1. Originally Posted by cowboyjwc
Ok if you really read that section it only talks about the location of the solar breaker, also if you have a 200 panel + 90 amps of solar + everything else I'm guessing that 90% of the time you are going to exceed the busbar rating. Now if you go with one of the new solar panels with the 225 amp bus and a 150 amp main, the amount of solar you can put in is almost unlimited, to a point of course.
That subsection states, in part, "The sum of the ampere ratings of all overcurrent devices on panelboards, both load and supply devices, excluding the rating of the overcurrent device protecting the busbar, shall not exceed the ampacity of the busbar." The underlined part is the MCB. Load device are load breakers. Supply devices is subjective. I believe there's somewhere that states you can use 125% of inverter output rating(s) for upstream determinations... anyone?

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Originally Posted by Smart \$
That subsection states, in part, "The sum of the ampere ratings of all overcurrent devices on panelboards, both load and supply devices, excluding the rating of the overcurrent device protecting the busbar, shall not exceed the ampacity of the busbar." The underlined part is the MCB. Load device are load breakers. Supply devices is subjective. I believe there's somewhere that states you can use 125% of inverter output rating(s) for upstream determinations... anyone?
The way it's written you use 125% of the inverter nameplate rating for 705.12(D)(2)(3)(b) but the solar breaker rating for 705.12(D)(2)(3)(c). Of course, you can use different sections for different panels in series.

3. Originally Posted by cowboyjwc
705.12(D)(2)(3)(b) says exactly what I said. Where two sources, one utility and the other an inverter, are located at opposite ends of the busbar that contains loads, the sum of 125% of the inverter output circuit current and the rating of the overcurrent device protection the busbar shall not exceed 120% of the ampacity of the busbar.

We only have all in one panels here so the main service panel will always contain loads.
Sorry, I misunderstood. I thought thought there was only one panel, the service panel with 400 bus with a 200 amp main breaker

But I still dispute that that is "exactly" what you said. You left out the "ampacity of the busbar" part sorry to nitpick, but that made it seem you were interpreting the rule differently.
Last edited by electrofelon; 09-20-17 at 07:52 PM.

4. Originally Posted by electrofelon
Sorry, I misunderstood. I thought thought there was only one panel, the service panel with 400 bus with a 200 amp main breaker

But I still dispute that that is "exactly" what you said. You left out the "ampacity of the busbar" part sorry to nitpick, but that made it seem you were interpreting the rule differently.
Oh you can nitpick all you want, I'm married with children. No what I have is a 200 amp panel with a 200 amp bus bar feeding a 400 amp panel.

Or to reexplain it in solar terms, solar array to inverters, inverters to 90 amp solar breaker in a 400 amp panel with a 200 feeder, to a 200 amp main service panel/load center with a 200 amp bus.

5. Cowboy,
Maybe I am missing something. Why don't these folks just add a new meter for the solar?

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Originally Posted by Sierrasparky
Cowboy,
Maybe I am missing something. Why don't these folks just add a new meter for the solar?
POCO may not be willing to add another meter, especially if the state has Net Metering laws.

7. Originally Posted by GoldDigger
POCO may not be willing to add another meter, especially if the state has Net Metering laws.
Cowboy is in Southern CA.
To the best of my recollection the POCO there will allow a separate meter.

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Even if the utility allows it without extra fees and charges, which I doubt, adding another meter is a huge extra expense compared to a load side connection.

Also Cowboy mentioned batteries and if the intention is to island with solar power to when the grid goes down, that ain't gonna work if the power and loads are on separate meters.

9. Originally Posted by cowboyjwc
Oh you can nitpick all you want, I'm married with children. No what I have is a 200 amp panel with a 200 amp bus bar feeding a 400 amp panel.

Or to reexplain it in solar terms, solar array to inverters, inverters to 90 amp solar breaker in a 400 amp panel with a 200 feeder, to a 200 amp main service panel/load center with a 200 amp bus.
(2) Bus or Conductor Ampere Rating. One hundred twentyfive percent of the power source output
circuit current shall be used in ampacity calculations for the following:
(1) Feeders. Where the power source output connection is made to a feeder at a location other than the opposite end of the feeder from the primary source overcurrent device, that portion of the feeder on the load side of the power source output connection shall be protected by one of the
following:
a. The feeder ampacity shall be not less than the sum of the primary source overcurrent device and 125 percent of the power source output circuit current.

200A primary source overcurrent device in 200a panel feeding 400 a panel with 200 amp feeder(250 ser al??? 3/0 cu thhwn? ????) 400 amp panel has 90a PV source(125% of output circuit) Yes?????
would that make the feeder required to be rated @ 290 amps??? Just thinking outside the box in this unusual circumstance.

10. Originally Posted by mwm1752
(2) Bus or Conductor Ampere Rating. ....
That's from the 2011 edition. He's under the 2014 NEC I believe and the changes have some significant requirement impact.

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