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Thread: Differences between data sheet and the calculation.

  1. #11
    Join Date
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    san jose, Costa Rica, code NEC USA
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    Quote Originally Posted by ggunn View Post
    Are you sure about that? I just went through a slew of inverter data sheets and not one of them specifies a maximum AC OCPD. I cannot see how or why an inverter company or UL would care about such a thing. We routinely interconnect inverters through OCPD 3X or more the maximum inverter current for various reasons.

    But in the event an inverter company specifies a max OCPD for some reason I guess you have to comply in order not to void their warranty. Stupid, IMO.
    Well,


    In my case, because I have to take into account the voltage drop, I have increased the wire size to 4/0, so it is fine for 225A protection. but as pv_n00b says, I'm not going to to worry about this anymore.


    Thanks for your support.


    Regards,

  2. #12
    Join Date
    Sep 2012
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    Clinton, WA
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    90
    Most of the residential inverters I work with (SMA, Solectria, SolarEdge, Fronius) specify a max OCPD on the AC side. This is generally found in the installation manual, but not the spec sheet. The max OCPD specified in the manual is often larger than the minimum OCPD calculated per the NEC. For instance, the SolarEdge HD Wave inverters from 3.0 kW to 7.6 kW all have a max OCPD of 50A. When installing a 3.0 kW inverter with a max rated AC current of 16.5A, the installer has the option to install a 20A, 25A, 30A, 35A, 40A, 45A, or 50A breaker.

  3. #13
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    May 2013
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    Massachusetts
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    Quote Originally Posted by INGMRS View Post
    Well,


    In my case, because I have to take into account the voltage drop.
    Voltage drop is one reason you might want to strategically increase the OCPD size to larger than what you need, if allowable. As an example, suppose you have a circuit which would ordinarily be a 30A breaker with #10 Cu wire & #10 Cu EGC. If you need to use a #6 Cu wire to curtail voltage drop, and keep the 30A OCPD, this would mean a #6 Cu EGC. However, if you can use a 60A OCPD, then #6 Cu is already the starting point size, and there's no need to upsize beyond the #10 Cu EGC. It's counterintuitive that you can do this, but it is what the NEC allows, should your inverter manual also allow it.

  4. #14
    Join Date
    Nov 2015
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    Quote Originally Posted by ggunn View Post
    Are you sure about that? I just went through a slew of inverter data sheets and not one of them specifies a maximum AC OCPD. I cannot see how or why an inverter company or UL would care about such a thing. We routinely interconnect inverters through OCPD 3X or more the maximum inverter current for various reasons.

    But in the event an inverter company specifies a max OCPD for some reason I guess you have to comply in order not to void their warranty. Stupid, IMO.
    Yup, I'm sure. Some inverter manufacturers of central inverters include an internal OCPD that satisfies the requirement and then will not have to specify an external OCPD rating. But if they don't then the external OCPD max rating has to be given. It's almost never listed on the data sheet but is in the installation manual somewhere, usually in the section on AC interconnection. If it's not given somewhere then the NRTL that listed the equipment failed to verify the documentation.

    It's necessary to limit the fault current into an inverter in the event there is an internal fault. If the fault current exceeds the inverter containment rating then the box could let the fire out during a fault. So if you have been exceeding the manufacturer supplied max OCPD rating you have been creating unsafe conditions in your installations. Not good.

  5. #15
    Join Date
    Oct 2009
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    Austin, TX, USA
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    Quote Originally Posted by pv_n00b View Post
    Yup, I'm sure. Some inverter manufacturers of central inverters include an internal OCPD that satisfies the requirement and then will not have to specify an external OCPD rating. But if they don't then the external OCPD max rating has to be given. It's almost never listed on the data sheet but is in the installation manual somewhere, usually in the section on AC interconnection. If it's not given somewhere then the NRTL that listed the equipment failed to verify the documentation.

    It's necessary to limit the fault current into an inverter in the event there is an internal fault. If the fault current exceeds the inverter containment rating then the box could let the fire out during a fault. So if you have been exceeding the manufacturer supplied max OCPD rating you have been creating unsafe conditions in your installations. Not good.
    When we are designing with microinverters the maximum number of inverters on a branch is 12 @1.33A per, which maxes out a 20A OCPD, but we interconnect with a 20A breaker whether the inverter count is 12 or 1. Also, if it were a safety issue, you'd think the inverter companies would display it more prominently than burying it somewhere in a manual.

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