rating on the data sheet. Conservatively I'd use the 25A rating of the internal circuit breaker for that. Alternatively I could use the peak current in the installation manual of 18.9A, but that doesn't exactly jive with Article 240.

    Now, is a continuous use factor required? My thought is only for the operating current, which is listed as 14.3A (discharging). The peak current rating is listed as 'for 10 sec' so that's not continuous. So if using the 25A breaker rating, I do not need a continuous use factor.

    Conclusion: use 8AWG for all battery wiring since it's rated for 50A and that's the sum of the two 25A breakers.

    (In reality 10awg is probably safe since output current is controlled by communication with the inverter and they are supposed to charge and discharge at separate times. But per the NEC I can't really say 10awg is protected by two 25A breakers.)

    Anybody think I'm missing anything?

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