DC Runs in the Attic [RE-wrenches]

Sun Sep 19 06:49:44 PDT 2004

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Gary,

I can speak to one item. In commercial buildings, disconnect switches
for mechanical equipment are allowed on a roof. Some of these roofs have
pretty lousy access, ladders and hatches. (Forget the disconnect, try
hauling filters for maintenance up a hatch, or a replacement motor!) I
think this is also true for houses. Think of furnaces in attics (another
bad idea, but common practice in some areas.) Here, the ladder is not
even permanent usually.

So I think a more usual interpretation of the code is that a disconnect
needs to be accessible once you're in that space near the equipment in
question, but the space does not need to be as easily accessible. I know
that not all AHJ view this the same way.

Now, I'm not disagreeing with your desire to not have DC disconnects on
roof. Our response to this issue is that we use it as a tool to get the
homeowner to always agree to a nice straight conduit run down the side
of the house, outside the attic. Looks good, and if you stare at the
side of most houses, there are all kinds of things cluttering it up.
(Electric service, cable, telephone service, satellite, two satellites,
etc.) We've not found that folks have a problem with this, even in the
"high rent districts".

I'm not for adding DC arc fault breakers. My understanding is that the
AC arc faults do not do anything that a normal breaker does not do. (I
know they are designed to do more, but the last I heard, some
electricians, maybe wrenches, who did some "real world" testing could
not make them trip on a low level fault, which is there purpose.) So
just more money, more connections, and more maintenance.

Jeff Wolfe
Global Resource Options

-----Original Message-----
From: Gary Higbee [mailto:gary at windstreamsolar.com] 
Sent: Sunday, September 19, 2004 3:20 AM
To: RE-wrenches at topica.com
Subject: Re: DC Runs in the Attic [RE-wrenches]

 -------------------------------------------------------------------

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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