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Thanks Robin. I've long been suspicious that the CBI circuit breakers
should not be run at 100% for a couple reasons:<br>
1) I've seen too many 60-amp CBI breakers on charge controllers trip
habitually. But a replacement 60-amp breaker works fine.<br>
2) Nothing in the CBI literature that is available on their web site
says the QY breakers are rated to operate at 100%.<br>
The published trip curve shows that the breaker is supposed to hold at
less than 105% of rating and trip at more than 130% of rating. <br>
The trip curve for a QO breaker shows that it is supposed to hold at
100% of rating and trip at 130% of rating too. Yet we know that it is
not intended for continuous operation at 100% of rating. <br>
<br>
Kent Osterberg<br>
Blue Mountain Solar, Inc.<br>
<br>
<br>
boB Gudgel wrote:
<blockquote cite="mid:4BB7ABD7.9040608@midnitesolar.com" type="cite"><br>
Forwarding a message from Robin Gudgel...
<br>
<br>
Robin Gudgel wrote:
<br>
<blockquote type="cite">The CBI QY series of DC breakers have an arc
shoot that is required to
<br>
quench a DC arc. This breaker would work just fine as an AC breaker
although
<br>
is not marked as such. I am not sure if the AC breakers (QL, QZ and QZD
<br>
series) have the arc shoot. I was told years ago by CBI that the AC and
DC
<br>
breakers are built the same, but I had never broke one open to see if
the
<br>
arc shoot is present on AC breakers until today. The AC breakers do in
fact
<br>
have the same arc shoot as the DC breakers. CBI just marks the outside
of
<br>
the breakers differently. You don't want to get called on the AC vs. DC
<br>
issue by an inspector because you are going to lose that battle. It
makes
<br>
things a bit confusing to have a DC breaker in an AC circuit even
though
<br>
they are identical inside. I believe Allan Sindelar was in the field
and had
<br>
a situation where it saved a bunch of time and hassle to use a QY
breaker
<br>
instead of a QL that he did not have on hand. I had told him that the
DC
<br>
breaker would function just fine as an AC breaker. That installation
was
<br>
safe, but an inspector would probably make you change to an AC breaker.
<br>
<br>
I remember years ago seeing in print that a Hydraulic/Magnetic breaker
could
<br>
be used at 100% duty rating where as a thermal breaker could only be
used at
<br>
80%. I have searched and searched to find this written explanation
again to
<br>
no avail. I thought it was in the NEC, but I now believe I was wrong.
If the
<br>
NEC does not allow the use of H/M breakers to be used at 100% duty
cycle,
<br>
then it just is not allowed. It is true that the H/M breakers are not
<br>
affected by temperature like thermal breakers are, but that in itself
<br>
doesn't overrule the NEC. I personally have been spreading this myth to
<br>
hundreds of installers for 10 years. I now believe I was wrong. Sure
wish I
<br>
could find that written explanation from years ago! Perhaps it came
from CBI
<br>
or some other circuit breaker manufacturer? (see below) Maybe an old
version of the NEC?
<br>
The NEC is the top authority, so please use the same de-rating
guidelines
<br>
for CBI as for thermal breakers.
<br>
Sorry for perpetuating this widely accepted myth.
<br>
</blockquote>
<br>
PS. Robin found this and thinks that this may have been one of the
texts but still
<br>
does not override NEC requirements
<br>
<br>
<blockquote type="cite">From Heinamann:
<br>
</blockquote>
<br>
Continuous operation at 100%current.
<br>
There is no such assurance with a thermal device, which may
<br>
fail to carry rated current when subjected to above normal ambient
<br>
temperatures. A Heinemann breaker rated at 20 amperes, for example,
<br>
will sustain 20 amperes, even at elevated temperatures. Derating
<br>
and other forms of temperature compensation are unnecessary.
