Not sure about the rest but under ground conductors are considered a wet location.
Jesse Dahl NABCEP PV Installation Professional IBEW Local 292 - Electrician Electrical/Solar PV Instructor - HCC Sent from my iPhone > On Jun 23, 2016, at 3:41 PM, Peter Parrish <peter.parr...@calsolareng.com> > wrote: > > I am working with a customer who is doing a complete remodel, and upgrading > to PV and Smart Energy Storage. The house was broken down to floor joists, > open studded walls and open roof rafters. > > The client wanted a 8 kW/16 kWh Smart Energy Storage system and a 10 kW-ac PV > system. The Main panel, the Critical Load sub-panel, the Energy Storage > system and the PV inverters will all be either in a detached garage or hung > on the west facing exterior wall of the detached garage. > > We have been given a number of 1-1/2” PVC conduits, buried a minimum of 18”, > that run between the main house and the detached garage, so we have to convey > 2/3rds of the PV source circuits and all of the critical load branch circuits > using this conduit. This raises a number of questions/confirmations: > > (1) We cannot mix PV source circuits and critical load branch circuits in > the same conduit. Pretty obvious. > > (2) What ambient temperature should I use in my ampacity calculations? I > assumed something less than 30°C, such as 20°C. But I read somewhere that one > has to be careful when the conduit exists the ground, in that one has only > 18” of conduit above ground before one has to use the full maximum ambient > temperature which in our case is 45°. The argument says that for the first > 18”, the portion of the copper conductors in the ground will cool the portion > of the conductors above ground via thermal conduction. I can’t find any > citation to confirm this argument. Does anyone have any sources of > information on the subject? Even if there is a sound engineering basis for > the argument, soon after exiting the ground, one would need a vault to splice > in a higher ampacity conductors and continue on to either the critical load > sub-panel or the inverters, you have to calculate the ampacity at 45°C. These > buried conduit runs are approximately 50 feet in length. > > (3) One end of the conduit run is supposed to come out of the ground > inside the building envelope, so we could derate using 30°C or so for air > conditioned space. We cannot count on the garage being air conditioned > however. > > (4) Can we use THHN as opposed to THWN-2? I am assuming the forces of > nature or human stupidity will eventually cause the PVC to crack and the > extra expense of THWN-2 (or another wet rated 90°C conductor) will be a > better choice. > > This job is the same one where the electrician claimed that neutrals on a > 120V branch circuit don’t count as current carry conductors in conduit for > the purposes of de-rating ampacity. He’s gone, but his replacement may not be > any more careful in his ampacity calculations. > > Faithfully yours, > > Peter T. Parrish, Ph.D. > NABCEP™ Solar Professional #031806-26 > President, SolarGnosis > 1107 Fair Oaks Ave. > Suite 351 > South Pasadena, CA 91030 > (323) 839-6108 > peter...@pobox.com > > _______________________________________________ > List sponsored by Redwood Alliance > > List Address: RE-wrenches@lists.re-wrenches.org > > Change listserver email address & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://www.mail-archive.com/re-wrenches@lists.re-wrenches.org/maillist.html > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out or update participant bios: > www.members.re-wrenches.org >
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