5.75kw solarsystem connected to a 100 amp Panel via combiner panel ?

[logical]

100 amp panel will only take a 20 amp breaker of additional generation.

As was mentioned, if you have a 125 amp panel there would be no problem with a 30 amp of additional generation because you have a 100 amp main breaker.
The twenty percent rule would give you 125/5=25 amps additional available making a total of 125+25=150 amp total maximum. Because it would be a 125 amp panel with only 100 amp coming through the 100 amp main, you could easily accommodate 30 amps.
If as i suspect from your statements, it is a 100 amp panel with a 100 amp breaker, it can only accommodate a 20 amp breaker for generation.
An upgrade to 200 amps if your incoming wire will allow would bring your house to modern standards and allow 40 amp breaker for generation.
$1200 to $1500 is a fair and good price for the change over.
By the way, if your panel is a Zinsco panel, it would be wise to change for safety reasons. Zinsco is no longer manufactured and they are known to not break causing fires.

[josh26757]

There was a misconception when I first wired mine and they suggested this setup, but it would have resulted in needing another inspection. I have a 200 amp service and it was no problem just adding it to a duel 40 amp breaker in the main panel. If I had a problem with 100 amp service I would try to connect without entering the main service panel, but I only know my state and inspector. Here they really didn't know what they were looking at, so it was no problem getting everything passed. Plus I paid a master electrician to tie it all in. Though it added $800 to the install the sound mind is worth it. I would still be surprised if they would not allow this type of connection, especially if a 100 amp breaker was added.

[inetdog]

I tried to read through all the posts and hope that this was not already mentioned, but here in WV you do not have to go through your panel box. The only difference here is they wanted a breaker panel mounted outside to handle the 300AMPs coming into the inverter, but they do not require the inverter to be directly tied to the existing panel.

Here is the link to the wiring options: https://www.firstenergycorp.com/cont...connection.pdf

You will notice close to the bottom there is an option for wiring separate from the main panel.

It has been mentioned in other threads and it is called a supply side or line side tap. It is allowed by the NEC but some POCOs will not accept it for an interconnect. To a lesser extent some AHJs have objections to it via local regulations.
Too bad they did not include a one-line diagram of it the way they did for the other interconnections, since that would have made it clearer.

[josh26757]

Alternative?

I tried to read through all the posts and hope that this was not already mentioned, but here in WV you do not have to go through your panel box. The only difference here is they wanted a breaker panel mounted outside to handle the 300AMPs coming into the inverter, but they do not require the inverter to be directly tied to the existing panel.

Here is the link to the wiring options: https://www.firstenergycorp.com/cont...connection.pdf

You will notice close to the bottom there is an option for wiring separate from the main panel.

[Itsme]

Thanx for the answers folks. That makes sense. So basically the code allows it but does not mean AHJ/Utility will.
I would love to upgrade my panel but I got a quote of $1250 for a new 200 amp panel, parts+labor with a new line to the meter vs $180 for just two 20 amp breakers and the necessary wiring.

This a fair chunk of change I would like to avoid.
My average loads are well below 100 amp.

BTW, the $1250 is a good price for a panel upgrade. Also, if you do it for solar install, you can claim 30% credit on that, I am told.

[inetdog]

Thanx for the answers folks. That makes sense. So basically the code allows it but does not mean AHJ/Utility will.
I would love to upgrade my panel but I got a quote of $1250 for a new 200 amp panel, parts+labor with a new line to the meter vs $180 for just two 20 amp breakers and the necessary wiring.

This a fair chunk of change I would like to avoid.
My average loads are well below 100 amp.

The best way to make the decision in your case will be to get an opinion in advance from the AHJ (Authority Having Jurisdiction) and your POCO instead of having an electrician do the 100A panel connection and then failing an inspection.

I do not find it at all unlikely that you could stay with a 100A service for your normal house loads.
BTW, it is not the average load but the peak load that governs the service size, but the NEC calculations always tend to overestimate the load.

[dusty144]

Thanx for the answers folks. That makes sense. So basically the code allows it but does not mean AHJ/Utility will.
I would love to upgrade my panel but I got a quote of $1250 for a new 200 amp panel, parts+labor with a new line to the meter vs $180 for just two 20 amp breakers and the necessary wiring.

This a fair chunk of change I would like to avoid.
My average loads are well below 100 amp.

[inetdog]

After some investigation turns out that I have a 125 amp panel that has already been de-rated to 100 amp main breaker.
Does this mean I can use the 25 amp panel derate + the 25 amp of the 120% rule (125 ampx.2 = 25 amp) for a total of 50 AMP.
My Electrician has been able to squeeze two more spots out of my panel by removing some breakers I don't use.
I only need to put in 2x20 amp breakers for my 2 strings. But want to get the logic correct.
So I don't need to replace my panel with 200 Amp right?

Appreciate any comments.

According to the National Electrical Code, as long as you PV backfeed breakers are at the bottom end of the panel bus, as far as possible from the main, the PV breaker sizes can add up to (125 x 1.2) -100, or 50 Amps. In NEC revisions before [2014] that explicitly limits the breaker amperage and the actual GTI nameplate maximum output, if lower, does not help you.

