What size breaker do you use in main panel with Sol-Ark 12K?

SolarHead

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I used a 60A breaker in my main panel , but wondering about the 120% rule on breakers. Sol-Ark mentioned I may should be using a 40A breaker instead. Anyone using a Sol-Ark 12K, what size breaker are you using in your main panel? This is the dedicated breaker for the Sol-Ark to get its AC power, as well as push back through to push power onto the main panel (if you are using "limited power to home" mode).

One reason I went with 60A breaker was because the Sol-Ark 12K can handle I think up to 63A pass-through. But then I worry about the 120% rule on breakers.

Thinking about the fact that a solar PV or battery energy storage system can supply additional power from the opposite side of the main breaker supply. There are now two separate sources feeding power from opposite ends and no single protection device that prevents the electrical equipment in the middle (bus bar in this case) from becoming overloaded. In this example, there is a total of 250 amps of power draw that would exceed the safety rating of the busbar, allow it to heat up becoming a serious fire hazard.

The NEC 120% rule limits the size of additional power sources (PV or battery) to within an acceptable safety limit based on the equipment label rating. In this case, the PV breaker would be limited to a maximum of 40 amps. 200 amp rating x 120% = 240 amps 240 amps minus the 200 amp main breaker = 40 amps max for PV breaker

Your thoughts?
 

RV10flyer

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I'm totally off grid. I am feeding a 100 amp panel with two 50A breakers from two Sol Ark 12K's. Then from 100A breaker into 200A transfer switch on to house.
 

SolarHead

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I should have stated, I'm grid-connected. So my main panel has 200A service, but as you know I would/should not be putting that much on the bus bars. Probably 100A at the most when heat pump inrush current (start up) occurs. I think the 60A breaker on the same main panel that the Sol-Ark is pushing into (when selling to the grid and/or assisting load) should be okay. I just wondered if anyone thinks I should use a 40A breaker instead.
 

Wet1

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I'm not 100% up to speed on the 120 rule, but doesn't it say you're allowed to exceed the TOTAL load up to 120%? In your case that's up to 240A total. What I don't think I saw was how much is already installed in the panel. If I'm understanding it correctly, if you had a 200A panel, but only had say 170A of breakers installed in it, you'd have no issue installing the optimal 60A breaker and be well under the 240A max. If the panel already has 200A of breakers installed, then it would seem you'd need to limit it to 40A to be legal (although, would an inspector have an issue with only a 40A breaker on a device that could easily exceed that?) Am I correct in my understanding of the rule and total installed capacity?

Another option would be to install a sub-panel, correct?
 

bertiojones

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If you are utilizing the entire 63 amps of passthrough into a critical loads panel you want to make sure your total continuous load (don't just add up the breakers but do the calculations) doesn't exceed 60 amps.

I would have a 60 amp breaker in my main panel and a 60 amp breaker in my critical load panel.

Size your wire to your Inverter for 75 amps and the wire from the inverter to the critical load panel for 75 amps.

You would then need to derate your main breaker to 175 amps to free up 65 amps of room.

(I went back and forth on what to size the breaker for the critical load panel. Cautiously you could do 50 amp breaker and size your wire from the inverter to the critical load panel for 60 amps but I think keeping everything at 60 amps is what Sol-Ark is wanting you to do being they have the inverter with a slightly higher breaker rating 63 amps)

Also when derating your main some AHJ's require load calculations that make sure dropping your main breaker capacity to 175 amps will be sufficient. Usually when people run a critical load panel they are taking loads off the main panel so the net gain of loads is zero.
 
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SolarHead

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My main panel I have a 60A breaker, that provides AC to Sol-Ark 12K

My critical loads panel has no breaker. I connected 4ga wire from Sol-Ark LOAD over to Critical Loads panel and direct to the lugs to the bus bars in the breaker box. For my critical panel, I got a SquareD breaker box, identical to my main panel. That way I could move breakers over and they fit.
 

bertiojones

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So you are using the 63 amp breaker on the Sol-Ark as your Critical Load Panel breaker.

Then you just need to derate your main breaker to be under the 120% rule for backfeeding into the main panel. The next size down would be 175 amps main breaker.

The inverter would only ever push 9000 watts to the main panel which is 37.5 amps.

1.2x of 37.5 is 45 amps so you are over your limit of 40 amps on the main breaker.
The idea is in a perfect storm your main service is pushing 200 amps and your inverter is pushing 45 amps which is over the 240 amps (120% rule) for the bus on the main panel.

Now if your not getting any of this permit'd then you will be fine. If you are trying to do it to code then you will need to derate.
 

SolarHead

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thanks. That makes sense. I think all I'd have to do (based on your info) is derate , take my main service panel main breaker (200A) and replace it with a 175A breaker and I'd be within code.

I found this page online and it helped me think about it a bit more.
 

