1 It could be "on" a 10 or 25 kVA xfmr. The service is not the transformer.
2 You mean to say that a 50kVA unit would be more likely to be used for a 400A service than to be used for a 200A service. Again, the service is the not the transformer.
3 so you'd probably get at least a 600A service. And then the POCO would likely use a transformer bigger than 50 kVA, so you wouldn't have that problem.
4 BTW, am I correct in thinking that POCO transformer ratings are continuous ratings? If so, that's a factor of 80% (which is 1 / 125%) right there, the NEC rating of the service would be on a non-continuous basis. So the POCO transformer would likely never be more than 80% of the service size.
1 Sure, but the service is provided by the xfmr, the same xfmr the PV goes thru, so the size of it has to be taken into account at some point- why not at the first point?
If a customer says "hey, I want some PV", you don't run out and buy inverters without asking "what voltage service do you have?"
And after that "how many amps is your main switch" seems like a logical follow up.
But the amps of the main switch doesn't always equal the amps of the service, so next I'd ask "what size is the xfmr", the customer wouldn't know, so I'd ask the POCO- don't want to oversize the PV inverter output.
2 I'm trying to say a 50kVA xfmr wouldn't ever be supplying a 200A service, because it would be oversized 2x, and the POCO doesn't do that.
3 Yep. If it was a 600A irrigation load that ran for a month a year for a few hours a day, the 50kVA would work for 600A.
If it was 600A of heaters running 50% of the time, 75kVA would be the one. That's why I'm saying 75kVA would Be "standard" for someone using 600A on a regular basis.
I think the limit for single phase is 1200A / 150kVA in fact.
4 Doesn't the NEC end at the service point? So it's not factoring in the service xfmr at all?
:rant:
OF course it has. But its the utility's call as to "how hot" they will run the transformer and what they will charge so I still dont see what good it does you to conjecture/obsess about it
until you get the proposal from them. IF you are somewhat flexible with the system size, you could inquire what the max size PV without a transformer upgrade would be and weigh out the cost difference, customer needs, etc.
systems that are relatively large compared to the service size are usually supply side connected. In his case,
taking that meter main out and throwing it in the river is probably where I would start
I think that is pretty typical, even a bit large actually. In my experience, I usually find an NEC load calc to result in about 2.5 times the actual load. System I have been working on the last few days is actually a near textbook example:
1000 amp 120/208 service (ampacity of service entrance conductors), 150 KVA transformer (~420 amps). Actual load hovers right around 115 KVA (~320 amps) during peak times, Peak demand from last two years is 156 KVA
Dude! All I'm saying is that:
If there's a 25 kVA xfmr, it will be loaded to 100% of capacity if:
There are 208.3A of 120V loads.
OR
There are 104.15A a 240V loads.
And that means a limit of 100A of input from 240V PV inverters.
---
They don't give me the proposal- I give it to them!
Yes! Throw it in the river, zman! Best advice yet!
Could you elaborate? Is that single phase or three ph 120/208V? And why is there a 1000A service when the load never gets close to 500A?