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  1. #11
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    Quote Originally Posted by codequestion View Post
    What you talking about? 690.9 says overcurrent protection required at pv source circuit?

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    Not at the modules though. If you parallel source circuits together and there is more fault current available to a faulted source circuit than it is rated for, either the conductor or the module, then OCP is required in the DC combiner, or in the harness if that is being used to parallel source circuits. OCP is usually required whenever you parallel more than 2 source ckts, but it was not always that way. There was a time when the series fuse rating of some modules was much larger than the Isc value. At that time you could parallel 3, 4, or more source circuits without OCP. Those days are gone though.
    Last edited by pv_n00b; 06-06-18 at 11:56 PM.

  2. #12
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    Quote Originally Posted by jaggedben View Post
    Also: don't be mislead by pv_noob's handle, he's probably the most experienced regular PV poster on this forum.
    I defend my total and complete n00bness. I have no idea why people listen to me.

  3. #13
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    Quote Originally Posted by codequestion View Post
    So if I have 3 solar panels, each panel made up of 14 modules lets say and each panel their is y feeder cables going to junction box. Total going into junction box 3*y and other side of junction box same number of cables 3*y come out and feed inverter then which is my pv source circuit and pv output circuit? Do i need overcurrent protection between panel and junction box?

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    Passthru junction boxes do not combine the circuits, so PV source ckts in, PV source ckts out. A PV system is not required to have a PV output ckt, it can be source ckts all the way down.

  4. #14
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    Quote Originally Posted by pv_n00b View Post
    Not at the modules though. If you parallel source circuits together and there is more fault current available to a faulted source circuit than it is rated for, either the conductor or the module, then OCP is required in the DC combiner, or in the harness if that is being used to parallel source circuits. OCP is usually required whenever you parallel more than 2 source ckts, but it was not always that way. There was a time when the series fuse rating of some modules was much larger than the Isc value. At that time you could parallel 3, 4, or more source circuits without OCP. Those days are gone though.
    Are you sure? Last I checked there were some high V low I thin films modules with max series fuse ratings high enough to allow you to combine more than 2 strings.

  5. #15
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    Quote Originally Posted by ggunn View Post
    Are you sure? Last I checked there were some high V low I thin films modules with max series fuse ratings high enough to allow you to combine more than 2 strings.
    I have not run across on in a while, feel free to point me toward any you know. Thin film did have the highest series fuse verses Isc ratios in the past. The thin film modules I have seen lately though have low series fuse ratings. Take the FirstSolar series 6, it has a series fuse rating of 6A. So to put three strings in series the Isc of each string would have to be less than 6/1.25/2= 2.4A and all the series 6 Isc values are 2.54A or more.

    I'm not sure why this is the case. The series fuse value is given to the NRTL by the module manufacturer and the NRTL tests that the module can support that amount of reverse current. It's not like the NRTL determines the fuse value through testing and gives it to the manufacturer. So the module could be designed to support a higher reverse current. Most likely it's cheaper to design to the lowest reverse current possible.

  6. #16
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    Quote Originally Posted by pv_n00b View Post
    I have not run across on in a while, feel free to point me toward any you know. Thin film did have the highest series fuse verses Isc ratios in the past. The thin film modules I have seen lately though have low series fuse ratings. Take the FirstSolar series 6, it has a series fuse rating of 6A. So to put three strings in series the Isc of each string would have to be less than 6/1.25/2= 2.4A and all the series 6 Isc values are 2.54A or more.

    I'm not sure why this is the case. The series fuse value is given to the NRTL by the module manufacturer and the NRTL tests that the module can support that amount of reverse current. It's not like the NRTL determines the fuse value through testing and gives it to the manufacturer. So the module could be designed to support a higher reverse current. Most likely it's cheaper to design to the lowest reverse current possible.
    I haven't seen one lately, but then, I haven't looked. I just wanted to point out that the NEC doesn't specify that more than two parallel strings must be fused, just that the available fault current in paralleled unfused strings must not exceed the maximum module fuse rating.

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