DC Runs in the Attic [RE-wrenches]

Gary Higbee gary at windstreamsolar.com
Sun Sep 19 00:19:52 PDT 2004


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Mark and Wrenches,

Oh, yes PV through the attic. As an inspector I'm supposed to back up code, 
but most importantly make sure contractors meet the Energy Trust of Oregon 
requirements. The issue of runs through the attic is not new to Oregon, and 
I've seen several examples of local jurisdictions allowing it, not allowing 
it, or allowing it with a disconnect on the roof. I've heard of a fused 
pass-through box, too. My opinion is that PV is growing beyond a simple 
"add-on," that we need to address building integration, and that this is 
important.

At this point there are jurisdictions in Oregon I am aware of who allow PV 
runs through attic space so long as they are in metallic conduit--citing a 
'05 code change as justification.

Some thoughts (and please check me on this!):

1) The idea of a PV disconnect on the roof escapes my logic. Aren't 
disconnects supposed to be accessible? If this is as I read things then if 
there is a disconnect on the roof I expect to see a code-compliant staircase 
leading up there. Let's make sure the treads are right, folks, and those 
handrails had better be just right. Oh, watch the reach to the disconnect, 
too! Unless I see a good and/or code-requiring argument otherwise I would 
flag a DC disconnect (if that's what it is called) on the roof as a safety 
violation--unless the above stairs and rails were carefully attended to--an 
absurd proposition, of course.

2) Using a fused pass-through box is equally absurd, right? After all, by 
NEC the fuses must be sized beyond the maximum short-circuit current of the 
array. A fault will sit there and fry every day without blowing a fuse, 
won't it? What's the point here, other than to satisfy a naive electrical 
inspector?

3) Other wiring ideas? Well, I think many of us do see the potential risks 
of stapled cable of a limited current source (that might happen to be 
pierced) sizzling away against the rafter. What happens when things dry out 
enough to say goodbye to the attic, and maybe house and residents. Doesn't 
seem wise to me, and this would be a major violation in my book.

4) Using metallic conduit sounds like a step in the right direction. Let's 
say there's a nick in a wire or two, though, and a nice little arc plays 
around every day--until the EMT gets really hot or eventually burns through. 
Is this realistic, possible?

5) Is there any such thing as a DC arc-fault breaker that could go on the 
roof? Would the safest solution be an arc-fault breaker on the roof, and 
then any reasonable wiring method beyond that? In this case would not the 
stapled and/or nicked wires, or whatever might generate an arc, turn off the 
source? Is metallic conduit really a reasonable solution, or is it a 
temporary work-around until we get DC arc-fault breakers on the roof? And if 
we do that then is this considered a disconnect (and thus subject to 
accessibility)?

It seems to me that the best solution would be an arc-fault detector on the 
roof and a DC disconnect prior to the charge control (battery-based) or 
inverter, along with reasonable wiring practices through the attic or other 
enclosed space (in metallic conduit or not). This way we have a DC 
disconnect prior to the first electronics the modules meet, and importantly, 
we also have catastrophic fault protection prior to an enclosed space.

Thoughts?

Gary

*****
----- Original Message ----- 
From: "Mark Byington" <markbyington at sbcglobal.net>
To: <RE-wrenches at topica.com>
Sent: Saturday, September 18, 2004 9:15 PM
Subject: DC Runs in the Attic [RE-wrenches]

A local inspector in CA is interpreting 230.70 to mean we cannot run the DC 
line from a roof mounted PV array through the attic of a residence to the DC 
disco mounted on an exterior wall.  His justification is that the DC run is 
a service entrance conductor.  He is worried about fire hazard.  The code 
does say it is up to the local jurisdiction...
*****


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                     ~ Windstream Solar ~
     Gary Higbee  (gary at windstreamsolar.com)
                     (541 ) 607-1818 (Eugene)
                        (541) 954-3881 (Cell)
Solar, wind, and hydro site analysis and system design
    Components dealer and installation assistance
 Energy Trust of Oregon contracted system inspector
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 

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