That is clear under 2023/2026 NEC 705.30(F). But 2020 NEC 690.9(D) sometimes required considering it primary for compliance with 450.3. So when discussing 690.9(D), it is more clear to stick with inverter side and utility side.The inverter side of a 480/277V wye to 208V delta interconnection transformer is the secondary.
It was safe to remove this since there are other NEC sections that require conductors and equipment in the backfeed path be sized to the PV system. That would include the transformer. The requirement in the exception in 690.9(D) was more of a reminder. To remind AHJs that the transformer does not require protection from a current limited source as long as the rating is equal to or greater than the source rating. These types of reminders were more common in the code in the past when objections by AJHs less familiar with PV came up more often.2020 NEC 690.9(D) Exception says you don't have to do that if the sum of the ratings of the inverters does not exceed the transformer rating (only reasonable way to read it for multiple inverters). Now 2023/2026 NEC 705.30(F) says you never have to do that. So it's less restrictive.
OK, but under the 2023 NEC that has now changed to the transformer never needing protection from the source with the lower fault current, regardless of the transformer rating compared to the source rating. So it seems the historical progression has been "some AHJs are being overly conservative with transfomers and PV" to "690.9(D) is there to inform them when that is necessary" to "actually, it's never necessary per 705.30(F)."The requirement in the exception in 690.9(D) was more of a reminder. To remind AHJs that the transformer does not require protection from a current limited source as long as the rating is equal to or greater than the source rating.
The convention used by all the AHJs I have dealt with since I designed the first system where I had to step down from 480V to 208V has always been the the side of the transformer connected to the utility is the primary side.That is clear under 2023/2026 NEC 705.30(F). But 2020 NEC 690.9(D) sometimes required considering it primary for compliance with 450.3. So when discussing 690.9(D), it is more clear to stick with inverter side and utility side.
Yes.Also, to step back for a minute, more on this notion of "current limited source." Safety-wise, does an inverter really behave at least as well as if it had an OCPD installed on its AC output, with setting equal to its maximum rated continuous current?
To remind AHJs that the transformer does not require protection from a current limited source as long as the rating is equal to or greater than the source rating. These types of reminders were more common in the code in the past when objections by AJHs less familiar with PV came up more often.
That's great for pre 690.9(D), or post 705.30(F). But for the 2020 NEC and earlier versions with 690.9(D), if the arrangement didn't qualify for the exception, then also considering the inverter side as primary and complying with 450.3 from that point of view was required (for better or worse).The convention used by all the AHJs I have dealt with since I designed the first system where I had to step down from 480V to 208V has always been the the side of the transformer connected to the utility is the primary side.
Great. So if we accept that, now to omit OCPD at the inverter when it and the transformer are outside, and 240.21(C)(1) does not apply, you just need to get 240.21(C)(4) changed to permit secondary conductors to terminate on a current limited source, rather than on "a single circuit breaker or a single set of fuses". Since as you say there is no additional hazard. Or maybe it would be better added to 705.30(F).Yes.
I will continue to use 690.9(D) until it is no longer there or until an AHJ rules against me. I have invoked it several times in more than one jurisdiction and it has never been challenged.Great. So if we accept that, now to omit OCPD at the inverter when it and the transformer are outside, and 240.21(C)(1) does not apply, you just need to get 240.21(C)(4) changed to permit secondary conductors to terminate on a current limited source, rather than on "a single circuit breaker or a single set of fuses". Since as you say there is no additional hazard. Or maybe it would be better added to 705.30(F).
Cheers, Wayne
690.9(D) does not reference 240.21(C) and in no way provides any relief from its requirements. The topic of 690.9(D) is "overcurrent protection for a transformer" not "overcurrent protection for conductors."I will continue to use 690.9(D) until it is no longer there or until an AHJ rules against me. I have invoked it several times in more than one jurisdiction and it has never been challenged.
690.9(D) says "Overcurrent protection for a transformer..." Overcurrent protection for conductors is covered by 690.9(A)(1). I am sorry you do not agree, but I have tested this with several AHJs, and in every case they approved my design.690.9(D) does not reference 240.21(C) and in no way provides any relief from its requirements. The topic of 690.9(D) is "overcurrent protection for a transformer" not "overcurrent protection for conductors."
That's a 2020 NEC reference, and these transformer secondary conductors connected to the inverter AC outputs fall under 2020 NEC 690.9(A)(2), which says:Overcurrent protection for conductors is covered by 690.9(A)(1).
