[RE-wrenches] large array conduit runs

[Keith Cronin]

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 <jryago at netscape.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
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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