Carflex revisited [RE-wrenches]

Bill Brooks billbrooks7 at earthlink.net
Mon May 28 22:38:21 PDT 2001


Allan,

Some could call it a damp location, but the question is how does that help
us? Most conduit or wire is either rated wet or dry, not damp.

I think most people consider damp areas those that cannot see water from
rainfall so it may be unnecessary to use rainproof boxes and such. I think
our environment of the back of a PV module is much more harsh than under a
canopy--unless, of course, the PV modules were used as part of an actual
roofing system.

Bill.


-----Original Message-----
From: Allan Sindelar, Positive Energy, Inc.
[mailto:allan at positiveenergysolar.com]
Sent: Monday, May 28, 2001 8:22 PM
To: RE-wrenches at topica.com
Subject: Re: Carflex revisited [RE-wrenches]


Bill,
Is it possible that the junction box area on the back of an array could be
considered a damp location: "Partially protected locations under canopies,
marquees, roofed open porches, and like locations", as the description
applies pretty well. It's not "exposed to weather and unprotected", as a wet
location is defined. Perhaps this could provide a solution.
Allan at Positive E

----- Original Message -----
From: "Bill Brooks" <billbrooks7 at earthlink.net>
> I know you two have a history on this subject but the issue is not what
one
> person thinks, but what the code says and how it is generally interpreted
by
> the thousands of jurisdictions across the U.S. The code specifically says
> that any electrical equipment that is in "locations exposed to weather and
> unprotected" is a Wet Location.
>
> 1999 NEC Article 100 (direct quote)
>
> Location.
>
> Damp Location. Partially protected locations under canopies,
> marquees, roofed open porches, and like locations,
> and interior locations subject to moderate degrees of moisture,
> such as some basements, some barns, and some cold-storage
> warehouses.
>
> Dry Location. A location not normally subject to dampness
> or wetness. A location classified as dry may be temporarily
> subject to dampness or wetness, as in the case of a
> building under construction.
>
> Wet Location. Installations underground or in concrete
> slabs or masonry in direct contact with the earth, and locations
> subject to saturation with water or other liquids, such
> as vehicle washing areas, and locations exposed to weather
> and unprotected.
>
> This means that our PV systems are in a wet location unless we have them
> stored in our basement or garage. Now the question comes "what temperature
> rating do I use?" Wire is often rated with multiple ratings. Why is that?
> Because each rating applies to a different application of the product.
Many
> electricians are often confused when the most common wire we use has the
> ratings THHN(90C Dry) or THWN(75C Wet). Does this mean we get to pick
which
> rating we like best? No it means that when applied in a "Dry Location" as
> specified in Article 100 above, that it carries a 90C rating and when it
is
> applied in a "Wet Location" as specified in Article 100 above, that it
> carries a 75C rating. This is stuff that is taught early in apprenticeship
> training programs, but is often forgotten by indoor electricians since
they
> rarely work outside. Every competent specialty electrical inspector that I
> have talked with sees it this way.
>
> I have opened several module junction boxes that were full of water as
were
> their conduits. In open racks like most off-grid applications, it would be
> rare for a water-filled conduit to get over 60C except on days when it
goes
> over 100F (however-using evaporative cooling as a reason for keeping
> temperature down is weak--these are sealed systems with 100% humidity--no
> evaporative cooling). Real temperature measurements on my own, open-rack,
PV
> system show junction box/conduit temperatures of 65C. On top of roofs, the
> temperatures average another 10C hotter. Operating temperatures can reach
> 75C (measured in the field at places like PVUSA) so our "Wet Location"
> rating must be at least 75C for rooftop installations.
>
> "Solar modules are passively heated by the sun, and do not actively
generate
> heat like a compressor."
>
> In the case of a solar module, this passive heating you speak about is
> incredibly intense. It has everything to do with the physics of
> radiation--something called absorptivity. The temperature on a conduit in
> direct sunlight will be less than that conduit connected to a hot solar
> module because the absorptivity of the module is significantly higher than
> that of the conduit. The compressor example you use is often well removed
> from where the conduit entrance is on an air conditioner, so the
temperature
> of the compressor is not translated to the conduit as it is with a solar
> module. If you are connecting a conduit directly to something that is
hotter
> than 60C outside, NMFC rated at 60C will not cut it (remember the rating
> applies to location).
>
> To address the common sense part of the code. We can always come up with
> situations where the code requirements don't necessarily hold in the real
