Help on inverter amps and electric panel allowance

[frasere2]

So, I have consulted several electricians and 2 solar vendors. The electricians say one thing, the vendors' electrical engineers say another. Here is the issue:
I just bought a 225buss/200amp panel with 70amp solar ready, (homedepot.com/p/Eaton-CH-200-Amp-42-Circuit-EUSERC-Solar-Power-Meter-Breaker-Outdoor-Surface-Mount-CMBE4242PV200BS/306673952#overlay), I have a proposed solar array that would need (2) 7.6kw inverters that have a max output of 64amps. The vendors say the 120% rule means that that max the electric panel can accept is 270amps from both the electric service and the solar, but there has to be a 125% buffer, so the max on the solar would be 56amps (56ax125%=70a). Here are the pages for the 2 vendors:

Grid-tied Solar and the Dreaded 120% Rule | altE Solar Blog

Once solar inverters get larger than 7680W, installers often will run into a NEC restriction known as the 120% rule. We go over some solutions...

www.altestore.com

All You Need To Know About The 120% Rule

CharacteristicsManufacturer: blog

www.renvu.com

Whereas 3 electricians have said that the panel can accept the 64 amps from the inverters (without degrading the main breaker).
Who is correct? I've literally been dealing with this for a week. Oh and the manufacturer of the panel also says it would be ok too with the 64 amps.

Thanks!

 

[hayhayday]

7.6kw inverters usualy take 40a(125% of 32a) breaker and 2*40a >70a your panel allows. Could you use 2x 6kw or 7.6 + 5kw instead?

 

[Hedges]

I believe it is 56A.
70A breaker x 80% max continuous load = 56A (for a thermal breaker)

If it was a magnetic hydraulic breaker (which I only know of in other mounting styles), it would be good for up to 100% continuous (maybe some 95%)

I think the 120% rule could have been a 200% rule, without overloading L1/L2 busbar, so long as installed at the far end.
However, neutral can carry up to the 120% (or 200%) if you have that much imbalance.

Will the two inverters have panel orientations giving max output at the same time? Or different, so reduced peak current?
If that doesn't fix the issue, configure them for reduced output current (12.5% lower). Same PV panels just means a bit overpaneled.

What I'm doing for same 2x inverter size is a 200A main breaker followed by Polaris lugs, so not limited by 120% rule of busbar.

 

[frasere2]

I believe it is 56A.
70A breaker x 80% max continuous load = 56A (for a thermal breaker)

If it was a magnetic hydraulic breaker (which I only know of in other mounting styles), it would be good for up to 100% continuous (maybe some 95%)

I think the 120% rule could have been a 200% rule, without overloading L1/L2 busbar, so long as installed at the far end.
However, neutral can carry up to the 120% (or 200%) if you have that much imbalance.

Will the two inverters have panel orientations giving max output at the same time? Or different, so reduced peak current?
If that doesn't fix the issue, configure them for reduced output current (12.5% lower). Same PV panels just means a bit overpaneled.

What I'm doing for same 2x inverter size is a 200A main breaker followed by Polaris lugs, so not limited by 120% rule of busbar.

Okay, I am not familiar with polaris lugs, how does this circumvent the 120% rule of busbar? I'm just trying to make sure it passes permitting. I of course can derate the main electric panel to 175a, but I'd rather not, especially if I'm adding an electric car and heat pump later. So my choices are:
1) Reduce the solar array to use only a 11.4kw inverter, but this won't cover 100% of electric needs once I add the electric car and heat pump later
2) Derate the main breaker to 175amps (same issue as above)
3) Do a line side tap, which takes approval from electric company and city
4) Use polaris lugs??? somehow to avoid the 120% rule (this would be great if it works for the local permitting office.) How is this setup and where do I get info on it?

 

[Hedges]

If you feed grid and PV into breaker panel busbar, you're supposed to limit the sum to 120% of busbar rating, and put PV at opposite end.

If you had just 200A main breaker (and service disconnect) coming from grid (no branch circuits in that box),
80A or whatever coming from PV (you could use 200A or 225A busbar with 150A main breaker and also have loads on that panel, or a 100A or larger panel called "PV aggregator" so 120% doesn't apply.)
200A main breaker on a panel with branch circuits.

Now, 280A only exists on cables between those several main breakers. Or not even on the cables (given just 3 panels connected to it.)
"Polaris" is a screw terminal connector available for 2 to 5 wires. It can be rated 400A or so, so even two 200A feeds into it aren't a problem. Every wire off it is protected by main breaker on its respective panel.

Manufacturer of Aluminum and Copper set screw connectors for the Utility, OEM, and Contractor and Industrial Markets

Square D QO 200 Amp 2-Pole Outdoor Circuit Breaker Enclosure with QOM2200VH Breaker QOM2E2200NRB - The Home Depot

The Square D by Schneider Electric QO 200 Amp Outdoor Circuit Breaker Enclosure includes a two-pole QOM2 frame sizes circuit breakers 100-225 amp capacity for use as an exterior disconnect. This breaker

www.homedepot.com

I'm planning to use this one. Will connect a 100A fused disconnect for PV, 200A main breaker panel, 125A main breaker panel to eventually be backed up loads. Interlocked "generator" breakers on each of those panels will make it possible to battery back up one or both. Will have load-shed relay so they can be disconnected depending on SoC. As compared to doing this with a breaker panel that is also service entrance, this will still have grid input to inverter.

