[RE-wrenches] Thermal issues with PVC (was RE: raintite box mounting angle)

Mon Aug 24 15:33:22 PDT 2009

Picking up on Max's comment about PVC conduit coming apart in the heat...
PVC is acceptable for use above ground, but is often not a good choice in
exposed outdoor areas due to thermal issues:

First, PVC conduit is not permitted to be used where ambient temperatures
exceed 50 degrees C (122 degrees F) per NEC 352.12(D). This limitation rules
out using PVC on most roofs, although you will occasionally see it used on
"cool" roofs in our neck of the woods (pacific NW). It follows that PVC
junction boxes would not typically be a good idea on a hot roof unless they
are specifically listed for higher temperatures.

Second, PVC of any significant length installed outdoors generally will
require an expansion fitting. See NEC 352.44 for details. The rule of thumb
we use around here is any piece of PVC conduit longer than 10' installed on
an exterior wall needs an expansion fitting. If you find yourself needing to
install an expansion fitting, this document from Carlon is very helpful:

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Max
Balchowsky
Sent: Monday, August 24, 2009 2:28 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] raintite box mounting angle

We use a high voltage coating to water proof splices, whether they be wire
nuts (which I don't like to use on DC circuits) or the plastic coated
terminal strips, which I prefer. That's left over from my days as a traffic
signal technician and splicing loop detectors in below grade pull boxes,
which, more often than not, fill with water in the rain. Joel, I used the
metal boxes (with the weep hole ) in the desert, but here on the coast the
plastic boxes seem to work fine, and I've had some installs that are 10
years old (back to the beginning of the ladwp program). What I saw to be a
problem in the heat was the jobs I was called in to fix (other contractor's
installs) where they used the plastic PVC conduit on the roof - always came
loose in the heat. It's designed for underground, not surface work.

Max Balchowsky
SEE Systems
760-403-6810

________________________________

From: Joel Davidson <joel.davidson at sbcglobal.net>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Monday, August 24, 2009 1:25:36 PM
Subject: Re: [RE-wrenches] raintite box mounting angle

I always drill a 3/16-inch weep hole in boxes that could fill up with water.
Even properly vertically mounted boxes can get water in them. In Sacramento,
I had some metal conduit homerun from the roof and then down a 25 ft north
wall. The conduit was like condensing tubes that dripped water into the DC
disconnect boxes at the bottom of the vertical conduit runs.

Joel Davidson

________________________________

From: Peter Parrish <peter.parrish at calsolareng.com>
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Monday, August 24, 2009 1:11:49 PM
Subject: [RE-wrenches] raintite box mounting angle

Max,

A cautionary tale. We used those puppies for a while until we had a call
back from a customer with a ground fault / off line condition. We found that
the box had warped, the seal rendered ineffective and the splices sitting in
0. 5" of water. After thinking about it, we decided that the 140+ deg F
summer roof temperatures probably caused the plastic to warp under thermal
stress. They probably would work just fine off the roof, but I can't
personally vouch for them.

- Peter

Peter T. Parrish, Ph.D., President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com  
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885

________________________________

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Max
Balchowsky
Sent: Monday, August 24, 2009 12:48 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] raintite box mounting angle

We've been using the 6x6x4 plastic boxes with a gasket (electrical section
of most home depot stores)- mount them on their side at the edge of the
array. They are rated for electrical wiring and are water proof and have
been accepted and passed by every electrical inspector we've had over the
last few years. They are used alot by landscape contractors for j-boxes in
the ground.

Max Balchowsky
SEE Systems
760-403-6810

________________________________

From: Bill Brooks <billbrooks7 at yahoo.com>
To: kirk at vtsolar.com; RE-wrenches <re-wrenches at lists.re-wrenches.org>
Sent: Monday, August 24, 2009 9:08:34 AM
Subject: Re: [RE-wrenches] raintite box mounting angle

Kirk,

I'm fairly confident that if the manufacturer does not specify an angle for
NEMA 3R (rainproof) that the default is vertical. In special cases (e.g.
Outback PSPV), the NEMA 3R tests are requested at an angle, but this is
fairly rare. Upshot is that NEMA 3R boxes normally cannot be mounted in the
plane of the roof, while NEMA 4 and up can be mounted in the roof plane
since many of these boxes can be mounted from vertical to horizontal.

Bill.

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Kirk
Herander, VSE
Sent: Monday, August 24, 2009 8:26 AM
To: 'RE-wrenches'
Subject: [RE-wrenches] raintite box mounting angle

Hello,

Can anyone give a recommendation for a minimum mounting angle of a raintite
box? Ideally 90 degrees, but in this case I may be forced to mount it at the
same angle as the panels - about 25 degrees, mounted off the roof about 6
inches. I don't think there is any reference in the NEC to this. It will be
off the roof about 6 inches in a mild climate, where they only get about 20
inches of snow a year. Thanks.

Kirk Herander

Vermont Solar Engineering

802.863.1202

NABCEP(tm) Certified Solar Installer

NYSERDA-eligible Installer

VT Solar Incentive Program Partner