How does everyone here handle their PV transformer disputes with AHJ's or are we the only one having issues? It seems at least half the time we have a transformer in a design we get an inspector that wants to have an opinion about it. Usually saying we are conflicting ourselves with our specifications of the primary winding towards the utility. I feel like the NEC doesn't spend enough time clearly depicting how to design a transformer into a PV system and it creates problems like this because those who do not have a more in depth knowledge of transformer anatomy and the reasoning behind design considerations do not understand why engineer's make certain decisions regarding system design.
The latest issue was that the AHJ wanted us to remove our neutral bond on the PV side of the (480Y-208Y) transformer (within the first disconnecting means and move it to to the utility side of the transformer because "...that is the secondary of the transformer..." I told him that made no sense and that we'd then have a floating neutral on one side and a neutral bonded in two places on the other side and explained the problems that created. He responded that hes not an engineer so he doesn't have to understand that level of detail and the code book doesn't require an engineer to be able to follow it. If that were the case then why bother getting an engineers stamp on drawings instead just have an NEC compliant guaranteed stamp that electricians can carry around and say they followed the code? To clarify, that is by no means a knock on electricians, its more a reference that the electrician's license requires a working knowledge of the NEC and secondarily its about the fact that we each have our own role in the equation, they keep us honest when we don't think about real life problems, and even when we make mistakes, and we work out the details that require our background.
That digression aside the solution of the inspector was to continue to keep a second bond on the utility side of the transformer but to bond the neutral at the first disconnect from the inverter. That makes no sense at all and isn't safe but I can't find anywhere in the NEC that tells him that is wrong, just engineering knowledge of the system, which he negates, and other code references such as IEEE, which he also negates because that is an "engineer's code and hes not an engineer" which again, seems quite unjustified; how would you handle this, or is there a reference I am missing with bonding that says something clear enough in this situation (I've already tried the argument that design should consider looking at primary in both directions when choosing OCPD, but he again didn't understand that, says it only applies to OCPD - which isn't wrong but hes missing that its the point of inferring that a transformer isn't straight forward, and he says in that case it shouldn't be bonded on either side then
. The neutrals are not physically connected so we have to call it separately derived whether he likes it or not, the problem is he is saying that the PV is the generation source so it is 'deriving' the neutral on the secondary side of the transformer which is the utility side without considering that the PV is actually a delta generator with a neutral reference (and the capability of reactive power support which can balance power to a neutral now on smart-grid inverters); PV is also not a voltage source but a current source but the voltage source (which distinguishes the potential difference between conductors) is in fact the utility.
This is more than a specific problem I am looking to resolve, more looking to compile an arsenal of info regarding thoughts on PV transformers, and the problems you face with confusion, the solutions you came up with - more of a lessons learned post and see if there are enough repeated issues out there that we should write a letter to the CMP for Art 690 for clarification in 2023.
What other problems do you folks face with PV transformer confusion? How do you handle them?
The latest issue was that the AHJ wanted us to remove our neutral bond on the PV side of the (480Y-208Y) transformer (within the first disconnecting means and move it to to the utility side of the transformer because "...that is the secondary of the transformer..." I told him that made no sense and that we'd then have a floating neutral on one side and a neutral bonded in two places on the other side and explained the problems that created. He responded that hes not an engineer so he doesn't have to understand that level of detail and the code book doesn't require an engineer to be able to follow it. If that were the case then why bother getting an engineers stamp on drawings instead just have an NEC compliant guaranteed stamp that electricians can carry around and say they followed the code? To clarify, that is by no means a knock on electricians, its more a reference that the electrician's license requires a working knowledge of the NEC and secondarily its about the fact that we each have our own role in the equation, they keep us honest when we don't think about real life problems, and even when we make mistakes, and we work out the details that require our background.
That digression aside the solution of the inspector was to continue to keep a second bond on the utility side of the transformer but to bond the neutral at the first disconnect from the inverter. That makes no sense at all and isn't safe but I can't find anywhere in the NEC that tells him that is wrong, just engineering knowledge of the system, which he negates, and other code references such as IEEE, which he also negates because that is an "engineer's code and hes not an engineer" which again, seems quite unjustified; how would you handle this, or is there a reference I am missing with bonding that says something clear enough in this situation (I've already tried the argument that design should consider looking at primary in both directions when choosing OCPD, but he again didn't understand that, says it only applies to OCPD - which isn't wrong but hes missing that its the point of inferring that a transformer isn't straight forward, and he says in that case it shouldn't be bonded on either side then
. The neutrals are not physically connected so we have to call it separately derived whether he likes it or not, the problem is he is saying that the PV is the generation source so it is 'deriving' the neutral on the secondary side of the transformer which is the utility side without considering that the PV is actually a delta generator with a neutral reference (and the capability of reactive power support which can balance power to a neutral now on smart-grid inverters); PV is also not a voltage source but a current source but the voltage source (which distinguishes the potential difference between conductors) is in fact the utility.This is more than a specific problem I am looking to resolve, more looking to compile an arsenal of info regarding thoughts on PV transformers, and the problems you face with confusion, the solutions you came up with - more of a lessons learned post and see if there are enough repeated issues out there that we should write a letter to the CMP for Art 690 for clarification in 2023.
What other problems do you folks face with PV transformer confusion? How do you handle them?