> world. An electrical engineer can, in their engineering judgement show how
a
> PV array will stay under a certain voltage or temperature or whatever they
> can prove analytically to themselves, and then apply their PE stamp to
show
> their confidence in the results (they can still be wrong, but unless
> something bad happens, they won't get caught). The local jurisdiction will
> accept this PE's stamp since it in essence gets the jurisdiction off the
> hook from a liability standpoint in not enforcing the letter of the law.
> With the absence of this engineering judgement, the code provides simple,
> often worst case scenarios, so that every electrical installation does not
> have to go to a professional engineer.
>
> If you don't like the code, think about the cost of going to a
professional
> engineer every time you want to install a PV system. If you think I'm
crazy,
> the Pittsburg, CA jurisdiction had this requirement for a while about a
year
> ago. It took education on what article 690 said for them to relent. Other
> jurisdictions have applied similar requirements until they better
understood
> the PV portion of the code.
>
> As long as our discussions are moving us in the direction of a better
> understanding of how to install code-compliant systems and deal with the
> real difficulties of fielded installations, I'm fine. But to call standard
> code interpretations the "strictest" or accusing people of being code
> fundementalists is counterproductive.
>
> My primary focus is to get inspectors in California comfortable with PV
> system installations, and that the products and engineering that goes into
> those products is fully compliant with the code. When we run into an
> inspector that is particularly difficult, we don't have to make excuses
for
> why we are asking for an exception to the rule, but we can show how it
> complies.
>
> Let's here from the wrenches that work with inspectors every day. It is a
> totally different world when you have inspectors that are inspecting
50-100
> PV systems instead of 1 or 2.
>
> I don't want to establish an US-THEM mentality. Drake and Bob-O, you are
> major players in this industry, and you have a lot of great field
> experience. We may not agree on every issue, but I will never attack you
and
> I hope you choose never to attack me. WE ARE ON THE SAME TEAM. We have
> enough problems with the folks that are our real enemies--as you will see
in
> a post I will make in the near future.
>
> Bill Brooks, PE
>
> -----Original Message-----
> From: Drake Chamberlin - Electrical Energy
> [mailto:solar at eagle-access.net]
> Sent: Friday, May 25, 2001 10:28 AM
> To: RE-wrenches at topica.com
> Subject: RE: Carflex revisited [RE-wrenches]
>
>
> Bill and Wrenches,
>
> The physics of evaporative cooling are well known.  If a conduit is full
of
> water,  and conditions are hot enough to raise the temperature to 60
> degrees C, the water will evaporate quickly. This evaporation will cool
the
> conduit.  When there is no more water in the conduit to cool it, it will
be
> dry, by definition.
>
> 60 degrees C is 140 degrees F.  Try to get into a hot tub at 115
> degrees.  It will turn your skin bright red.  A 140 degree conduit would
be
> quite hot to the touch.
>
> To say conduit needs an 80 degree C rating stretches the credibility a bit
> far.  That is 176 degrees F, hot enough to boil water at high
> altitudes.  Getting these temperatures would require the use of
> concentrators.
>
> Conduits for solar modules are either shaded by the array, or in the
> sun.  Solar modules are passively heated by the sun, and do not actively
> generate heat like a compressor.
>
> If conduits for arrays do get over their rated temperatures, so do
conduits
> for air conditioning units and other compressors.  PV needs to be on a
> level playing field with other types of wiring.
>
> Drake
>
> Bill, etal.
> To me, it boils down to common sense. I KNOW the standard party line
> of those wanting to make PV as expensive as possible by holding it to
> a higher standard than other wiring is that the 80C/60C rating of
> Carflex (and all the others, not to pick one one manufacturer) is
> that if the conduit is used in a wet location it has to rate out at
> the lower number EVEN under dry conditions. I ask you, does that make
> any logical sense at ALL? No. If it's dry, it's dry. If it's wet,
> it's wet. If it is warmer than 60C while wet, it's being used in a
> steam room and is not suitable. If hotter than 80C while dry-again
> not suitable. These are not the usually conditions found in the shade
> behind a PV module.
> Do you REALLY think the spirit of the NEC meant anything different
> that that? I don't think so and any inspectors who do think so have
> VERY likely been influenced by the Code Fundamentalists who believe
> (and publish) that the strictest interpretation of the WORD of the
> NEC, not the spirit and meaning of the good book, is paramount. I
> refuse to believe that the NFPA is that ignorant.
> Bob-O
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