Carflex revisited [RE-wrenches]
Bill Brooks
billbrooks7 at earthlink.net
Mon May 28 23:03:41 PDT 2001
Bob,
It is buried in two or three of my posts. I believe the most acceptable
method is USE-2 cable with cable glands to enter the junction boxes. Tray
cable with THWN-2 wire is equally good, but since it is not expressly
mentioned in article 690, some inspectors question it.
Bill.
-----Original Message-----
From: Bob Ellison, Alternative Energy Systems [mailto:ellison at gisco.net]
Sent: Monday, May 28, 2001 5:20 PM
To: RE-wrenches at topica.com
Subject: RE: Carflex revisited [RE-wrenches]
OK Bill, So what is your suggestion for a "legal" way of doing the wiring on
a rack of panels?
Bob
RE. Ellison
Supplier of;
Diesel Generators &
Alternative Energy Systems & Supplies
34642 Countryman Road
Theresa, NY. USA
13691-2076
-----Original Message-----
From: Bill Brooks [mailto:billbrooks7 at earthlink.net]
Sent: Monday, May 28, 2001 8:14 PM
To: RE-wrenches at topica.com
Subject: RE: Carflex revisited [RE-wrenches]
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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