690.7 and single family homes

I just went to do a site visit today where the salesman sold this homeowner a 60-panel 18kw system. How does/is this allowed under 690.7? I have not looked at the single line to see how it's wired but I fail to see how this can be accepted by the AHJ. The service is a 200A and does have room for 40A of solar and will satisfy 705.12
:?:?
 

jaggedben

Senior Member
I don't see what 690.7 has to do with system size (other than how it might affect the economics).

A 200A service panel with 200A main breaker would not accommodate a 18kW system. But they could possibly go around that with a suppy-side connection, or by downsizing the main breaker, if certain conditions are met.

I'll grant that 18kW is on the huge side for a single family home (of the non 'compound' type, anyway). Seems like maybe the homeowner should look at some energy efficiency and not just solar. On the other hand, I just came back from my first visit ever to visit to South Carolina, and I can see how people there might be addicted to lots of air-conditioning.
 
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I don't see what 690.7 has to do with system size (other than how it might affect the economics).

You are right that a 200A service panel with 200A main breaker would not accommodate a 18kW system. But they could possibly go around that with a suppy-side connection, or by downsizing the main breaker, if certain conditions are met.

I'll grant that 18kW is on the huge side for a single family home (of the non 'compound' type, anyway). Seems like maybe the homeowner should look at some energy efficiency and not just solar. On the other hand, I just came back from my first visit ever to visit to South Carolina, and I can see how people there might be addicted to lots of air-conditioning.
Thanks for the response!

I am just looking at 600v as the maximum voltage in a single-family home is my concern here. It doesn't take to many series connections to hit 600v, unless your combing two strings to up the amperage and end up with close to 600+/- v and 22A on one breaker.
 

jaggedben

Senior Member
Thanks for the response!

I am just looking at 600v as the maximum voltage in a single-family home is my concern here. It doesn't take to many series connections to hit 600v, unless your combing two strings to up the amperage and end up with close to 600+/- v and 22A on one breaker.
Yes, well, the design will probably need two inverters. If using optimizers, then strings can be longer. It is certainly a lot more wiring to work at 600V instead of 1000V but that's going to be the nature of the job in this case.
 

electrofelon

Senior Member
Last I checked, fronius inverters are the only "residential" inverters that do 1kv. Assuming you use two inverters, you will have 4-6 total mppt's anyway which you will probably want to utilize so I dont see a 600v limit really effecting much.
 

ggunn

PE (Electrical), NABCEP certified
Thanks for the response!

I am just looking at 600v as the maximum voltage in a single-family home is my concern here. It doesn't take to many series connections to hit 600v, unless your combing two strings to up the amperage and end up with close to 600+/- v and 22A on one breaker.
What is your role in this? You apparently are unfamiliar with PV systems design.

It is definitely possible to interconnect 18kW of PV to a 200A service in compliance with the NEC, and the 600DCV limit on single family rooftops is irrelevant. Whether it is a good idea from the customer's POV or not is another question entirely.
 
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