Solar ready electrical panel max amps allowed?

[fraser]

So I bought a new electric panel that is solar ready to allow for higher amps from the about to be installed solar system. The panel is an Eaton CH 200 Amp 42-Circuit EUSERC Solar Power Meter Breaker Outdoor Surface Mount (225Bus,200amp breaker), that says it allows 70amp solar backfeed. Soooo, when I spoke with the solar vendor, they said the 70 amps had to be reduced by the 120% rule which would only allow about a 13.4kw inverter. Since the 2 inverters would be 2 7.6KW inverters and would max out at 64 amps, this would not work. Supposedly their senior engineer confirmed this. So, I called Eaton tech support, who confirmed with a supervisor, that the full 70 amps could be used and the 64 amps from my 2 inverters would be fine. Makes sense as how do they advertise it as a 70amp solar ready panel? So, who is right? And why is that not just written plainly somewhere ????

[Mike 134]

The panel maker's Electrical engineer is correct, and the solar salesman is wrong. (Why am I not surprised) 2020 NEC article 690.94b(2) states your connections cannot exceed 120% of the bussbar rating. 225 x 1.20 = 270

[fraser]

The panel maker's Electrical engineer is correct, and the solar salesman is wrong. (Why am I not surprised) 2020 NEC article 690.94b(2) states your connections cannot exceed 120% of the bussbar rating. 225 x 1.20 = 270

So 64 amps can be backfed from the inverters no problem (2 7.6w growatt inverters)? Why on earth would the solar vendor even bring up the 120 rule regarding the 70 amps then? I have no idea. I tried to get PG&E to decide this and they want me to submit the entire application first. Can't confirm or deny. 3 hours wasted on this just today. I've asked an electrician, but he said he needed to get back to me.

[bcroe]

If your PoCo feed is at one end of the bus bar, and your inverter
breakers at the opposite end, it is physically impossible to
overload the bus bar. But with your solar ready panel, you
should be good, with belt and suspenders. Just how you convince
the locals I do not know, I think my installer never worried about
120% (but I did). good luck, Bruce Roe

[fraser]

If your PoCo feed is at one end of the bus bar, and your inverter
breakers at the opposite end, it is physically impossible to
overload the bus bar. But with your solar ready panel, you
should be good, with belt and suspenders. Just how you convince
the locals I do not know, I think my installer never worried about
120% (but I did). good luck, Bruce Roe

So here is what the vendor says, after consulting with a "senior engineer" at his company:

The Eaton catalog confirms the 270A max for source currents (main + solar), which allows a 70A solar backfeed breaker and the product catalog note is very carefully worded. A 70A breaker CANNOT protect 70A of continuous inverter output current. There must be a 1.25 safety factor REQUIRED by the NEC. A 70A breaker is only allowed to protect up to 56A of continuous current.

Am I crazy? He seems he is saying the 64amps would be too much.

[Mike 134]

So here is what the vendor says, after consulting with a "senior engineer" at his company:

The Eaton catalog confirms the 270A max for source currents (main + solar), which allows a 70A solar backfeed breaker and the product catalog note is very carefully worded. A 70A breaker CANNOT protect 70A of continuous inverter output current. There must be a 1.25 safety factor REQUIRED by the NEC. A 70A breaker is only allowed to protect up to 56A of continuous current.

Am I crazy? He seems he is saying the 64amps would be too much.

The Eaton engineer is once again correct. Any load lasting more than 3 hours is considered continuous, so you have to limit breakers and wiring to 80% 70a x .80 = 56. 125%, 56a x 1.25 = 70. So a 70A breaker if loaded more than 3 hours can only carry 56 amps. They do make 100% rated breakers for industrial and large commercial applications, but I've never seen them for a residential plug-in panel,

[fraser]

The Eaton engineer is once again correct. Any load lasting more than 3 hours is considered continuous, so you have to limit breakers and wiring to 80% 70a x .80 = 56. 125%, 56a x 1.25 = 70. So a 70A breaker if loaded more than 3 hours can only carry 56 amps. They do make 100% rated breakers for industrial and large commercial applications, but I've never seen them for a residential plug-in panel,

Okay, so I CANNOT use the inverters that have 64 amps then??? (That is what the vendor said, not the Eaton engineer). I swear the manufacturer shouldn't be able to advertise that it can take 70amps of solar if it really can only accept 56amps....

[Mike 134]

Okay, so I CANNOT use the inverters that have 64 amps then??? (That is what the vendor said, not the Eaton engineer). I swear the manufacturer shouldn't be able to advertise that it can take 70amps of solar if it really can only accept 56amps....

What I did with my 200amp panel was install a 150A main breaker in place of the 200A main . House had run fine on the old 100amp panel with a sub panel for 30 years so no concerns about "only" having a 150A main. Eaton likely makes a 150A main for that panel. Then you can put in 2-40A breakers one for each inverter.

[bcroe]

One more thing to consider is your line voltage. Here with 250VAC
line I have a pair of 7500 inverters each putting 30A into a 40A
breaker. If my line voltage was 230VAC, current would be close to
33A.

Most solar can only hit max power for several hours, just about
fitting into the 3 hour limit. There is no way both of your inverters
can somehow put out 35A continuously, the 40A breakers are there
to protect the line and wiring if an inverter shorts out (causing
instant disconnect). I say it is a problem with specmanship, not
a real one. Bruce Roe

[foggysail]

What I did with my 200amp panel was install a 150A main breaker in place of the 200A main . House had run fine on the old 100amp panel with a sub panel for 30 years so no concerns about "only" having a 150A main. Eaton likely makes a 150A main for that panel. Then you can put in 2-40A breakers one for each inverter.

Mike, what you did was fine although I do have to ask a question. Did you check the bus rating before changing the main breaker? I have a 200A Square D panel with a 200A main breaker. But the bus rating by Square D is 225.

[Mike 134]

Mike, what you did was fine although I do have to ask a question. Did you check the bus rating before changing the main breaker? I have a 200A Square D panel with a 200A main breaker. But the bus rating by Square D is 225.

Same with mine it's also 225. I went with 150Amp so I would not need to change out the 1-1/4 nipple that fed the old 100amp panel (would have been a PITA). This way I could use 1/0 cables in the 1-1/4. Fortunately, the utility when it wired the subdivision used all 4/0 aluminum cables for the service laterals.

[foggysail]

Been a while since we first discussed solar...............I'll make this short, want to minimize my hijack of this thread. I have my solar installed, 28 400W panels with Enphase IQ8+ inverters. Trees everywhere but it looks like I will produce 1,000KWH this month or very close to it.