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Parallel outputs of AC disconnects to load-side tap

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  • pv_n00b
    replied
    HiQ inverters combine in an AC junction box, with no OCPD, and then the combined output goes to a common CB in an AC combiner panel. No problem doing it, just size all the conductors correctly. But they do have the OCPD at the AC combiner where you just have a tap. But since you are tapping after the main CB it should count as the supplying OCPD.

    The conductors between each switch and the common tie point are subject to the fault current back feed from the service and from the other inverter, most people don't size for this and just size it for the inverter output. For this system it would be sized for 300A.
    Last edited by pv_n00b; 10-25-16, 10:34 PM.

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  • jaggedben
    replied
    Your AHJ could say just about anything about this, especially if you're still on the 2011 code. But I think it's a safe installation.

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  • shortcircuit2
    replied
    Originally posted by deadshort View Post
    -My main question was concerning the combining of the AC disco outputs to the tap. As long as the conductors from the discos to the tap are rated for 200A we should be good right?
    Yes.

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  • deadshort
    replied
    Originally posted by jaggedben View Post
    FWIW, under the current CA code (2011 NEC equivalent), you just have to ask your AHJ about load side taps. Some may recognize that the current code doesn't adequately address the situation and let you use the 2014 code rules. Some may allow you to load the feeder to 120% per 705.12(D)(2). (That would not be applicable in the OPs case). Others will just say no.
    Hi guys, sorry for the delay. Long weekend. Anyways, yes, I am in CA (Don't hold it against me).

    To clarify a couple points: We are tapping into 4/0 feeders with piercing connectors.
    -The loads at the other end of the 4/0 feeder are in a panel protected by a 200A main
    -We have to arrange the PV this way to distribute to different meters for (billing/cost purposes?) instead of consolidating it (Don't ask me, I'm not the sales/money guy).
    -My main question was concerning the combining of the AC disco outputs to the tap. As long as the conductors from the discos to the tap are rated for 200A we should be good right?

    It's just a weird setup we've never tried before and is open to interpretation.

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  • jaggedben
    replied
    FWIW, under the current CA code (2011 NEC equivalent), you just have to ask your AHJ about load side taps. Some may recognize that the current code doesn't adequately address the situation and let you use the 2014 code rules. Some may allow you to load the feeder to 120% per 705.12(D)(2). (That would not be applicable in the OPs case). Others will just say no.

    Leave a comment:


  • Smart $
    replied
    Originally posted by jaggedben View Post
    In 2.5 months. You asked me what code, I told you, and it's not 100% clear where the OPs project is anyway.
    The location is not 100% clear, but I'm leaning heavily toward CA.

    I asked the question within the context of in-effect CA Code.

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  • jaggedben
    replied
    Originally posted by Smart $ View Post
    You guys (CA) on 2014 now?
    In 2.5 months. You asked me what code, I told you, and it's not 100% clear where the OPs project is anyway.

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  • zman990
    replied
    It wouldn't be 280 amps my mistake still 240amps because max backfeed in gear is 240

    Sent from my SAMSUNG-SM-N920A using Tapatalk

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  • zman990
    replied
    Instead of tapping the gear is possible to change the the subpanel bus rating by simply retrofitting the sub panel to a MLO 400 amp bus with a 200 amp main breaker in the gear. Giving you 280A of inverter output rating you only need 200 so if one of those sub panels are close to you disconnect change it and put a backfeed breaker in sub panel.
    Use same manufacturer for current subpanel to save money on breakers anything can be made make sure the conductors are good for 200 amps between gear breaker and new MLO sub panel.




    Sent from my SAMSUNG-SM-N920A using Tapatalk

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  • Smart $
    replied
    Originally posted by jaggedben View Post
    Here is what the OP said in post #1:


    ..and that is allowed under the 2014 code.
    You guys (CA) on 2014 now?

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  • jaggedben
    replied
    Originally posted by Smart $ View Post

    If it's being planned as a load-side connection, what Code are you going to use to connect 200A of PV to a 200A bus with loads?
    Here is what the OP said in post #1:
    ... tapped into a 4/0 feeder between an existing 200A main breaker and a remote load center (also protected by a 100A main).
    ..and that is allowed under the 2014 code.

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  • shortcircuit2
    replied
    Originally posted by jaggedben View Post
    Not sure why you'd say that. Why can't they follow the tap rules?
    1. The taps as depicted in the diagram don't meet any tap requirements.

    2. The tap feeds 2-100amp fusible disconnects with what appears to be significant PV outputs given that it shows a 40amp & 60amp overcurrent device in each sub-panel.

    Without more detailed information from the OP, we can only guess. His tap may be sized for 200amps. He doesn't specify this.

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  • Smart $
    replied
    Originally posted by jaggedben View Post
    ...The diagram and description says there's a load off the main. Whether it can be done depends on code cycle and some amount of interpretation.
    The diagram says "TO LOADS" after service disconnect, but the bottom two show connected panels, i.e. loads, whereas the top disconnect has only the PV system shown. I see that as being being enough to call into question whether this is a supply- or load-side connection.

    If it's being planned as a load-side connection, what Code are you going to use to connect 200A of PV to a 200A bus with loads?

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  • jaggedben
    replied
    Originally posted by deadshort View Post
    Is it okay to parallel the outputs of AC disconnects and run one feeder into a load-side tap?

    2 separate sub panels with identical inverter breakers (100A total each) would be fed into their own respective 100A AC discos.

    After the discos the two circuits would be combined with an insulated connector and one conductor would be tapped into a 4/0 feeder between an existing 200A main breaker and a remote load center (also protected by a 100A main).

    This idea was proposed but I've never seen it done before and it just seemed weird to me and I'm having trouble wrapping my head around it.

    Would different inverter output currents have any sort of negative effect? The current should just add right? Is this even viable/allowed by code? Can't find anything specific in 310.4 for source circuits.

    Thanks in advance.
    Why not put main breakers in the subpanels? Why do the two subpanel circuits need to be combined remotely from the tap? Why not aggregate everything in one sub as suggested by shortcircuit? If there have to be two subpanels and they have to be combined remotely, why not do it with a third sub containing an main breaker? That way you'd have a simple one circuit tap.

    All those questions aside, if this is in California, then the whole concept of a load side tap is questionable under the current code. In three months when we're on the 2014 NEC equivalent then I don't see an issue. The remote load center being served by the existing feeder does need to have that main breaker installed per 705.12(D)(2)(1)(b). (Is it really a 100A, or did you make a typo?)


    Originally posted by shortcircuit2 View Post
    The feeder conductors to the 100amp fusible disconnects would need to be rated for the 200amp overcurrent device at the service.
    Not sure why you'd say that. Why can't they follow the tap rules?

    Originally posted by Smart $ View Post
    Are there loads off the main, or is the PV system all that is connected to that main (as depicted)?
    ...
    If there are loads off the main, it can't be done.
    The diagram and description says there's a load off the main. Whether it can be done depends on code cycle and some amount of interpretation.

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  • shortcircuit2
    replied
    The feeder conductors to the 100amp fusible disconnects would need to be rated for the 200amp overcurrent device at the service.

    Then the existing 200amp service feeder must feed a sub-panel down stream. It would now need a 200-amp breaker ahead of it because it could draw 200 from the utility and what ever the output of the solar is.

    No problem with the multiple inverter outputs. Current will add.

    Why not just combine it all into one aggregation panel after the load side feeder connection?

    Leave a comment:

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