SolarHead

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But keep in mind, my 200A main service panel, it has more than 200amps worth of breakers in it. I have never added the breakers amperage up , but I'm sure its over 200A. I don't know what inspection or code would be, I mean, how much breaker can you install in a 200A breaker panel and still be within code? Is it 240 amps worth of breakers? I would think its quite a bit more but again I have never added them all up. Mathematically and based on the elec code, the 120% rule applies , I think. But in reality, you're not going to use all circuits/breakers in the service panel at once. I think the highest load is around 110A draw when my heat pump starts up. Most of the day or time though I think my main service panel hovers right around 10A to 35A total. So then having the 60A breaker, and the Sol-Ark never pushing back to the main service panel more than 37.5A , I should be fine. But I could derate main breaker to 175A to feel better about it. Kind of tempted to switch the 60A breaker I installed for the Sol-Ark out for a 40A breaker instead. That still doesn't get me below the 240 you mentioned.

What do you think? replace the 60A with a 40A, and derate main breaker by replacing the 200A with a 175A. That would probably be the best plan.
 

bertiojones

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For recording usage you don't add up your breakers as not all loads are continuous. There is a giant formula on how to factor in loads compared to main service to be under 80% listed in NEC (I will try and find it)

The backfed breaker serves three purposes.
1)To feed the inverter in order to charge batteries. That would be this section:

1653086637982.png
If you charged at a continuous 185 amps DC (48v but the charge voltage would be around 56v) that would put you at 10360 watts.
Convert that from DC to AC with losses would get you around 40 amps at 240v. 1.2x of that would be 48 amps.

2)To be fed by the inverter to power the main panel. That would be this section:
1653086907591.png

The inverter can only push a max of 9000 watts AC to the Main panel at a maximum of 37.5 amps. 1.2x of that would be 45 amps.

3)To feed power to the critical loads panel directly through the inverter (Passthrough). That would be this section:
1653087096518.png
Hypothetically you can passthrough as much power as your wiring and breaker and CLP can take but we are limited to 63 amps internally of the Sol-Ark in which that power is passing through. Since that is the max amp before the breaker triggers we would want 63 amps to be our 1.2x number so we divide 63 by 1.2(instead of multiply) to get 52.5 amps. 52.5 amps would be our maximum load for continuous operation.

Now that we have all 3 of these numbers we see which parts apply to you and use the largest amperage that does.Perhaps you're not charging a battery or doing AC passthrough to a CLP (I don't have a CLP)

In your situation passthrough is your highest amperage at 52.5 amps so you would use the next up breaker of that and wire that supports that breakers size in this case 60 amp breaker and wire that supports 60 amps (4awg is good)
Derating only applies when we are pushing power to the panel not pulling so we would use the numbers for the inverter at 45 amps. You already have a 60 amp breaker for passthrough so you are covered but you need to derate as 200 amps x 1.2 ='s 240 and you need 245. Some AHJ's don't care about the actual wattage of the device putting in and only look at the capacity for derating so by having that 60 amp breaker they expect you to have account for that 60 amps (Instead of just 45) on the panel. Either way the next step down for a main breaker is 175 amps which frees up 25 amps from service and you still have the 40 extra you are allowed for a total of 65 amps of capacity.

Short version.
Derate to 175 and keep your 60 amp breaker.
 

Wet1

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Good info, thanks!
So what about just going off-grid using an interlock on the main panel? I'm assuming the 120 rule no longer applies and you use the standard max panel rating?
 

bertiojones

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Good info, thanks!
So what about just going off-grid using an interlock on the main panel? I'm assuming the 120 rule no longer applies and you use the standard max panel rating?
Depends on the AHJ. If you had an interlock you could argue that both circuits would never be energized at the same time so it shouldn't apply. Some AHJ's would want you to derate if your main panel is tied directly fed from service. When it comes to what you can and can't do the AHJ tends to have the authority.

I've seen AHJ's not allow IMO switches and require lever throw switches even then the IMO's are better for DC.

I've seen AHJ's require sch 80 even though the pipe is wall mounted above any point of contact.

I've seen AHJ's require copper on certain circuits instead of aluminum "Just because its safer"
 

SolarHead

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Although I think I might replace my 200A main breaker with a 175A breaker. I don't foresee a problem leaving things like I have it, knowing the loads I am pulling on my main box, and mindful of adding the max (37.5A) that the Sol-Ark 12K could ever push to it. I guess someone elses situation could be different but I doubt I will ever get above 120A on my main panel (adding the loads I have + the 37.5A from Sol-Ark).
 

FightThePower

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Your 60amp breaker is fine. The sol ark only sells back 37A so you are not violating the 20% rule on the bus bars (assuming its a 200A panel). Keep the 60 breaker so you can pass through 60 to your critical load panel.
 

TravisSolartrician

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A way around the 120% rule, do a loadside tap on the meter socket outside using milbank K4977 lugs, it was actually a preferred method from my power company, but they would have to come out and kill the meter to make that happen, note the double stacked lugs on the bottom, if you come of those you need to hit a service rated fused disconnect , which would have to be bonded like a separate service. There is alot of demand for the K4977 lug kits, they are very hard to find
 

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