Gray Flex [RE-wrenches]

Sun Apr 22 13:34:13 PDT 2001

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Bill and Wrenches,

Many air conditioners do experience both hot and wet conditions.  Central 
air conditioning units are located outside, with the conduits often in full 
sun.  They carry the most current, for the longest periods of time, exactly 
when it is the hottest.

Air conditioning compressors, as well as compressors for commercial 
refrigeration units are often mounted on flat roofs.  These are often black 
tar roofs that get very hot in the midday sun.

Flexible conduits are mounted to units that pump heat from one space, and 
release it in the unit.  Additional heat is generated by the motors.

Conduits on the back of PV modules are shaded by the module.  PV modules 
are not heat concentrators or collectors.  They produce no mechanical heat.

Requiring conduits to be rated for 80 degrees C wet seems extreme.  If you 
have hot conditions, you will not have wet conditions.  80 degrees C  is 
176 degrees F!

60 degrees C is 140 degrees F.  Water will dry up fast under these 
conditions.  I know of no place on the surface of the planet that will 
generate 140 degree F  temperatures under wet conditions, with the possible 
exception of geothermal zones.

May be with continued global warming we will see these conditions.  If we 
do, we will have more to worry about than damaged conduits.

Drake

At 09:43 PM 04/21/2001 -0700, you wrote:
>Joel and others,
>
>The point is not that air conditioners don't get got and wet, they just
>don't get nearly as hot as the back side of a PV module. For roof mounted
>arrays in warm climates (Los Angeles), it is best to use 75C as the hottest
>ambient temperature (on the back of the module). This means that the conduit
>must be rated for at least 80C (wet since it is outdoors). The conductors we
>use to connect to the module must be at least 90C rated to allow current
>flow (a 75C wire at 75C has zero ampacity by definition). Non-Metallic
>Flexible Conduit is normally 60C wet rated but can be purchased in 80C,
>which is fine to use.
>
>If you are mounting the modules in an open rack like most of our off-grid,
>ground-mount and pole mount systems, the hottest temperature never go above
>about 65C, so 75C wire is okay, but the 0.33 multiplier must be applied to
>the ampacity calculation (e.g. 10 ga. wire has a 16 amp ampacity at these
>temps).
>
>Bill.
>
>-----Original Message-----
>From: Joel Davidson [mailto:joeldavidson at earthlink.net]
>Sent: Saturday, April 21, 2001 10:05 AM
>To: RE-wrenches at topica.com
>Subject: Re: Gray Flex [RE-wrenches]
>
>
>Gray flex on air conditioner installations gets hot and wet. For many years,
>manufacturers, distributors, installers and inspectors have accepted gray
>flex.
>What should be used on air conditioner installations that would be better,
>cheaper and faster than current practices?
>
>Bill Brooks wrote:
>
> > Answer,
> >
> > USE-2 cable or Tray Cable without conduit using cable glands to connect to
> > the junction boxes is cheaper than conduit and more appropriate in many
> > cases. Many modules are not "conduit ready". Just because it has a 3/4"
> > knockout, does not mean you can put a piece of conduit on it. We have many
> > examples of conduit causing junction boxes to pop off the backside of the
> > module. If the installation directions don't mention conduit you CANNOT
>put
> > conduit on them.
> >
> > If you put conduit on a module it must be a minimum of 80C wet-rated. The
> > stuff you buy at HOME DESPOT is 60C rated and can weaken and fall apart at
> > the temperatures we work with. I'm not making this stuff up or just
> > regurgitating John Wiles stuff, I've seen it on several occasions in the
> > field. The crap they often put on A/C units rated for lower temperatures
> > should NEVER be used on PV system.
> >
> > Now that oughta get some reaction--anyone care to take me to task on this
> > one? (in good fun of course)
> >
> > Bill.
> >
> > -----Original Message-----
> > From: Joel Davidson [mailto:joeldavidson at earthlink.net]
> > Sent: Saturday, April 21, 2001 9:17 AM
> > To: RE-wrenches at topica.com
> > Subject: Gray Flex [RE-wrenches]
> >
> > Flexible conduit is used almost always to wire outdoor air conditioners
> > and passes inspection. Yet some designers say do not use gray flex for
> > PV module interconnects and short sub-panel whips. What is better,
> > faster, cheaper than gray flex?
> >
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