Northeast USA -- roof-mount or put in attic?

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jazzer
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My RE system: PS2 with GVFX3648, MX60, Mate (v4.2.1), FN-DC, 327AH AGM 48V battery banks [234AH EV185A-A, 93AH UPS12-350MR], 3470W mixed modules composed of 6 strings in 56-60V nominal (83Vmp) configuration
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Northeast USA -- roof-mount or put in attic?

Post by jazzer » Sat Jun 23, 2007 9:12 am

I live in NH (43┬░N latitude) where we get a lot of snow. I was planning to vertically mount the PSPV box to a pipe (existing roof penetration). The roof is 6.5:12 so it could be mounted directly to the roof but I was concerned about snow accumulation so I opted for the vertical mount. Naturally I plan to use only USE-2 intermodule wiring.

The thought has crossed my mind to mount the box in my attic, just on the other side of the roof penetration. Of course it would be easier to access and I wouldn't have to worry about snow, but in the summer it would be exposed to higher temperatures. There are 6 strings of 48V-nominal wired panels, so that's more wiring to bring inside too, rather than just the PSPV output. Then again I don't know what NEC has to say about this. I'm no expert on NEC code either -- I'm learning as I go.

I was just wondering what you experts think about these options or if you have some alternate suggestions.

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crewzer
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Post by crewzer » Sat Jun 23, 2007 2:10 pm

Jazzer,

IÔÇÖm not an NEC expert by any means. So my comments may need confirmation.

NEC 690.14 says that a photovoltaic disconnecting means shall be installed at a readily accessible location either outside of a building or structure or inside nearest to the point of entrance of the system conductors. The photovoltaic disconnecting means shall not be installed in bathrooms. IÔÇÖd wonder if your inspector would consider the attic to be a ÔÇ£readily accessible locationÔÇØ.

On a separate but related note, you may want to take a look at NEC 690.5, which addresses the requirement for ground fault protection for arrayÔÇÖs mounted on a dwelling.

You may John Wiles' articles on PV installations and the NEC to be helpful. See: http://www.nmsu.edu/%7Etdi/Photovoltaic ... -Stds.html Additionally, this guide might be useful: http://www2.fsec.ucf.edu/en/education/c ... or_NEC.pdf

HTH,
Jim / crewzer
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Post by sparky » Sun Jun 24, 2007 6:14 am

Yea, what Jim said and ask your building department. They will be the ones who inspect it! If they are good they will know but if they are not you will have "show" them the way. Put a thermometer up there and get some data now that we just past the Solstice.

I tend to think that it is not the way to go but.........

Martin
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Post by Martin » Sun Jun 24, 2007 8:42 am

Definitely talk to your building department as Sparky says. The definition of 'readily accessible' usually means that the box has to be mounted in a location where there is a seven foot clearance floor to ceiling, and there are no obstructions for three feet in front of it. The clearance floor-to-ceiling has to be maintained to three feet from the box, too. The intent is that someone who is servicing the panel should be able to easily stand right in front of it.

I got dinged on that one because I mounted my PSPV on an array pole. They ended up letting me leave it there after I appealed for a variance, but I would have done it differently had I thought it through in the beginning.
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halfcrazy
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Post by halfcrazy » Sun Jun 24, 2007 3:23 pm

my understanding of the code is that the combiner can be considered just that and not a disconnect so it can go on the roof or what ever but if you do that the pv wiring has to be in rigid metallic conduit till it gets to the disconnecting means witch has to be readily accessible.
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