[RE-wrenches] PV Wiring methods

Bill Brooks billbrooks7 at yahoo.com
Thu Nov 14 16:27:33 PST 2013


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: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] 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: re-wrenches-bounces at lists.re-wrenches.org
<mailto:re-wrenches-bounces at lists.re-wrenches.org>
[mailto:re-wrenches-bounces at lists.re-wrenches.org] 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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