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Thread: 240 delta with high leg solar installation

  1. #21
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    Quote Originally Posted by Smart $ View Post
    Did you solidly ground the wye point on the 480Y/277 side?

    The utility side is 240 delta high leg with a grounded-neutral center tap? (The service; not the transition transformer)


    If yes to both,
    the inspector needs his head examined (more appropriately, his credentials revoked).
    If no to either or both, the inspector may have a point.


    Playing Devils advocate, does the same logic apply in reverse? if you make an error should your credentials be revoked? I am all ways amazed how people think. If the person at the inspection can not explain his or her own work, why is the inspector wrong?

  2. #22
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    wouldn't 450.6C and 250.30 apply to the transformer install?

    I'm not saying the OCPD in the service panel will not function to shut down in a ground fault,,,,BUT,,,,, doesn't the grounding and bonding requirement still apply? (I haven't seen an Exception to it, in the code)

    edit to add, 2014 NEC used.

  3. #23
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    Quote Originally Posted by acrwc10 View Post
    wouldn't 450.6C and 250.30 apply to the transformer install?
    250.30 would. I don't think 450.6 is relevant. There's only one transformer here. 705 and 690 govern the installation of the inverter.

    I'm not saying the OCPD in the service panel will not function to shut down in a ground fault,,,,BUT,,,,, doesn't the grounding and bonding requirement still apply? (I haven't seen an Exception to it, in the code)

    edit to add, 2014 NEC used.
    From the OP's descriptions the system is grounded and bonded adequately, at least in regards to the general concepts (i.e. inverter-side neutral is grounded), leaving aside details of conductor sizing and installation, etc. It might be that what's he's calling the 'GEC', that bonds to the neutral secondary to the service ground bar, should be called a 'Bonding Jumper' instead. Physically, it would serve the same purpose. Perhaps the inspector's objection is just a quibble over the naming and number of green wires, but it doesn't seem so.

  4. #24
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    Quote Originally Posted by acrwc10 View Post
    Playing Devils advocate, does the same logic apply in reverse? if you make an error should your credentials be revoked? I am all ways amazed how people think. If the person at the inspection can not explain his or her own work, why is the inspector wrong?
    If I make an error on such a basic issue, one that should be an obvious prerequisite for said credentials, and I am still adamant on my position after it is pointed out, along with several other indicators that I'm wrong (e.g. stamped, plan-checked drawings)... heck yeah!
    I will have achieved my life's goal if I die with a smile on my face.

  5. #25
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    once again playing Devil's advocate, Art 250 lays out the requirements for when the transformer/separately derived system requires "grounding". The input/primary side is the PV, that side is grounded, the OP says its a 480/277Y. The secondary is a 240 Delta (not grounded, no neutral) connected to a 240v 4wire system. where in the code does it say you can solidly connect an ungrounded to a grounded system? The output characteristics of the two systems don't match. I'm not saying they won't work, I'm just saying "per the letter of the code" it seems to be a violation. The system is grounded or ungrounded. Maybe a code change to address it?

  6. #26
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    A high-leg delta is not an ungrounded system. That doesn't change because the grounded conductor is not brought to one side of a transformer, it's still a grounded system. Also the two systems are not 'solidly connected'. If the engineer says that the setup is ok and especially if Solaredge agrees then it should be fine.

    The code is permissive, if it doesn't address something that doesn't mean you can't do it. Where in the code does it say you cannot power a delta with a wye, or vice versa? What code section are you thinking that it violates?
    Last edited by jaggedben; 05-16-17 at 01:27 PM.

  7. #27
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    Quote Originally Posted by acrwc10 View Post
    ...where in the code does it say you can solidly connect an ungrounded to a grounded system?
    If the connection is through a transformer, it is not a solid connection.

  8. #28
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    Quote Originally Posted by ggunn View Post
    If the connection is through a transformer, it is not a solid connection.
    Connecting a secondary of one transformer to the primary of another is a solid connection. If the secondary of the source transformer is grounded, the entire secondary system is grounded, including the primary of the supplied transformer. In the OP's scenario, the inspector seems to be saying the primary of the downstream transformer (relative to the utility) is not grounded. That is quite simply not true.
    I will have achieved my life's goal if I die with a smile on my face.

  9. #29
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    Quote Originally Posted by Smart $ View Post
    Connecting a secondary of one transformer to the primary of another is a solid connection. If the secondary of the source transformer is grounded, the entire secondary system is grounded, including the primary of the supplied transformer. In the OP's scenario, the inspector seems to be saying the primary of the downstream transformer (relative to the utility) is not grounded. That is quite simply not true.
    If the PV inverter is supplying 480/277 Y that is the primary side, of the transformer, the current is not flowing to the PV from the utility. The output of that same transformer is an "ungrounded" 240 Delta, this would by default be the "secondary" side of the transformer. Can we agree that is true?

    Now if that same "ungrounded" 240 Delta secondary is supplying/tied to the "Grounded" 240 Y system. That makes it a violation, your transformer output is required to be grounded.

  10. #30
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    Quote Originally Posted by acrwc10 View Post
    If the PV inverter is supplying 480/277 Y that is the primary side, of the transformer, the current is not flowing to the PV from the utility. The output of that same transformer is an "ungrounded" 240 Delta, this would by default be the "secondary" side of the transformer. Can we agree that is true?
    No.

    Technically neither side is primary. You are [subjectively] correct in that more energy will be transferred from the 480V side to the 240V side. However, without utility voltage there would be no transfer. Now consider a typical transformer with no load. Both sides have voltage but only one side has potential without the other and that is the side that is considered the primary.


    Now if that same "ungrounded" 240 Delta secondary is supplying/tied to the "Grounded" 240 [DELTA] system. That makes it a violation, your transformer output is required to be grounded.
    [FIFY]

    You are talking about a separately derived system. This is not a separately derived system. This is two interconnected electric power production sources... and one is a utility source. Additionally, this interconnected system is grounded. It just happens to be grounded somewhere other than at the 240V:480/277V transformer of discussion.
    I will have achieved my life's goal if I die with a smile on my face.

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