Carflex revisited [RE-wrenches]

Tue May 29 05:44:29 PDT 2001

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Hi Bill,

I regret that you feel attacked by what I have to say.  My approach is 
always to confront the subject, not personalities.  Even views that may 
ultimately prove to be incorrect can be of value in stimulating 
discussions.  The goal is to find the right answers.

As far as temperature conditions affecting flex conduits go, we will need 
to produce "quantitative," well documented test results to prove what we 
know from field experience.  Temperature measurements need to be taken on 
conduits connected to PV modules, compressors, generators and other outdoor 
equipment.

Currently, those of us who work in the PV industry have "qualitative" 
information about temperature conditions.  We know that on a 100 degree F 
day, that it is more pleasant to wire the junction boxes in the shade, on 
the back of a solar module, than it is to run pipe in the sun.  We know 
that we won't burn our hands on the back of a module.  It may be warm to 
the touch, but it will not be boiling hot.  We understand that there are 
many conditions where wiring gets hotter than behind PV modules.

The conduits on the back of a module are connected to the frame, not 
directly to the back surface.  There is air circulation that keeps the 
conduit cooler than the module.  If junction boxes are popping off the 
backs of modules, it is the module construction that is at fault, not the 
temperature rating of the conduit.

I'd like to comment on your following statement.

"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."

I don't personally know of any electricians that work only indoors.   We 
routinely install electrical meters and services, outdoor lighting and 
outlets, yard lighting, air conditioning units and other equipment that is 
exposed to rain and snow. These are fully inspected systems.

Also I'd like to comment on your belief that there is no evaporative 
cooling in conduits.

"...these are sealed systems with 100% humidity--no
evaporative cooling)."

If liquid water can get in, water vapor can get out.  In the real world, 
conduits filled with water will not reach extremely high temperatures.

Also:

"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."

This depends a lot on the installation.  The conduit may well cross areas 
where heat is released.

"If you don't like the code....."

It is not a matter of us liking the code or not.  As electricians, we work 
with the code all the time.  I personally like to have enforced quality 
standards so that I can perform quality work without having to bid against 
sub standard installations.

The  portion of the code dealing with renewable energy has not taken into 
account the cumulative experience of RE workers.  This is an evolving 
portion of the code, and we would like to have input.  We want to be 
certain that requirements address real issues.  We want requirements for RE 
to be equivalent to requirements for all other types of wiring.

The code is extremely subject to interpretation.  The NEC recognizes this, 
in that the "authority having jurisdiction" is responsible for the 
interpretation of the code.  What the local interpretations of the code are 
can have as much impact on the methods of installation in an area as the 
wording.

Thank you for your participation in this discussion.

Drake

At 05:14 PM 05/28/2001 -0700, you wrote:
>Drake and Bob-O,
>
>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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