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Thread: high voltage battery combiner

  1. #11
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    Quote Originally Posted by jaggedben View Post
    Update...SolarEdge does not require a fused combiner. They said they thought LG required it.
    Hmmm...SE seems to always avoid situations that will add cost to their systems.

    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.
    If the 2 battery packs are stacked or paralleled like PV strings, will a short in the output of 1 of the battery pack outputs feed into the short like in PV strings?

    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.
    Can you give a link to specs on the LG product? Are we looking at the RESU10H with the SE StorEdge?

    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.
    I need to think about this.

  2. #12
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    I think you have it covered pretty well. Batteries tend to have large fault currents, limited only by the voltage and internal resistance of the battery. You would definitely want an OCPD in the string and it sounds like LG has provided one in the pack. Since the conductors are protected by the OCPD in the battery pack you want to make sure they are sized to be protected by that as well as carry the load current.

    Personally, I don't think we need to use 1.25*Imax to size the conductor unless the battery is rated to supply Imax for more than 3 hours. Most are not. So sizing the conductor is a two-part process. Get the 3-hour current rating (I3hr) from the manufacturer and Imax. Find the size of the conductor for 1.25*I3hr and for Imax and use the larger conductor.

  3. #13
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    Quote Originally Posted by shortcircuit2 View Post
    If the 2 battery packs are stacked or paralleled like PV strings, will a short in the output of 1 of the battery pack outputs feed into the short like in PV strings?
    Yes, but all of it would be on the same side of the batteries' internal circuit breakers.

    If I had one battery, I would use 10awg CU and be protected by the 25A breaker.

    If I use a fused combiner, I would use 10awg between each battery and combiner, and 8awg between the combiner and the inverter.

    If I don't use a fused combiner, I use 8awg for all the wiring. This is cheaper and easier and I don't see anything unsafe about it.

    The same principle has been applied to two PV strings for as long as I can remember, except that because PV strings are current limited we actually can use the short circuit rating (*1.56) instead of an OCPD.

  4. #14
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    Quote Originally Posted by pv_n00b View Post
    I think you have it covered pretty well. Batteries tend to have large fault currents, limited only by the voltage and internal resistance of the battery. You would definitely want an OCPD in the string and it sounds like LG has provided one in the pack. Since the conductors are protected by the OCPD in the battery pack you want to make sure they are sized to be protected by that as well as carry the load current.

    Personally, I don't think we need to use 1.25*Imax to size the conductor unless the battery is rated to supply Imax for more than 3 hours. Most are not. So sizing the conductor is a two-part process. Get the 3-hour current rating (I3hr) from the manufacturer and Imax. Find the size of the conductor for 1.25*I3hr and for Imax and use the larger conductor.
    Thanks for the response. Yes, the 3hr current rating is 14.3A, mentioned above. (Actually, that's for any time more than 10sec.) There is no Imax listed. The 25A breaker rating is not listed on the datasheet but I have now seen it on the breaker in person. I tend to think that any internal potential Imax over 25A is moot because of the breaker. Keep in mind this is not just a bunch of cells wired up, it's an integrated pack with a BMS and other internal electronic controls.

  5. #15
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    Quote Originally Posted by jaggedben View Post

    If I use a fused combiner, I would use 10awg between each battery and combiner, and 8awg between the combiner and the inverter.

    If I don't use a fused combiner, I use 8awg for all the wiring. This is cheaper and easier and I don't see anything unsafe about it.
    You may want (need) to use the fused combiner. In looking at 706.21(A) of the 2017 Code...ESS circuit conductors shall be protected in accordance with the requirements of Article 240.

    240.15(A) requires OC protection in each ungrounded conductor and 240.21 requires OC protection at the point where the conductor receives its supply.

    So at the point where the ESS outputs are combined, OC protection is needed...IMO

    I didn't review the 2014 on this, but I believe the same rules apply.

  6. #16
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    Quote Originally Posted by shortcircuit2 View Post
    You may want (need) to use the fused combiner. In looking at 706.21(A) of the 2017 Code...ESS circuit conductors shall be protected in accordance with the requirements of Article 240.

    240.15(A) requires OC protection in each ungrounded conductor and 240.21 requires OC protection at the point where the conductor receives its supply.

    So at the point where the ESS outputs are combined, OC protection is needed...IMO

    I didn't review the 2014 on this, but I believe the same rules apply.
    Well, 706 is a new article that didn't even exist in the 2014.

    Is a paralleling location a 'point of supply'? I think my argument would be that the batteries are the point of supply. Or at any rate, that if all the conductors are protected from the maximum possible current then more OCPD at the point of paralleling would be redundant.

  7. #17
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    Quote Originally Posted by jaggedben View Post
    Thanks for the response. Yes, the 3hr current rating is 14.3A, mentioned above. (Actually, that's for any time more than 10sec.) There is no Imax listed. The 25A breaker rating is not listed on the datasheet but I have now seen it on the breaker in person. I tend to think that any internal potential Imax over 25A is moot because of the breaker. Keep in mind this is not just a bunch of cells wired up, it's an integrated pack with a BMS and other internal electronic controls.

    By Imax I mean the maximum current the battery can supply under maximum load, not the fault current. It might be listed as the surge current or something similar and with a 25A CB could be up to 25A. Since storage is new there are still issues about what information is needed from the manufacturer to integrate their product into a complete design. Until it's worked out we just have to ask for the information we need if it does not show up on the data sheet.

  8. #18
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    Quote Originally Posted by shortcircuit2 View Post
    You may want (need) to use the fused combiner. In looking at 706.21(A) of the 2017 Code...ESS circuit conductors shall be protected in accordance with the requirements of Article 240.

    240.15(A) requires OC protection in each ungrounded conductor and 240.21 requires OC protection at the point where the conductor receives its supply.

    So at the point where the ESS outputs are combined, OC protection is needed...IMO

    I didn't review the 2014 on this, but I believe the same rules apply.

    I think that having an OCPD in the battery would provide the protection called out in 706.21(A) and 240 for the output conductors. Putting two battery strings in parallel with OCPD on the battery end does not expose either conductor to additional overcurrent. The addition of OCPD in the combiner adds no additional protection, it justs puts the same rated OCPD in series.

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