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Discussion Starter #1 (Edited)
Having to install a 400A service change for the Solar Electrician because of the rating of the existing 200A service bus, and the "Main Breaker's Top fed rule" Customer has a center fed main.

Looking for the code reference if anyone knows it.
 

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Discussion Starter #4
Do a line side tap, much cheaper and easier.

I'm just doing the service change for the Solar co. They have another Electrician doing the invertors, and the rest.

Explain please what you mean by line side tap. Existing is a 200A, and the Solar 2 pole is going to be a 70A 12kw system
 

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dronai said:
I'm just doing the service change for the Solar co. They have another Electrician doing the invertors, and the rest.

Explain please what you mean by line side tap. Existing is a 200A, and the Solar 2 pole is going to be a 70A 12kw system
Should not be more than 50 amps. The calc should 200 times 120% minus 50 amps equals 170 left for the service.
 

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Discussion Starter #6 (Edited)
Should not be more than 50 amps. The calc should 200 times 120% minus 50 amps equals 170 left for the service.
That's why I have to go with a 400A service

Also how did you come up with 50A ? 120% x 200 = 240 I thought that means the remaining 40 is the maximum amount that could be used ?
 

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Discussion Starter #8
12kw = 50 [email protected] However I think you're right about the 40 amps in addition to the 200 amp main breaker
The guy ran 2 invertors into a panel backfeeding with 2 35A 2 pole breakers, and then #4cu, to a main disconnect that will tie into the main panel.

I didn't check his math but it looks like more than 12K
 

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FWIW - You don't necessarily "need" a 400 amp service. In addition to doing a line side setup, you could swap in a panel with a 250 amp BUSS rating and use a 200 amp main breaker. IF you could source the parts. That would allow for 100amps of inverter backfeed.
 

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ren79eg said:
12kw = 50 [email protected] However I think you're right about the 40 amps in addition to the 200 amp main breaker
It's actually 62.5 amps. You have to rate it for continuous load. Each 6kw inverter is rated at 31.25 so the next breaker size is 35. I agree that a 400 amp service is overkill I would do a 250a with a 200a main or main lug panel with a seperate disco
 

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ren79eg said:
True...just tryuing to figure out where the previously mentioned 50 came from.
12kW divided by 240 volts is 50 amps. Is that the solar array size or are you calling it 12kW because of the inverter? With losses across the system you will not see that many amps. If the calculated load of the service is less than 170 amps, I say a 200 amp service is enough.
 

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Discussion Starter #13
FWIW - You don't necessarily "need" a 400 amp service. In addition to doing a line side setup, you could swap in a panel with a 250 amp BUSS rating and use a 200 amp main breaker. IF you could source the parts. That would allow for 100amps of inverter backfeed.
Yep, but two supply houses and a lot of calls, and I couldn't even get a panel with 225A busing ! It has to be a top fed main breaker, and not center fed. That is what will give me the 120% rule to work with. They only had 200A, and then 400A top fed breaker panels.

12kW divided by 240 volts is 50 amps. Is that the solar array size or are you calling it 12kW because of the inverter? With losses across the system you will not see that many amps. If the calculated load of the service is less than 170 amps, I say a 200 amp service is enough.
I don't know their load calcs. But I went through it with the inspector already, as far as my requirements, and what he was looking at with the invertors, and the existing panel. The Solar company is now in the process of submitting plans, and getting permits.
 

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backstay said:
12kW divided by 240 volts is 50 amps. Is that the solar array size or are you calling it 12kW because of the inverter? With losses across the system you will not see that many amps. If the calculated load of the service is less than 170 amps, I say a 200 amp service is enough.
Unfortunately most inspectors I've dealt with and engineers don't care about the losses on the system or the calculated load. If the inverters rated output is 12kw they want it calculated and installed as such. That would mean a minimum of 70a ocpd and a 250 rated buss with 200a main breaker.
 

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ElectricJoeNJ said:
Unfortunately most inspectors I've dealt with and engineers don't care about the losses on the system or the calculated load. If the inverters rated output is 12kw they want it calculated and installed as such. That would mean a minimum of 70a ocpd and a 250 rated buss with 200a main breaker.
Inverter size has little to do with system generating capability. It a means to transfer energy from generator(panels) to the grid. Inverters are almost always larger than the array that they connect to.
 

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backstay said:
Inverter size has little to do with system generating capability. It a means to transfer energy from generator(panels) to the grid. Inverters are almost always larger than the array that they connect to.
I understand what your saying and all I'm saying is they don't care about that. The system must be wiring according to the output of the inverter.
 

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backstay said:
Inverter size has little to do with system generating capability. It a means to transfer energy from generator(panels) to the grid. Inverters are almost always larger than the array that they connect to.
II. Utility-Interactive Inverters
705.60 Circuit Sizing and Current.
(A) Calculation of Maximum Circuit Current. The maximum current for the specific circuit shall be calculated in accordance with 705.60 (A)(1) and (A)(2).
(1) Inverter Source Circuit Currents. The maximum current shall be the maximum rated input current of the inverter.
(2) Inverter Output Circuit Current. The maximum current shall be the inverter continuous output current rating.
(B) Ampacity and Overcurrent Device Ratings. Inverter system currents shall be considered to be continuous. The circuit conductors and overcurrent devices shall be sized to carry not less than 125 percent of the maximum currents as calculated in 705.60(A). The rating or setting of overcurrent devices shall be permitted in accordance with 240.4(B) and (C).
Exception:  Circuits containing an assembly together with its overcurrent device(s) that is listed for continuous operation at 100 percent of its rating shall be permitted to be utilized at 100 percent of its rating.
 

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ElectricJoeNJ said:
II. Utility-Interactive Inverters
705.60 Circuit Sizing and Current.
(A) Calculation of Maximum Circuit Current. The maximum current for the specific circuit shall be calculated in accordance with 705.60 (A)(1) and (A)(2).
(1) Inverter Source Circuit Currents. The maximum current shall be the maximum rated input current of the inverter.
(2) Inverter Output Circuit Current. The maximum current shall be the inverter continuous output current rating.
(B) Ampacity and Overcurrent Device Ratings. Inverter system currents shall be considered to be continuous. The circuit conductors and overcurrent devices shall be sized to carry not less than 125 percent of the maximum currents as calculated in 705.60(A). The rating or setting of overcurrent devices shall be permitted in accordance with 240.4(B) and (C).
Exception:  Circuits containing an assembly together with its overcurrent device(s) that is listed for continuous operation at 100 percent of its rating shall be permitted to be utilized at 100 percent of its rating.
Too bad, systems rarely increase in size because module manufacturing changes too rapidly to match new panels to old ones.
 

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I was a sub for a solar installer for almost 2 years and performed almost 200 hundred Iinstallations. From what I have read yyour better off performing a line side tap between the meter and main breaker in home. We normally use a 18 by 18 by 6 pvc box and 3 barrel insulated lugs . We did start to use a different product that has teeth that bite onto the service.conductors Iin the panel and run out but I was never a fan of them. If you have any questions PM me.
 
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