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Thread: Solar edge string fuses

  1. #11
    Join Date
    Jul 2009
    Mesa Arizona
    With SolarEdge you have series strings of Optimizers, not series strings of PV modules.

    The SE9KUS has two DC inputs on a terminal strip (the two input strings are parallel connected at the input terminal), each terminal position is usually used for a series string of Optimizers. The datasheet shows 'Maximum Input Voltage DC+ to DC-' is 500 VDC and 'Maximum Input Current' is 26.5A. Maximum DC Power (Module STC) is shown as 12,150W.

    The datasheet for the P320 Optimizer shows that for THREE PHASE 208V 'Minimum String Length (Power Optimizers)' is 10, 'Maximum String Length' is 25, and 'Maximum Power per String' is 6000W. Maximum Output Current is 15A.

    The original post does not identify the PV module rated power, but if it is 300W or less there would be no problem connecting one string of 20 and one string of 19 Optimizers to the inverter. No fuses required. If the PV modules are over 300W each, there is a problem.

    The discussion at a SolarEdge training session was that the inverter will adjust the outputs of the Optimizers such that the inverter input current, 26.5A in this case, is not exceeded.

    The installation instructions do state "You can connect systems with multiple DC strings in parallel to the DC input terminals of the switch. Inverters have one, two or three pairs of DC input terminals, depending on the inverter power rating. If more strings are required, they can be connected in parallel using an external combiner box before connecting to the switch." These are strings of Optimizers and the rules based on PV module ISC and related fuse requirements do not apply, but the output current of the Optimizers must be considered for wire sizing. If fuses are used to reduce wire gauge for each string, they are based on the continuous 15A of the Optimizer, 20A in this case and the 20A is used for calculation of the required wire gauge as generally done.

  2. #12
    Join Date
    Nov 2015
    CA, USA
    Quote Originally Posted by ggunn View Post
    I sent that document to our local AHJ and his response was that he is not going to take SolarEdge's word for it. He wants to see something from an independent testing lab.
    Unfortunately, this is not a test in UL 1741 and I doubt SE is going to have an NRTL run an independent test to demonstrate how it works ($$$$).

    Quote Originally Posted by SunFish View Post
    SolarEdge also has a letter from Bill Brooks on this subject floating out there somewhere. If you contact their tech support they should be able to send you a copy.
    Bill must think AHJs roll over after seeing anything with his name on it. I've seen the letter, it makes a good argument for the safety of the SE system and how SE complies with the spirit of the NEC without complying with the text. As good a description as I have seen in this thread. It's basically a request for an AM&M exemption from the AHJ. Maybe an AHJ will accept it, maybe not. Find out before you install anything because the rework will cost you.

  3. #13
    Join Date
    Oct 2009
    Austin, TX, USA
    Quote Originally Posted by pv_n00b View Post
    Unfortunately, this is not a test in UL 1741 and I doubt SE is going to have an NRTL run an independent test to demonstrate how it works ($$$$).
    I know, and that's why we put in string fusing when we have to use three strings in most (all?) jurisdictions. Choose your battles.

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