Results 1 to 9 of 9

Thread: equipment grounding conductor

  1. #1
    Administrator
    Join Date
    Feb 2011
    Location
    Annapolis Md
    Posts
    6,134

    Default equipment grounding conductor

    I just wanted to run this by the local EE here
    We installed a ground mount array in which there are two array's and two inverters.
    The distance from the array's to the inverters and service is 400'
    We used initially 2 #2 AL USE direct burial cable for current carrying conductors and a #4 for the EGC. for each array
    The inspector made us replace the ECG with a #2 but only one conductor.
    All bonding and grounding takes place at the array as we have 28 pipes buried in concrete and 2 ground rods driven at the array.
    So my question is thus
    What purpose does the ECG serve in addition to the bonding and grounding at the array.
    The sizing of the conductor is based on article 250 that states that grounding conductors shall be the same size as current carrying conductors in circuits under 30A
    In Article 690.43 states that ECG do not have to be increased in size to compensate for voltage drop which is the case here. and minimum size is #14.
    I know the AHJ is always right.

  2. #2
    Solar Fanatic
    Join Date
    Feb 2010
    Posts
    11,542

    Default

    Quote Originally Posted by Naptown View Post
    What purpose does the ECG serve in addition to the bonding and grounding at the array?
    The primary purpose of any EGC is to provide a planned path to operate over current protection device like breakers and fuses. Do not confuse that with ground, they are not the same thing

    Quote Originally Posted by Naptown View Post
    The sizing of the conductor is based on article 250 that states that grounding conductors shall be the same size as current carrying conductors in circuits under 30A
    Correct per 250.22

    Quote Originally Posted by Naptown View Post
    In Article 690.43 states that ECG do not have to be increased in size to compensate for voltage drop which is the case here. and minimum size is #14.
    I know the AHJ is always right.
    Correct on both accounts. The AHJ is inexperienced and wins the argument. It is a simple case of you do what he wants. It will cost you more in delays, repeat trips, and inspection fees to fight it. It will cut into your bottom line, it suks, and is over kill, but it is safe and you can sleep well tonight to fight another day. Next job factor it in if you think you are getting the same AHJ.

    Another approach is build a relationship with the inspector. Try lunch sometime at your expense. Talk shop. Both of you might learn something from each other like respect. He may learn he needs to brush up on 690, or you may learn there is a local amendment to 690. Either way you both walk away better for it.
    MSEE, PE

  3. #3
    Administrator
    Join Date
    Feb 2011
    Location
    Annapolis Md
    Posts
    6,134

    Default

    I knew you were going to say that.
    In this case it was no big deal as it was an open trench. Last time it was a vibra plow install and tearing it out and replacing was a bit of a pain.
    They are also requiring voltage drop calculations on the DC side. No big deal it is under 1.5%
    But getting back to grounding. On a normal roof mount on the same building I would ground the inverter and bond the racking and modules and run everything to the building ground.
    I was under the impression (perhaps wrong) that on a remote ground mounted array that it could be grounded at the array and not run back to the main service. In this case we bonded and grounded with #6 copper at the array. The bond did not run back to the service ground. they seem to be OK with that.

  4. #4
    Solar Fanatic
    Join Date
    Feb 2010
    Posts
    11,542

    Default

    Rich didn't you run up against this a few months back. I think we spoke on the phone about it.

    Anyway if this was a Service Entrance you would be right. However it is not, it is a feeder and you are still right. What the inspector is worried about is if one of the high voltage DC conductors at the house became faulted to ground, there is no path for return current to operate an OCPD.

    Lastly does your jurisdiction use NEC as written or do they have local amendments modifying the NEC. That might be where he is dinging you. My educated guess is they amended 690.43 and replaced it with 250 requirements. Either that or the inspector is not familiar with 690.43

    Your local permitting agency should have a list of amendments, if they do have them, available on the web.
    MSEE, PE

  5. #5
    Administrator
    Join Date
    Feb 2011
    Location
    Annapolis Md
    Posts
    6,134

    Default

    Inverters are grounded, bonded and have internal ground fault protection and detection. they are mounted inside the house.

  6. #6
    Solar Fanatic
    Join Date
    Feb 2010
    Posts
    11,542

    Default

    Quote Originally Posted by Naptown View Post
    Inverters are grounded, bonded and have internal ground fault protection and detection. they are mounted inside the house.
    Rich I understand that part, no problem.

    I am assuming from the ground mounts 400 feet away it is high voltage DC going to the house?

    If that is the case then there are to ways to provide over current protection.

    • One is to bond one of the polarities at the array, and run an EGC with them to the house.
    • Two is you are still required to bond at the array, but DO NOT RUN an EGC to the house but instead bond one polarity again at the house to ground. Just like you would any standard AC service. PCO does not run a ground with the service, customer has to provide that.
    MSEE, PE

  7. #7
    Administrator
    Join Date
    Feb 2011
    Location
    Annapolis Md
    Posts
    6,134

    Default

    Quote Originally Posted by Sunking View Post
    Rich I understand that part, no problem.

    I am assuming from the ground mounts 400 feet away it is high voltage DC going to the house?

    correct

    If that is the case then there are to ways to provide over current protection.

    There are combiners with fuses at the array and fuses in the inverter on the DC side
    • One is to bond one of the polarities at the array, and run an EGC with them to the house.
    • Wouldn't that defeat the ground fault protection in the inverter?
    • Two is you are still required to bond at the array, but DO NOT RUN an EGC to the house but instead bond one polarity again at the house to ground. Just like you would any standard AC service. PCO does not run a ground with the service, customer has to provide that.

      this has been done we bonded everything and drove a ground rod at the array.
    See replies in red

  8. #8
    Solar Fanatic
    Join Date
    Feb 2010
    Posts
    11,542

    Default

    Rich I agree with you, but the inspector sees it differently. It suks I know, but they win every time. Well most of the time anyway. Unless you have a PE doing the design and stamped drawings, you do not have much to bargain with.

    To be honest if I were the PE doing it and the inspector dinged me, it is easier and less expensive on a project this size to just make the changes, than to fight it. Most review boards are the inspectors peers and will be biased. Now if this was say in Chicago, Boston, or Manhattan you could send union reps to the guys house and lean on him and his family to change his mind.
    MSEE, PE

  9. #9
    Administrator
    Join Date
    Feb 2011
    Location
    Annapolis Md
    Posts
    6,134

    Default

    The main problem is the code is so convoluted in the wy it is written there are rules in one section and exceptions to those in another.
    We already made the changes so water under the bridge on this one. I'm thinking of the future.

Posting Permissions

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