Utility services can be very dangerous. We live with
all kinds of hazards every day that may be more of a concern than ground faults
on PV arrays. Nobody said that life was fair. The power industry is
far from fair--just look at what is going on in California. Remember, however,
that we are talking about NEC code requirements not big bad utility-imposed
requirements.
I
would like to know what code requirement currently defy logic--I'm sure they're
out there and I know of a few--but ground fault protection is probably not one
of them. I have made several cases for why I think it does make sense and have
not heard a rebuttal to my examples yet.
Logic
says that if you have a ground fault in your array or array wiring, the system
should shut down until someone fixes it. This is clearly a product warranty (if
the module is at fault) or installation problem (if the installer is at fault).
What is more logical to me is to make ground fault protection a requirement for
all systems 48 volts and above--regardless of roof mounting or not. The only
logic that escapes me is why the 1984 authors of article 690 limited this
requirement to roofs of dwellings when it is clearly more than just a wood
structure fire hazard issue. We know this now much better after 20 years of
experience with higher voltage systems.
Remembering back to the early 1980's in grid-connected
PV research, the big emphasis was building integrated products similar to the
Atlantis SunSlate product. All of these products failed miserably for various
reasons and had lots of ground-fault problems. These system were mounted
directly on the wooden roofs and exhibited a variety of ingenious ground fault
paths. My guess is that 1984 authors of article 690 had these problems in their
minds when they drafted this requirement thinking that the majority of the
systems in the future would be roof integrated. I will have to ask a few
old-timers that worked at the Southwest Technology Development Institute if I am
on the right track.
Bill
Brooks
In a message dated 02/20/2001 7:18:08 PM
Pacific Standard Time, jay@asis.com
writes:
> I also doubt that a roof mounted array is as dangerous as a
240 volt
> service drop coming from a pole, capable of delivering
10,000 amps. There
> seems to be a tendency to require RE
installations to be 10 times safer
> than grid connected systems.
Why is that?
Drake, a very good question. I too
think that we are burdened with some dumb
code requirements that
basically defy logic.
Best, Don - - - - - - -
- - - - - - -
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