<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Since the topic of AFI's has come up I wonder if anyone has actually tested one, even an AC one.<div><br></div><div>From what I've read from some tests on the Mike Holt site for AC breakers is that they couldn't get them to work at anything less than standard ISC for the breaker.</div><div><br></div><div>thanks,</div><div><br></div><div>jay</div><div><br></div><div>peltz power</div><div><br></div><div><br></div><div><div><div>On Apr 4, 2010, at 10:47 PM, Kent Osterberg wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
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Ray,<br>
<br>
The exception in 690.8(B)(1) reads: Circuits containing an assembly,
together with its overcurrent device(s), that is listed for continuous
operation at 100% of its rating shall be permitted to be utilized at
100% of it rating. The field installed cable used to connect a
breaker is not part of an "assembly that is listed for continuous
operation at 100% of its rating" and as such the cable still has to be
sized to carry 156% of Isc.<br>
<br>
I agree with you about the need for DC arc fault protection. I believe
the 2011 code is going to require it for circuits over 80 volts. But
it seems unlikely that such a device will exist for a while. It will
have to have embedded electronics for detection that operates the
contacts. And at present we resort to 600 volt fuses because "simple"
breakers rated for 600 volts dc are excessively expensive. When dc
AFCIs are available, they are sure to be expensive and are likely to
add $100s to the cost of a combiner box.<br>
<br>
Kent Osterberg<br>
Blue Mountain Solar, Inc.<br>
<br>
<br>
<br>
R Ray Walters wrote:
<blockquote cite="mid:5FE1A816-7D91-42D2-8A1F-900D49055C41@solarray.com" type="cite">And just to be clear, when using these 100% duty rated
breakers, you only have to oversize the cable by 125%, not 156%.
<div><br>
</div>
<div>Also, as William mentioned, even correctly sized wiring can have
problems; we just recently had a short circuit that caused quite some
damage in a junction box, and the breaker never tripped.</div>
<div>The 156% rule has its downsides too, as you end up with a
breaker so oversized that array current will never trip it, even if you
wish it could.</div>
<div>I'm now advocating for DC Arc Fault protection, as I have seen
several cases of dangerous DC arcs that sustained for several minutes,
but never drew enough current to trip a breaker.( but did create heat
over 2000 degree F )</div>
<div>The standard thinking for safety in electrical systems assumes
an infinite current supply that will trip a breaker, as soon as
something goes wrong. (true for grid power, and battery systems) But on
the PV source circuit, many bad things can happen that will not be
stopped by the breakers. Also, high voltage DC has much more Arc
potential than AC, so AFI protection is even more important.</div>
<div>Now, we just need somebody to make a reasonably priced UL listed
DC AFI unit.</div>
<div><br>
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<div>R. Walters</div>
<div><a moz-do-not-send="true" href="mailto:ray@solarray.com">ray@solarray.com</a></div>
<div>Solar Engineer</div>
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