Dick:
We are gong to install HU361 disconnects at the PV. Touch-safe fuse holders
are one way to apply disconnecting means rated at 600 VDC to a Sola Deck
device. Fusing at an array and GFDI at an inverter do not de-energize PV
feeders. Combiner fuses, if required, protect only adjacent arrays. They
will not open if a feeder is violated. In my humble opinion, this is one
of the serious, unrecognized hazards of the PV industry.
Burial tape is always a good idea, but it is only effective if the backhoe
is taking shallow scoops. I don't believe it is required so it does not
always get installed. Most of our run is already in the ground without tape.
If a PV array were present, I would hope an operator would be more
cautious, but without surface marking, it is difficult to be cautious over
an unknown distance. If I was digging near an array, I would examine the
perimeter of the array looking for a disconnect and/or a telephone number
for the installer.
Never thought about dumping fill over arcing leads. I'm not sure this is SOP.
Each scenario is different, but I like working on de-energized leads and it
is standard in other electrical trades to require that it be possible to do
so. Without disconnecting means, how is this accomplished? I like
avoiding the expense of disconnecting means as much as anyone else, but I
do want to leave a legacy of safe installs.
Lastly, a 1Kw array at 550 VDC is just as lethal as a 100KW array at 550VDC.
This conundrum is new on my radar and I'm still working this out in my own
mind. It was brought up by a recent post regarding PV feeders through an
adjacent building and also this job with conduit-finding back hoes. I
think the issue is warrants discussion. Thanks for participating. I enjoy
your view point and the camaraderie of this list.
William Miller
At 11:34 AM 12/20/2009, you wrote:
William,
Not sure I understand how buried PV runs protected by touchsafe fuses in
combiner boxes at the array and GFCI protection at the inverters constitute a
fire hazard.
That's not saying I disagree with your disconnect here. I don't. If it was
a 1kW
system, would you still install one? I would not.
Would not a deeper trench with properly located burial tape have been a good
call? If the array was installed and visible, maybe the excavation operator
would have thought to ask about underground utilities.
They should have anyway. Would not common sense imply the operator would
drop a
bucket of fill on any sign of arcing. Would they know to look for a disconnect
at the array in any case?
Common sense can be slippery.
Dick
Solarwind Electric
--- You wrote:
Friends:
I am embarking on a 10 Kw ground mount grid-tie installation. The client
prepared for this installation some time ago by stubbing a PVC conduit
underground towards the future location of the PV array. Prior to
beginning this job, an excavation contractor intercepted the empty conduit
with a backhoe.
No harm was done because this conduit was empty. Had this conduit been
filled with PV feeders, it would have been very necessary to be able to
disconnect the PV arrays, both for safety and to prevent a brush fire in
our very dry climate.
The inverters will be located in a pump house about 130 feet from the PV
arrays. I would not normally put disconnects at the array and they are not
required. This scenario, however, has caused me to reconsider. The design
now calls for a disconnect at each row of modules. I feel that it would
not be prudent to delete this important safety item.
I wish there were a better selection of compact, low profile disconnects
suitable for a roof-top installation. I have put external handle
disconnects on roof but they look terrible. I may specify touch-safe fuse
holders inside of a Sola Deck for future comp roof jobs. I am not sure
what we will do with tile roofs.
It seems to me that every source of power should have a means of
disconnection as close to the source as possible. This is just common sense.
William Miller
_______________________________________________
List sponsored by Home Power magazine
List Address: RE-wrenches@lists.re-wrenches.org
Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out participant bios:
www.members.re-wrenches.org
