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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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Should not be more than 50 amps. The calc should 200 times 120% minus 50 amps equals 170 left for the service.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

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That's why I have to go with a 400A serviceShould not be more than 50 amps. The calc should 200 times 120% minus 50 amps equals 170 left for the 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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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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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 discoren79eg said:

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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.ren79eg said:True...just tryuing to figure out where the previously mentioned 50 came from.

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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.

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.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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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.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.

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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.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.

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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.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.

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II. Utility-Interactive Invertersbackstay 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.

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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Too bad, systems rarely increase in size because module manufacturing changes too rapidly to match new panels to old ones.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.

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