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

Tue Aug 25 09:21:34 PDT 2009

Hans,

The 2002 NEC 352.12D states that RNMC can't be used where ambient temps
exceed 50C unless listed otherwise.  Most of the PVC we see is listed
otherwise, max 90C right on the conduit.

Jeff 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Hans
Frederickson
Sent: Monday, August 24, 2009 6:33 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] Thermal issues with PVC (was RE: raintite
boxmounting angle)

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

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