I definitely think cable tray is a good compromise between conduit and
loose zip tie wiring; I primarily question rodent protection.
Even cable trays can go horribly wrong: I've seen them not supported
properly and bend or even fall over spilling cables onto the roof or ground.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 11/14/2013 5:27 PM, Bill Brooks wrote:
William,
I know your long-time stance on conduit. It has its place. This report
was about an integrated PV system that caught fire because of a module
failure---this was not a cable management issue. We can all jump on
our respective soap boxes and pontificate---I have no problem with that.
I don't think you are correct on either reason for "lax wire standards".
1.When 12- and 24-V systems were done, they were all in conduit until
post 2000 when cable and connector systems began to be used. Not the
reason for lax standards.
2.Cable management is not more lax in Europe. You typical German
electrician (far more competent than your average American
electrician), works with exterior cabling systems all the time in ac
wiring. They do beautiful work in general---there are always
exceptions to every generalization, but we have a lot to learn from them.
Lastly---conduit systems on large rooftop PV systems have proven to be
very problematic to the point where I would not recommend the use of
metallic conduit on feeders longer than 200-feet. Everything should be
in cable tray.
Down off my soapbox---with all respect in the world to you. Hop up
again if you please.
Bill.
*From:* [email protected]
[mailto:[email protected]] *On Behalf Of
*William Miller
*Sent:* Wednesday, November 13, 2013 1:42 PM
*To:* 'RE-wrenches'
*Subject:* [RE-wrenches] PV Wiring methods
Bill:
I respectfully disagree with your logic: Define "perfectly
installed." If your connections are tight and permanent and the
conductors are protected from damage, you have a great chance of a
reliable, safe lifetime of service. How can you guarantee that your
leads will stay protected after the ties fail? Studies show that even
UV resistant wire ties will fail well before the life expectancy of
the system has expired. When the ties fail, your PV leads are hanging
on the roof. Even before the ties fail, rodents can chew on them.
Conduit was invented for a reason and we should be using it.
I agree that arc-fault breakers will improve the situation, but I
don't think any form of OCPD is a substitute for good wiring
practices. I think wire protection is just as important on PV
circuits as it is on any other high voltage circuit. Try getting away
with wiring a rooftop air conditioning unit by tying the conductors to
some metal framework with plastic ties and see how long it takes to
get red-tagged by your local inspector.
I suspect we've gotten to where we are on lax wire protection
standards for two reasons:
1.In the early days, PV was low voltage, 12 to 24 volts, and was
treated as such, even though current capabilities exceeded that of
conventional low voltage thermostat, door-bell and telephone wiring.
2.It is my understanding that PV wiring standards in Europe are not
stringent, and European demand drove the PV market for many years.
Products were built to satisfy the European market and US standards
had to work with the equipment available.
Some would say: "if it is under the array, it is protected." We have
seen PV wire getting damaged under arrays and it is possible to get
damaged under BPIV components as well. I believe that protecting PV
wire is more important than protecting conventional AC circuit wiring
because PV circuits are more prone to create and sustain arcing.
Some say that protecting PV wire in conduits will add too much expense
to PV installations. Consider the cost of fires and, inevitably,
injuries and deaths. One news story about an obscure, rarely used
product is already causing many of us headaches. Statistically, it is
inevitable that more accidents will happen. I don't want that on my
conscience.
I would suggest that we need to expand the discussion beyond fire
hazards. I also worry about electrocution hazards in high voltage PV
circuits. Good wire protection is essential in preventing contact with
high voltages.
Unprotected PV wiring is an irresponsible practice. I am fighting an
uphill battle to develops methods to protect PV wiring because the
industry is not helping at all. The trend has been to make it harder
to protect wiring. This trend will result in accidents. I think we
should do better.
Sincerely,
William Miller
*From:*[email protected]
<mailto:[email protected]>
[mailto:[email protected]] *On Behalf Of *Bill
Brooks
*Sent:* Monday, November 11, 2013 3:38 PM
*To:* 'RE-wrenches'
*Subject:* Re: [RE-wrenches] RE-wrenches Digest, Vol 6, Issue 423
William and David,
This particular problem goes away with arc fault detection. The longer
we wait to introduce arc fault detection into our systems, the more we
will have opportunities for news reports such as the one William
brings forward. Wire ties are not the problem. Could a wire tie cause
a problem-sure, just like anything improperly installed.
At the end of the day, you can a have a perfectly installed system,
but if it does not have arc fault detection and high resolution ground
fault detection, it can still catch on fire. You have no control over
product failures other than buying from large companies that can
actually insure their products in a failure.
Fires are not that common, but it didn't take much to get all the
viewers of this news report up in arms did it?
Bill.
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