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<font size=3>Kent:<br><br>
Your comments below are right on the mark and well said.<br><br>
William Miller<br><br>
<br><br>
<br><br>
At 09:43 PM 9/7/2010, you wrote:<br>
<blockquote type=cite class=cite cite>Matt,<br><br>
There is a word on the KLKD time delay chart you referenced that is
hiding a very important fact. Those are "average"
curves. To illustrate what that means take a look at the time delay
curve for the
<a href="http://www.cbi-electric.com/show_pictures.php?title=Product%20Curves&path=/curves_products/6">CBI
breaker</a> commonly used for battery charging systems. There is a
gray area that extends from 105% to 130% of rating. Over that
range, the breaker may or may not trip. While not shown on the KLKD
fuse time delay chart that you referenced, a very similar gray zone
exists. These fuses and breakers are simply not precise enough
devices to distinguish between Imp and Isc at STC in the best of
conditions. <br><br>
if you did manage to select a fuse that would blow at Isc but not at Imp,
it still wouldn't blow during a short if the irradiance was 800 W/sq
m. An arcing fault at 800 W/sq m can still burn a big hole.
It simply isn't possible to provide good fault protection for PV systems
with fuses. What's needed is a ground fault protector/arc fault
protector that is located in the combiner box. Until that exists,
the feeder between the combiner and inverter needs to be considered an
unfused conductor.<br><br>
Kent Osterberg<br>
Blue Mountain Solar<br><br>
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