Page 1 of 2 12 LastLast
Results 1 to 10 of 16

Thread: Difference between two

  1. #1
    Join Date
    Jul 2017
    Location
    MD, USA
    Posts
    628

    Difference between two

    What is the difference between PV source circuit and PV output circuit? Also, does anyone have clear schematic or diagram besides the one shown in nec 2014?

    Sent from my SM-G935U using Tapatalk

  2. #2
    Join Date
    Nov 2015
    Location
    CA, USA
    Posts
    575
    When PV source and output circuits were defined in the early versions of 690 it was to allow the code to specify where OCP was needed and more specifically where it was not needed. AHJs wanted to put fuses in every string at the modules because many people did not understand the current limiting quality of PV modules. To keep AHJs from requiring OCP at the modules PV source circuits were defined and the code specified that OCP was not required. So that's how it started.

    It's more complex now. If there is a wiring harness that combines strings in the harness is that still a PV source circuit? If there are DC to DC converters at the module or string level is it still a PV source circuit? If a DC to DC converter takes in several strings and has only one output conductor is that output a PV output circuit? There are differing interpretations. I think at his point making the distinction is an anachronism that just makes working with the PV DC circuits more difficult.

    My interpretation is according to a strict reading of the NEC, once two or more PV source circuits are combined at a common connection point that point represents the transition from PV source circuits to a PV output circuit. This still does not deal with the issue of a DC to DC converter that takes in multiple source circuits and outputs one circuit. Is it really a common connection point when going through the electronics? If there can't be any back feed then I would say not.

  3. #3
    Join Date
    Jul 2017
    Location
    MD, USA
    Posts
    628
    What you talking about? 690.9 says overcurrent protection required at pv source circuit?

    Sent from my SM-G935U using Tapatalk

  4. #4
    Join Date
    May 2011
    Posts
    4,401
    Quote Originally Posted by codequestion View Post
    What is the difference between PV source circuit and PV output circuit? Also, does anyone have clear schematic or diagram besides the one shown in nec 2014?
    Short answer: it's a source circuit until you parallel it with another source circuit. The output of two or more paralleled source circuits is an output circuit.

    Quote Originally Posted by codequestion View Post
    What you talking about? 690.9 says overcurrent protection required at pv source circuit?
    Not really. See the exceptions. What it comes down to is that overcurrent protection isn't required unless you have more than two paralleled circuits, or different circuit current values. Single source circuits don't require overcurrent protection because PV modules can't realistically produce an overcurrent.

    Also: don't be mislead by pv_noob's handle, he's probably the most experienced regular PV poster on this forum.

  5. #5
    Join Date
    Jul 2017
    Location
    MD, USA
    Posts
    628
    Quote Originally Posted by jaggedben View Post
    Short answer: it's a source circuit until you parallel it with another source circuit. The output of two or more paralleled source circuits is an output circuit.



    Not really. See the exceptions. What it comes down to is that overcurrent protection isn't required unless you have more than two paralleled circuits, or different circuit current values. Single source circuits don't require overcurrent protection because PV modules can't realistically produce an overcurrent.

    Also: don't be mislead by pv_noob's handle, he's probably the most experienced regular PV poster on this forum.
    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?

    Sent from my SM-G935U using Tapatalk

  6. #6
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
    Posts
    9,777
    Quote Originally Posted by jaggedben View Post
    Short answer: it's a source circuit until you parallel it with another source circuit. The output of two or more paralleled source circuits is an output circuit.



    Not really. See the exceptions. What it comes down to is that overcurrent protection isn't required unless you have more than two paralleled circuits, or different circuit current values. Single source circuits don't require overcurrent protection because PV modules can't realistically produce an overcurrent.

    Also: don't be mislead by pv_noob's handle, he's probably the most experienced regular PV poster on this forum.
    I couldn't put my finger on the code reference, but I'm pretty sure it allows for the unfused combination of more than two strings as long as the available fault current is less than the rating of the maximum series fuse allowed by the modules.

    And what am I, chopped liver?

  7. #7
    Join Date
    Jul 2017
    Location
    MD, USA
    Posts
    628
    Okay well i dont know what code section that you are mentioning either. Chopped liver?
    Quote Originally Posted by ggunn View Post
    I couldn't put my finger on the code reference, but I'm pretty sure it allows for the unfused combination of more than two strings as long as the available fault current is less than the rating of the maximum series fuse allowed by the modules.

    And what am I, chopped liver?
    Sent from my SM-G935U using Tapatalk

  8. #8
    Join Date
    Oct 2009
    Location
    Austin, TX, USA
    Posts
    9,777
    Quote Originally Posted by codequestion View Post
    Okay well i dont know what code section that you are mentioning either. Chopped liver?

    Sent from my SM-G935U using Tapatalk
    I remember going through this exercise a year or so ago, and I found that it was possible with high voltage, low current thin films modules one could legally combine three strings without fuses.

    Found it. In the 2014 NEC it's 690.9(A) Exception (b).

  9. #9
    Join Date
    May 2011
    Posts
    4,401
    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?
    The wires going to the panels are the source circuits. The combined output connecting to the inverter is the output circuit.

    Btw, the code definition for 'panel' does not describe a real world object these days. Sorry for the confusion. We arrange modules electrically into strings, which are the same as source circuits (unless you have optimizer or microinverters). What the code calls modules is what lay people call panels.

    Overcurrent requirement protection depends on further details, see other posts.

  10. #10
    Join Date
    May 2011
    Posts
    4,401
    Quote Originally Posted by ggunn View Post
    I remember going through this exercise a year or so ago, and I found that it was possible with high voltage, low current thin films modules one could legally combine three strings without fuses.

    Found it. In the 2014 NEC it's 690.9(A) Exception (b).
    I would say if you've got modules that have a fuse rating that's s bit more than twice their short circuit current rating, you could probably do 3 strings with no fuses. I'm not so surprised you found a thin film module like that, but I'd be surprised to see a silicon module that qualified.

    And yes, you're chopped liver. My excuse is I did say 'probably' re pv_noob. You and he can throw down if you want.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •