[RE-wrenches] Cable tray

[billbrooks7 at sbcglobal.net]

Brian,

 

I don’t know that I have a lot of good news for you. I have looked into this and I really don’t see a good way out of making some pretty conservative assumptions. You can read what I wrote in my IAEI article on Support of Exposed Cable earlier this year. I get into ampacity briefly though it is not the focus of the article.

 

http://iaeimagazine.org/magazine/2015/04/14/support-of-exposed-cable-for-pv-systems-requirements-and-recommendations/ 

 

Bundling 50-60 conductor together should have a much worse impact than working off the free-air table. I believe the only way to evaluate that bundle is to treat it as if it is in a raceway.

 

The lesser number of conductors (bundle of 3 or 4), the more it will begin to act like a free air cable.

 

Bill.

 

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Brian Mehalic
Sent: Monday, August 31, 2015 2:56 PM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: [RE-wrenches] Cable tray

 

Hello wrenches, question about running conductors in cable tray.  So we have our allowance in 690.31(C)(2) for using small PV Wire in cable tray for PV source and output circuits.  I'm trying to determine what adjustment factor to apply when there are a bunch of small conductors.

 

392.80(A)(2)(a) and (b) both address single conductor cable in covered cable tray, but only refer to conductors from 1/0 to 500 kcmil, and 600 kcmil and up.  I'm looking more at 40 or 50 12 AWG conductors (20 to 30 source circuits).  The adjustment factors in 392.80(A)(2) are pretty hefty - only 60 to 70% of the rated ampacity, but as stated in Table 301.15(B)(17) (conductors in free air, so that helps). 

 

Any guidance would be much appreciated, and thanks for your time,


 

Brian Mehalic 
NABCEP Certified Solar PV Installation Professional™ R031508-59

 

PV Curriculum Developer and Instructor

Solar Energy International
http://www.solarenergy.org



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