<br>
<br>
<br>
<blockquote type="cite">Robin Gudgel
<br>
MidNite Solar
<br>
<br>
</blockquote>
<br>
<br>
<br>
<br>
<br>
<br>
<blockquote type="cite">-------- Original Message --------
<br>
Subject: Re: [RE-wrenches] DC wire sizing
<br>
Date: Fri, 02 Apr 2010 16:35:49 -0600
<br>
From: Allan Sindelar <a class="moz-txt-link-rfc2396E" href="mailto:allan@positiveenergysolar.com"><allan@positiveenergysolar.com></a>
<br>
Reply-To: <a class="moz-txt-link-abbreviated" href="mailto:Allan@positiveenergysolar.com">Allan@positiveenergysolar.com</a>, RE-wrenches
<a class="moz-txt-link-rfc2396E" href="mailto:re-wrenches@lists.re-wrenches.org"><re-wrenches@lists.re-wrenches.org></a>
<br>
<br>
<br>
<br>
Yes, they are 100% duty rated. Also, a little-known fact about the CBI
breakers used by Midnite and Outback, gleaned from conversations with
Robin Gudgel: because of this hydraulic/magnetic construction, all are
capable of controlling both AC and DC, even if not listed as both.
<br>
<br>
*Allan** Sindelar*
<br>
<a class="moz-txt-link-abbreviated" href="mailto:Allan@positiveenergysolar.com">Allan@positiveenergysolar.com</a>
<a class="moz-txt-link-rfc2396E" href="mailto:Allan@positiveenergysolar.com"><mailto:Allan@positiveenergysolar.com></a>
<br>
NABCEP Certified Photovoltaic Installer
<br>
EE98J Journeyman Electrician
<br>
*Positive Energy, Inc.*
<br>
3201 Calle Marie
<br>
Santa Fe, New Mexico 87507
<br>
*505 424-1112*
<br>
<a class="moz-txt-link-abbreviated" href="http://www.positiveenergysolar.com">www.positiveenergysolar.com</a> <a class="moz-txt-link-rfc2396E" href="http://www.positiveenergysolar.com/"><http://www.positiveenergysolar.com/></a>
<br>
<br>
<br>
<br>
robert ellison wrote:
<br>
<blockquote type="cite">I believe that the breakers from CBI,
Midnite and Outback are hydraulic / magnetic and may be operated at
100% While the derating applies to all others that are Thermal /
magnetic,
<br>
<br>
Bob
<br>
<br>
On Fri, Apr 2, 2010 at 11:14 AM, Kent Osterberg <<a class="moz-txt-link-abbreviated" href="mailto:kent@coveoregon.com">kent@coveoregon.com</a>
<a class="moz-txt-link-rfc2396E" href="mailto:kent@coveoregon.com"><mailto:kent@coveoregon.com></a>> wrote:
<br>
<br>
Erika,
<br>
<br>
You should refer to NEC 690.8 this information. There are two
<br>
issues that contribute to the 1.56 factor. First is that the
<br>
maximum current from the PV array is considered the short circuit
<br>
current multiplied by 1.25 to account for higher than standard
<br>
irradiance such as cloud edge effect, high altitude, and high
<br>
operating temperature. The second multiplier of 1.25 is because
<br>
PV current is considered to be continuous. All conductors (and
<br>
breakers) operating continuously (over three hours I believe) that
<br>
are subject to NEC rules are limited to 80% of the ampacity in
<br>
Table 310.16. The two 1.25 factors equals 1.56.
<br>
<br>
For normal operation, wires selected under this criteria are
<br>
conservatively rated. But it is also the objective of the NEC to
<br>
design power systems in a manner that they will remain safe under
<br>
abnormal circumstances.
<br>
<br>
Kent Osterberg
<br>
Blue Mountain Solar, Inc.
<br>
<br>
<br>
<br>
<br>
Erika M. Weliczko wrote:
<br>
<blockquote type="cite"> To my understanding the 156% on PV
source and output circuits is
<br>
related to the ability of PV to deliver more than rated and be
<br>
continuous.
<br>
<br>
Therefore, the wire has to be able to carry this current, so now
<br>
the temperature and fill corrections are applied to find the wire
<br>
capable of the 156%.
<br>
<br>
<br>
I am in a debate where the question is why correct for temp and
<br>
fill on 156% of ISC and spend all that extra money when the
<br>
normal operating is at Imp. Or why correct the 156% but why not
<br>
correct the Isc or Imp.
<br>
<br>
<br>
I am going to stick to the fact that the circuit has to carry the
<br>
156% under all conditions.
<br>
<br>
Thoughts?
<br>
<br>
<br>
Erika
<br>
<br>
<br>
</blockquote>
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