"Line side tap" likely has limit on allowed current, maybe 40A breaker.
My putting a 200A service disconnect before 200A breaker panel accomplishes same thing.
My existing house happened to have this so I've done it here already.

 

[Mike 134]

Why do you feel if you derate the main breaker to 175 amps you won't have enough power? Yet you'd have enough at 200?

You said you bought a "solar ready" 200A panel. What size panel are you replacing?

 

[Danke]

3) Do a line side tap, which takes approval from electric company and city
4) Use polaris lugs??? somehow to avoid the 120% rule (this would be great if it works for the local permitting office.) How is this setup and where do I get info on it?

I would imagine you need approval whatever you do if you’re back feeding the grid.

 

[Hedges]

Now, 280A only exists on cables between those several main breakers. Or not even on the cables (given just 3 panels connected to it.)
"Polaris" is a screw terminal connector available for 2 to 5 wires. It can be rated 400A or so, so even two 200A feeds into it aren't a problem. Every wire off it is protected by main breaker on its respective panel.

While all L1 & L2 busbars and wires are limited to 200A by this scheme, and neutral in each breaker panel is limited to 200A, it is possible for you to consume a total of 280A from L1 between two breaker panels (if you have two breaker panels, which you don't but I plan to.) Which means N conductor from utility transformer through meter box and neutral wire will carry 280A. Which it is not designed to do.

I don't think NEC and the committee which wrote it, or PG&E or your AHJ, is clever enough to have figured this out yet.
For anyone who installs 2 or more breaker panels and gets around 120% rule this way, consider limiting the total of single-phase circuits on any one phase to 100%. That way, if the overload happens anywhere, it will be on utility distribution line not your drop or wires.

I would imagine you need approval whatever you do if you’re back feeding the grid.

Yes, but the question is how to best support 80A PV breaker and 200A main breaker. Get the design compliant before requesting approval.
400A panel would be an option, but expensive.
I suggested two, 200A panels (about $200 each)

 

[frasere2]

Why do you feel if you derate the main breaker to 175 amps you won't have enough power? Yet you'd have enough at 200?

You said you bought a "solar ready" 200A panel. What size panel are you replacing?

So I actually have a 200/200 electric panel, I bought a 225/200 electric panel so I could have the 70amps for the solar without having to derate the main breaker. The manufacturer said this would be fine for 64a from the inverters. However, it seems that is incorrect (75% sure now). So my choices are:
1) Keep the current 200/200 Elec panel, derate main breaker to 150a, then use 80a breaker for inverters are 64 amps
2) Install new elec panel 225/200a, derate main breaker to 175a, then use 80a breaker for inverters are 64 amps
3) Install new elec panel 225/200a, don't derate main breaker and hope the manufacturer and 2 of 3 of the electricians I consulted were right.
4) Drop the entire solar array in size so I only use (1) 11.4kw inverter at 54amps, and either derate existing elec panel to 175a breaker, or install new 225/200 elec panel

This really shouldn't be this complicated. There about 5 things in solar installation that just mushy when it comes to installation and requirements (eg. fire setbacks, roof attachments, panel orientation, # of panels, etc.). One could make killing if they could standardize and streamline this process.

 

[Danke]

So I actually have a 200/200 electric panel, I bought a 225/200 electric panel so I could have the 70amps for the solar without having to derate the main breaker. The manufacturer said this would be fine for 64a from the inverters. However, it seems that is incorrect (75% sure now). So my choices are:
1) Keep the current 200/200 Elec panel, derate main breaker to 150a, then use 80a breaker for inverters are 64 amps
2) Install new elec panel 225/200a, derate main breaker to 175a, then use 80a breaker for inverters are 64 amps
3) Install new elec panel 225/200a, don't derate main breaker and hope the manufacturer and 2 of 3 of the electricians I consulted were right.
4) Drop the entire solar array in size so I only use (1) 11.4kw inverter at 54amps, and either derate existing elec panel to 175a breaker, or install new 225/200 elec panel

This really shouldn't be this complicated. There about 5 things in solar installation that just mushy when it comes to installation and requirements (eg. fire setbacks, roof attachments, panel orientation, # of panels, etc.). One could make killing if they could standardize and streamline this process.

No go on line side tap?

 

[Hedges]

PG&E document on line-side tap here.
No mention of an amperage limit.
It may have been an adapter inserted under the meter that had 40A (or was that 20A?) limit.
You can buy fancy electrical boxes with this built in (I think they cost a bit more than Polaris connectors; maybe 50x ~ 100x as much?

https://www.pge.com/includes/docs/pdfs/shared/customerservice/nonpgeutility/electrictransmission/handbook/TD-6999B-048.pdf

https://code-authorities.ul.com/wp-content/uploads/sites/4/2016/12/UL__LineSideBreaker.pdf

QOWC60M200PFY - Energy center, QO, 1 phase, 61 available circuits, 200A, PoN, ringed socket, semiflush, UG, solar, battery, gen ready | Schneider Electric USA

Schneider Electric USA. QOWC60M200PFY - Energy center, QO, 1 phase, 61 available circuits, 200A, PoN, ringed socket, semiflush, UG, solar, battery, gen ready.

www.se.com

(It is possible you get some other features besides a line-side tap built in. You'd better, for the price of 2x 7.7kW inverters!)