[RE-wrenches] [Fwd: Re: DC wire sizing]

boB Gudgel boB at midnitesolar.com
Sat Apr 3 23:09:23 PDT 2010


Kent Osterberg wrote:
> Thanks Robin.  I've long been suspicious that the CBI circuit breakers 
> should not be run at 100% for a couple reasons:
> 1) I've seen too many 60-amp CBI breakers on charge controllers trip 
> habitually.  But a replacement 60-amp breaker works fine.
> 2) Nothing in the CBI literature that is available on their web site 
> says the QY breakers are rated to operate at 100%.
> 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. 
> 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. 
>
> Kent Osterberg
> Blue Mountain Solar, Inc.
>

HI Kent and Allan    (isn't that the name of a TV show, a movie or 
furniture store ?)....

More from Robin.   I'm just relaying, but you can email him off list for 
more info if you like
and take it from here unless there is something substantial to report.
Thanks,
boB

I have found enough information now from manufactures like CBI, Carling,
Heinemann and others that claim Hydraulic/magnetic breakers do not need to
be de-rated. It is not in the NEC, but Allan may be correct that if the
manufacturer says de-rating is not required, then it isn't required. Do a
Google search on "hydraulic/magnetic de-rating" You will find a lot of
information that substantiates the old myth. I was trying to find it in the
NEC, but it isn't there. I'm going back to my myth!
Robin Gudgel





