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

boB Gudgel boB at midnitesolar.com
Sat Apr 3 13:57:59 PDT 2010 

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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