Does main breaker count for bus rating

[Donna1]

We have a residential installation where we want to have one 200amp panel serve the house loads and install another 200 amp panel to interconnect 3-20amp and 2-15amp wind turbines for grid connect behind the meter. Both panels will be located beside each other on the outside of the building.
There will not be any loads served from the interconnect panel and a label will be installed on the panel stating "NO LOADS SHALL BE FEED FROM THIS PANEL"

Per 705.12 D2 the sum of the oc devices supplying power to the busbars shall not exceed 120%. Some have said I must count the rating of the main breaker in the interconnect panel thus only leaving me the abiltity to have 2-20amp back feed breakers . My position is that 705.12D states that the distribution equipment must be capable of supply loads in addition to the backfeed breakers before you must count the main breaker as part of the bus sizing.

Advise you thougts.:?

 

[jaggedben]

If you are going with a 200A panel, you really don't have a problem, regardless of the interpretation of 705.12(D), because you can feed your wind panel with a 100A breaker and not exceed the panel rating, let alone 120% of it. (I just hope you haven't already ordered a 200A panel with a factory installed 200A main breaker.)

Now if your question is whether you can use a smaller panel (say, 100A) then the answer is different. You will have to ask your AHJ if your proposed label is good enough for him. Some AHJs will interpret 'capable of supplying loads' very conservatively and tell you that just because you put a label on it doesn't mean that someone can't go in and install some loads there. Some some will say that your 'distribution equipment' is 'capable of supplying multiple branch circuits or feeders or both', regardless of how you are actually are using it. Some will say that by connecting all those wind turbines you actually are 'supplying multiple branch circuits'.

Most of the literature I have read and the people I've talked to suggest that the code writers intended the main breaker to be counted in all such cases. But not everyone may interpret things that way. See also the discussion I had with ggunn at the end of this thread: http://forums.mikeholt.com/showthread.php?t=140547

Also, if you end up not counting the main breaker, it would best, just common sense wise, and possibly per 705.12(D)(7), to stick with 100% of the busbar, not 120%. Fortunately for you 90A makes that easy with a 100A panel.

 

[ggunn]

I'll just add that my company has installed many systems in various jurisdictions with dedicated AC combiner panels without encountering any problems, but as jaggedben says the code is open to interpretation on this issue and just because some AHJ's have OK'ed this practice does not necessarily mean that they all will.

 

[Marvin_Hamon]

As others have said it is open to interpretation by the AHJ. The NFPA CMP that is responsible for that section of the code has been very clear in the past that they do not believe that a dedicated AC combiner should be allowed an exemption from 705.12(D)(2) because it only contains back fed breakers and has "do not add loads" signage.

Myself and others have tried for many code cycles to get specific wording added to the code to allow for dedicated AC combiners to be sized just for the back feed sources and have been rejected by the CMP every time with comments about how any distribution equipment that can contain back fed breakers can also be used to supply a load, even one that is fully populated can have a source removed and a load added. This is the same thought process that includes some conductors in the 705.12(D) requirements because someone might, someday, tap a conductor for a load. I don't agree with this myself and think dedicated AC combiners are safe, but when I use one I do an alternative methods and materials request to the AHJ and have them specifically approve the use and not just assume if the plans checker does not ask about it that it is approved. At least if someone hauls the installer into court years later and says it is a code violation I can show that the AHJ specifically approved it.

 

[PURE]

thougthts

thougthts

Advise you thougts.:?[/QUOTE]

It would seem to me that the easiest answer would be to keep your 200amp busbar panel,(main lug panel would be better)but only connect it with a 100 amp main snapped on the buss, this would allow all your math to work out.