However, the fact that the NEC allows it does not mean that a local inspector or power company (POCO) will not give you grief about it based on (100 x 1.2) -100.

In Los Angeles, for example, LADWP will try to tell you that even without taking PV into consideration the fact that you have a 125A panel means that you cannot have only a 100A service regardless of the size of the main breaker.

[Itsme]

In San Jose, with a 100 amp panel i was not able to get a system larger than 3.8KW. Something about no more than 20% of the panel load. So, i had to upgrade panel to a 200 amp, to get a 5.72 KW system installed.

You can also ask the installer to consider a line side tap....if they can; then the panel is bypassed.

Thanks

[dusty144]

After some investigation turns out that I have a 125 amp panel that has already been de-rated to 100 amp main breaker.
Does this mean I can use the 25 amp panel derate + the 25 amp of the 120% rule (125 ampx.2 = 25 amp) for a total of 50 AMP.
My Electrician has been able to squeeze two more spots out of my panel by removing some breakers I don't use.
I only need to put in 2x20 amp breakers for my 2 strings. But want to get the logic correct.
So I don't need to replace my panel with 200 Amp right?

Appreciate any comments.

[dusty144]

Volusiano thanx for taking the time.

Sorry I should have been a bit clearer. My dryer went from Electric to Gas which is why I think my panel has quite low load. Also I have converted all my lighting to CFL including a 2400 Watt incandescent with 30+ fixtures to track light to CFL. My big load is a large A/C system upsized to cool the garage and basement, for my wife. But the A/C is fed through a separate breaker outside.

I'm fortunate that my panel definitely says 125 AMP max on a sticker inside, even though my main breaker is only 100 AMP.

[wanabefree]

Eliminating circuits and removing breakers may make room on the panels if you're out of breaker space, but that wouldn't help with the 120% rule, would it? I assume the rule has to do with the bus bar size and not the amount of breakers you have on it.

If your panel is full up, can't you replace some of the larger breakers that take 2 full slots with a half-size kind that will take only 1 slot to make room?

So from all this discussion so far, I assume that derating the service panel to 75A is not an option for 100A panels or something (since it was never mentioned here so far as an option)? Especially in your case, Dusty144, since you said your loads are so low.

I believe that derating the Panel to a 75s or 80a main breaker is technically possible but might be a little tricky selling it to the code compliance officer. A line side tap is the most feasible cost effective alternate but also not aloud by some municipal codes. I just hope in my case my Panel is actually a 125a buss but only a 100a main but without finding any markings or tags on or inside it makes it hard to verify.

I talked to my salesman again about my concerns and he told me they will submit it for approval as per there original design and if the city rejects it they will do what ever is required to make it meet cod at no additional cost to me. So i guess I just have to wait and see what happens next.

[Volusiano]

Thanx for posting this.

I'm in the exact same position. Hopeful to avoid the 200AMP upgrade. I don't have an engineer yet but hope to do the exact same thing of attaching a 60 AMP sub panel. My service too per the electrician is 200 AMP.

My loads are so low that I'm not even sure 100 AMP is needed yet my panel too is full up. I have half a mind to eliminate the dozen or so outlets I have not used in 20 years in this house. But tracing the lines would be expensive.

Any suggestions would be appreciated.

Eliminating circuits and removing breakers may make room on the panels if you're out of breaker space, but that wouldn't help with the 120% rule, would it? I assume the rule has to do with the bus bar size and not the amount of breakers you have on it.

If your panel is full up, can't you replace some of the larger breakers that take 2 full slots with a half-size kind that will take only 1 slot to make room?

So from all this discussion so far, I assume that derating the service panel to 75A is not an option for 100A panels or something (since it was never mentioned here so far as an option)? Especially in your case, Dusty144, since you said your loads are so low.

[dusty144]

Thanx for posting this.

I'm in the exact same position. Hopeful to avoid the 200AMP upgrade. I don't have an engineer yet but hope to do the exact same thing of attaching a 60 AMP sub panel. My service too per the electrician is 200 AMP.

My loads are so low that I'm not even sure 100 AMP is needed yet my panel too is full up. I have half a mind to eliminate the dozen or so outlets I have not used in 20 years in this house. But tracing the lines would be expensive.

Any suggestions would be appreciated.

[wanabefree]

Actually you are limited on a backfeed breaker to 120% of the buss bar rating.
If you can find the model # of your panel and the manufacturer you may be able to determine the buss bar ratings from them (hint look inside the panel for the label by taking the cover off)

I have looked inside the panel several times and not found any make model or brand information but I ma going to take a look again tomorrow. I was told by a friend that it is highly possible that the buss bar is actually a 125 amp rated as most 100 amp panels do not have removable main breakers and are fixed or fused to the bus bar. maybe that is what they are thinking also as they did do a visual inspection but at the time said that all they could go by is the main breaker rating as they did not see any labels or rating stamps either.
I kinda want them to replace the panel just because it could be beneficial in the future but it would add about $1500 cost to the system.