DC Runs in the Attic [RE-wrenches]

[Barbra Kerr]

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Mark -  

This is now a common requirement in the City and County of San Diego.  I
have met personally with the head of both building departments and their
explanation is this:

Concern for future work by unaware personnel.  The City will allow us to run
DC conduit ONLY 10 feet through the attic space.  They have allowed us to
place the DC disconnect on the roof (i.e. mounting platform or against a
very large chimney), and THEN run as much DC conduit through the attic we
like.  The County on the other hand will allow any amount of DC conduit in
the attic or walls as long as we label it "Photovoltaics - High Voltage DC".
We spray the conduit yellow and label it every 5 feet with black sharpie.
For both jurisdictions, we are required to provide a red site map sign
(plastic) at the AC disconnect indicating location of ALL components.  The
AC disconnect is also labeled as 1 of 2 disconnects, the DC 2 of 2
disconnects.  With all this labeling - anyone that would miss it shouldn't
be on the site!

regards...


Barbra K. Kerr
Kerr Enterprises, Inc

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


 

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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.  We have tried to convince him
with the following points:  1) Unlike power from the utility, a PV array is
inherently current limited.  The short circuit current, even with 25%
derating per 690.8(A)(1), is much less than half the wire's ampacity at 90C.
2) We use metallic conduit with no J-boxes or splices in the run.  The wire
is continuous and therefore very unlikely to fail or overheat, plus it is in
metallic conduit - double protection.  3) The utility already runs the
service entrance wire through the residence (although a shorter distance) if
the service entrance panel is flush mounted (of course, this is in rigid
conduit).  4) PV installations will be much less aesthetic with EMT on the
roof and exterior walls.

We even got John Wiles involved to talk to him, but so far no dice.  I plan
to elevate it to the building official but I thought I would ask you all -
do you run the DC through the attic?  Do your local jurisdictions allow
this?  Do you have any other good arguments to help convince him?  By the
way, DC runs through the residence will likely be explicitly allowed in the
2005 code.

Thanks
Mark
Cobalt Power Systems

[Non-text portions of this message have been removed]

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