AC combiner alternative

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ggunn

PE (Electrical), NABCEP certified
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Austin, TX, USA
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Consulting Electrical Engineer - Photovoltaic Systems
A colleague of mine has suggested an alternative to a traditional load center for combining AC power from inverters, and at first blush I don't see a problem with it. He has suggested that we build an enclosure with busbars rated per 705.12(D)(2)(3)(c) and install case mounted breakers in the enclosure with conductors and lugs feeding the busbars. Is there any reason why this would not fly?
 
Even if it would fly, why would you even consider going this route?

In my experience, custom costs more.
 
ggunn said:
A colleague of mine has suggested an alternative to a traditional load center for combining AC power from inverters, and at first blush I don't see a problem with it. He has suggested that we build an enclosure with busbars rated per 705.12(D)(2)(3)(c) and install case mounted breakers in the enclosure with conductors and lugs feeding the busbars. Is there any reason why this would not fly?
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Not technically listed as an assembly, unless you get a custom shop to build it.

If it were up to only me, I would approve it if all active components are listed, used per manufacturer's specs, and presented no safety hazards. But usually AHJ's require a listing as an assembly on devices that combine circuits.
 
Smart $ said:
Even if it would fly, why would you even consider going this route?

In my experience, custom costs more.
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It's purely academic at this point. Whether it would be more expensive isn't an issue.
 
I don't get it. What's 'alternative' about it? Wouldn't it still be a panelboard under the NEC definition?

Is this to handle breakers that are larger than can be installed in typical load centers?
 
ggunn said:
A colleague of mine has suggested an alternative to a traditional load center for combining AC power from inverters, and at first blush I don't see a problem with it. He has suggested that we build an enclosure with busbars rated per 705.12(D)(2)(3)(c) and install case mounted breakers in the enclosure with conductors and lugs feeding the busbars. Is there any reason why this would not fly?
Click to expand...

Would the busbars be fabricated? Is that allowed? How would they be sized?
 
Carultch said:
I think what Electrofelon means, is how would a given desired ampacity be cross referenced to the required geometry?
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There are tables where you can map bus ampacity to geometry, but if it were I doing this I would defer to a fabrication house that routinely deals with secondary bus enclosures.
 
Carultch said:
I think what Electrofelon means, is how would a given desired ampacity be cross referenced to the required geometry?
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Not covered under the NEC... so listing would be the only alternative I see regarding approval by AHJ.

Legrand has a fairly comprehensive guide for 250A and up.
http://www.legrand.com/files/fck/File/pdf/Power_guide/EX29016.pdf

Here's one that gets into the math and geometry...
http://www.leonardo-energy.org/sites/leonardo-energy/files/Cu0184-rating.pdf
 
electrofelon said:
Right, that's what I was getting at. Can you make your own conductor out of bus bars? I don't think so
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I've seen it done on projects for transitions from bus duct to switchgear or transformers. A fair many projects were power plants not under NEC pervue by law but typically by project spec's. A couple steel mills, and one school. Uncertain of approval process for the latter.
 
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