>
> boB Gudgel wrote:
>>
>> Forwarding a message from Robin Gudgel...
>>
>> Robin Gudgel wrote:
>>> The CBI QY series of DC breakers have an arc shoot that is required to
>>> quench a DC arc. This breaker would work just fine as an AC breaker 
>>> although
>>> is not marked as such. I am not sure if the AC breakers (QL, QZ and QZD
>>> series) have the arc shoot. I was told years ago by CBI that the AC 
>>> and DC
>>> breakers are built the same, but I had never broke one open to see 
>>> if the
>>> arc shoot is present on AC breakers until today. The AC breakers do 
>>> in fact
>>> have the same arc shoot as the DC breakers. CBI just marks the 
>>> outside of
>>> the breakers differently. You don't want to get called on the AC vs. DC
>>> issue by an inspector because you are going to lose that battle. It 
>>> makes
>>> things a bit confusing to have a DC breaker in an AC circuit even 
>>> though
>>> they are identical inside. I believe Allan Sindelar was in the field 
>>> and had
>>> a situation where it saved a bunch of time and hassle to use a QY 
>>> breaker
>>> instead of a QL that he did not have on hand. I had told him that 
>>> the DC
>>> breaker would function just fine as an AC breaker. That installation 
>>> was
>>> safe, but an inspector would probably make you change to an AC breaker.
>>>
>>> I remember years ago seeing in print that a Hydraulic/Magnetic 
>>> breaker could
>>> be used at 100% duty rating where as a thermal breaker could only be 
>>> used at
>>> 80%. I have searched and searched to find this written explanation 
>>> again to
>>> no avail. I thought it was in the NEC, but I now believe I was 
>>> wrong. If the
>>> NEC does not allow the use of H/M breakers to be used at 100% duty 
>>> cycle,
>>> then it just is not allowed. It is true that the H/M breakers are not
>>> affected by temperature like thermal breakers are, but that in itself
>>> doesn't overrule the NEC. I personally have been spreading this myth to
>>> hundreds of installers for 10 years. I now believe I was wrong. Sure 
>>> wish I
>>> could find that written explanation from years ago! Perhaps it came 
>>> from CBI
>>> or some other circuit breaker manufacturer? (see below) Maybe an old 
>>> version of the NEC?
>>> The NEC is the top authority, so please use the same de-rating 
>>> guidelines
>>> for CBI as for thermal breakers.
>>> Sorry for perpetuating this widely accepted myth.
>>>   
>>
>> PS.  Robin found this and thinks that this may have been one of the 
>> texts but still
>> does not override NEC requirements
>>
>>> From Heinamann:
>>
>> Continuous operation at 100%current.
>> There is no such assurance with a thermal device, which may
>> fail to carry rated current when subjected to above normal ambient
>> temperatures. A Heinemann breaker rated at 20 amperes, for example,
>> will sustain 20 amperes, even at elevated temperatures. Derating
>> and other forms of temperature compensation are unnecessary.
>>
>>
>>> Robin Gudgel
>>> MidNite Solar
>>>
>>>   
>>
>>
>>
>>
>>
>>
>>> -------- Original Message --------
>>> Subject:     Re: [RE-wrenches] DC wire sizing
>>> Date:     Fri, 02 Apr 2010 16:35:49 -0600
>>> From:     Allan Sindelar <allan at positiveenergysolar.com>
>>> Reply-To:     Allan at positiveenergysolar.com, RE-wrenches 
>>> <re-wrenches at lists.re-wrenches.org>
>>>
>>>
>>>
>>> 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.
>>>
>>> *Allan** Sindelar*
>>> Allan at positiveenergysolar.com <mailto:Allan at positiveenergysolar.com>
>>> NABCEP Certified Photovoltaic Installer
>>> EE98J Journeyman Electrician
>>> *Positive Energy, Inc.*
>>> 3201 Calle Marie
>>> Santa Fe, New Mexico 87507
>>> *505 424-1112*
>>> www.positiveenergysolar.com <http://www.positiveenergysolar.com/>
>>>
>>>
>>>
>>> robert ellison wrote:
>>>  
>>>> 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,
>>>>  
>>>> Bob
>>>>
>>>> On Fri, Apr 2, 2010 at 11:14 AM, Kent Osterberg 
>>>> <kent at coveoregon.com <mailto:kent at coveoregon.com>> wrote:
>>>>
>>>>     Erika,
>>>>
>>>>     You should refer to NEC 690.8 this information.  There are two
>>>>     issues that contribute to the 1.56 factor.  First is that the
>>>>     maximum current from the PV array is considered the short circuit
>>>>     current multiplied by 1.25 to account for higher than standard
>>>>     irradiance such as cloud edge effect, high altitude, and high
>>>>     operating temperature.  The second multiplier of 1.25 is because
>>>>     PV current is considered to be continuous.  All conductors (and
>>>>     breakers) operating continuously (over three hours I believe) that
>>>>     are subject to NEC rules are limited to 80% of the ampacity in
>>>>     Table 310.16.  The two 1.25 factors equals 1.56.
>>>>
>>>>     For normal operation, wires selected under this criteria are
>>>>     conservatively rated.  But it is also the objective of the NEC to
>>>>     design power systems in a manner that they will remain safe under
>>>>     abnormal circumstances.
>>>>
>>>>     Kent Osterberg
>>>>     Blue Mountain Solar, Inc.
>>>>
>>>>
>>>>
>>>>
>>>>     Erika M. Weliczko wrote:
>>>>    
>>>>>     To my understanding the 156% on PV source and output circuits is
>>>>>     related to the ability of PV to deliver more than rated and be
>>>>>     continuous.
>>>>>
>>>>>     Therefore, the wire has to be able to carry this current, so now
>>>>>     the temperature and fill corrections are applied to find the wire
>>>>>     capable of the 156%.
>>>>>
>>>>>     
>>>>>     I am in a debate where the question is why correct for temp and
>>>>>     fill on 156% of ISC and spend all that extra money when the
>>>>>     normal operating is at Imp. Or why correct the 156% but why not
>>>>>     correct the Isc or Imp.
>>>>>
>>>>>     
>>>>>     I am going to stick to the fact that the circuit has to carry the
>>>>>     156% under all conditions.
>>>>>
>>>>>     Thoughts?
>>>>>
>>>>>     
>>>>>     Erika
>>>>>
>>>>>
>>>>>       
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