Existing #6 and 40 amp breaker good for 18kpv tie in?

[bfaubion]

After doing a lot of investigation, I decided to forgo a whole house 200 amp backup scenario with the 18kpv. What I do have is a partial home backup option, tying the inverter into a breaker in the house subpanel.

I’ve essentially got a non-used 40 amp breaker, with either stranded copper #8 or #6 that went into a smaller subpanel that housed breakers for an old wine cooler I tore out. So the little subpanel box sits there empty, with 2 #8 (or #6) lines and a ground coming in, at place where I could easily add the 18kpv… unless I will be severely limited by a 40 or 50 amp breaker (if it’s #6). I’ve also got a double pole 40 that goes to a 240 socket in the garage

Planning on 3200 to 4000 watts of solar, and maybe a single EG4 LL rack battery, or possibly the PowerPro. Average about 10 kWh per day when not using HVAC. I feel like the 18kpv is overkill for me, but it handles the grid tie and hybrid features great, and I could always require it in the future to whole home backup.

So I’m wondering, is wiring the 18kpv to a 40 or 50 amp breaker severely limiting? And is that an issue if my bus bar is 200 amps? (The sticker on the subpanel was removed, cannot tell if it’s 200 or 225, assuming 200 for now).

 

[Hedges]

40A at 240V is ~10kW.
But only run 80% continuous, so 32A, 8kW draw or backfeed.

If it will be backfeeding, use or relocate to end of busbar.
120% rule: 200A busbar x 120% = 240A, 240A - 200A main (or feed) = 40A backfed PV breaker allowed.

Your 18kPV can supply more than 32A. Just configure it to limit current on its grid connection to 32A max.

That's plenty for reasonable loads. The inverter can supply more from battery.
More than enough for 4000W PV backfeed.

 

[bfaubion]

Welp that makes it easy! haha, no new wire runs needed then for a 40 amp breaker, since that’s all it can likely take. breakers are from the late 80’s.. would it be a good move to go ahead and get a new 40 amp double pole breaker considering it’s going to backfeed?

My only issue then is that the top breaker lines needs to be swapped out with the bottom breaker lines if I’m going to use that for solar, and I’m not sure I have enough wire length there in the box. If I can’t swap it out because it doesn’t reach the bottom of the bus bar, then that means I’d need to use the other 240 line, but that goes to my 240 plug.

Any issues with just dumping the existing 240 plug in the garage and converting that to a disconnect?

 

[Hedges]

I think breakers age with hours of operation at high current.
I've had some trip below rating.
But if it has had an easy life, may not be a problem.

You could test it!
Got 3x 15A space heaters? hook them up to run off one leg, see if it holds a very long time.

I made a breaker tester with a transformer to boost current. Couple space heaters and it made 86A, tripped a 40A "new out of box" breaker I got on eBay.

You could extend the wire.

I would consider fudging the "far end of busbar" rule, so long as there weren't more than 200A of breakers beyond the backfed one.

If you get rid of the 240V outlet in garage, how will you charge your Tesla?

 

[bfaubion]

OK, well I’ll hire an electrician just to take a look along with something else if I’m feeling like it’s uncertain.. no Tesla for me sir.. perhaps a Chevy Bolt at some point. Although I do like the plug-in hybrids.