Jeff
EMT is fine on the roof. Rigid will add weight to the roof, as well as increase
your labor costs to install it.
My take away from the Target project after reading the report was they did not
use the correct fittings. Coupled with long conduit runs and perhaps not using
junction boxes and providing loops in the box to address expansion and
contraction contributed to the incident. It is like a plane crash- it is
usually not one thing that makes the plane crash, but a series of events that
leads to the demise of a situation. It seems the same goes for the Target
project.
If any of you have ever driven over a bridge and have sat in traffic, sometimes
you get visually exposed to the conduit runs, and the expansion fittings. You
will also see junction boxes, with generous loops of wire to address the
expansion and contraction that occurs.
Also, the temp derate on 310-15-B-2-C has a table for exposed conduits on the
roof; 310-16 & 310-17 should be reviewed.
Keith
________________________________
From: Jeff Yago <[email protected]>
To: RE-wrenches <[email protected]>
Sent: Sat, December 5, 2009 8:03:04 AM
Subject: Re: [RE-wrenches] large array conduit runs
We are starting to get much larger grid tie systems above 100 kW and I still
remember very clearly that Target melt down related to conduit that shorted out
a bundle of string runs between the array and inverters due to improper
allowance for expansion and contraction in the long above roof conduit runs.
With this in mind I wanted to specify a conduit between multiple array rows
back to the inverters and we get rain, snow, high temps, low temps that make me
want to go with extra protection and cable support and have budget to do it
right.
What type of metal conduit are you using on these larger roof array commercial
systems - - - EMT, Intermediate, pipe, other?
Thanks,
Jeff Yago
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