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Thread: 240 delta with high leg solar installation

  1. #1
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    240 delta with high leg solar installation

    Need Help! I have an installation were the main service is a 240 delta with a high leg. We are using a SolarEdge 33k 480v inverter. We have installed a 240 delta to 480/277y transformer in between. Everything was stamped by engineer and passed city plan check, but now the city inspector is saying it won't pass because if there was a fault to ground on the primary side of the transformer it would not trip the breaker. Please advise, I am looking for a solution that would not cause us to have to use 3 single phase SolarEdge inverters and have to change out all of the p700 optimizers we currently have onsite. There are 90 Canadian Solar 315watt panels. Thank you in advance for your help

  2. #2
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    Quote Originally Posted by BenJChaney View Post
    Need Help! I have an installation were the main service is a 240 delta with a high leg. We are using a SolarEdge 33k 480v inverter. We have installed a 240 delta to 480/277y transformer in between. Everything was stamped by engineer and passed city plan check, but now the city inspector is saying it won't pass because if there was a fault to ground on the primary side of the transformer it would not trip the breaker. Please advise, I am looking for a solution that would not cause us to have to use 3 single phase SolarEdge inverters and have to change out all of the p700 optimizers we currently have onsite. There are 90 Canadian Solar 315watt panels. Thank you in advance for your help
    I think the city inspector needs to find a new job. Which side of the transformer is he referring to?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  3. #3
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    Quote Originally Posted by BenJChaney View Post
    if there was a fault to ground on the primary side of the transformer it would not trip the breaker.
    Primary is an ambiguous term in this application, because power and energization come from both directions. Does primary mean the 480V side or the 240V side?

  4. #4
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    Quote Originally Posted by BenJChaney View Post
    Need Help! I have an installation were the main service is a 240 delta with a high leg. We are using a SolarEdge 33k 480v inverter. We have installed a 240 delta to 480/277y transformer in between. Everything was stamped by engineer and passed city plan check, but now the city inspector is saying it won't pass because if there was a fault to ground on the primary side of the transformer it would not trip the breaker. Please advise, I am looking for a solution that would not cause us to have to use 3 single phase SolarEdge inverters and have to change out all of the p700 optimizers we currently have onsite. There are 90 Canadian Solar 315watt panels. Thank you in advance for your help
    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.
    I will have achieved my life's goal if I die with a smile on my face.

  5. #5
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    Yes to both Smart$. Sorry I am a bit out of my league when it comes to dealing with a high leg. What would be a good way to prove to the inspector that it would trip in the case of a fault to ground?

  6. #6
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    If a fault to ground occurs on any of the ungrounded primary wires (call them A, B and C), then the fault current will flow through the fault to ground and and from that ground/EGC connection back to the grounded neutral (middle of the A-C POCO secondary winding). The excess current in A, B, C or more than one, depending on the fault, will trip the service OCPD, typically a three pole breaker.

    If a fault occurs on the secondary side of your delta-wye transformer, fault current will flow through that fault to grounded metal which is both connected to the GEC and the solidly grounded wye point of the secondary. It will probably trip the breaker on the primary side of the transformer as a result.
    If the fault is past the secondary side protection on your transformer, it will most likely trip that OCPD and possibly the primary side OCPD too.

    If there is a fault between any secondary ungrounded conductor and any primary ungrounded conductor, fault current will flow in both sets of windings and through the common (metallically connected) wye point of your secondary winding and the POCO secondary (your service). Either your secondary OCPD or your primary ODPC or the service OCPD would then open.

  7. #7
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    Quote Originally Posted by BenJChaney View Post
    Yes to both Smart$. Sorry I am a bit out of my league when it comes to dealing with a high leg. ...
    The fact that it is a high-leg is essentially irrelevant.

    The inspector's objection, as you've described it, makes no sense whatsoever. If sharing Golddigger's explanation doesn't work, then perhaps the best way to change his mind is to try to get him to explain in minute detail how a ground current wouldn't trip the breaker. Or go back to the plan checkers who approved it and get them to intervene. Or utilize your engineer if you're not good at discussing the theoretical stuff yourself.

  8. #8
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    Thank you everyone for your response. Thats what im going to do, get the engineer involved and let them hash it out. I intially lost confidence that it was installed correctly, but after seing your responses I believe we have a leg to stand on. Thanks again

  9. #9
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    Quote Originally Posted by BenJChaney View Post
    ... I believe we have a high leg to stand on. ...
    FIFY
    I will have achieved my life's goal if I die with a smile on my face.

  10. #10
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    I guess after talking to the Inspector more I need to make a correction to my post. On the service side of the xfmr, there is no neutral connection. There is one on the inverter side, but not service side. The GEC is tied continuously from the array, through the inverter, through the disconnect,through the xfmr which is also tied to the neutral on the inverter side of xfmr, through the disconnect, and tied the the ground/neutral bar at the service. I'm including a photo of the label on the transformer. I just cannot wrap my head around what he is saying, but iI am inexperienced when it comes to this and fully ready to admit I'm wrong. I just wanna make sure the install is correct and safe.
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