Calculating string amperages [RE-wrenches]

[Ray Walters]

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Hi William;

I noticed that change in the series fuse rating about the time they  
changed to the MC connectors and changed the module dimensions  
slightly too. I caught it last summer? But I had thought about three  
strings with the old numbers too.

Ray


On Feb 26, 2008, at 5:59 PM, William Miller wrote:

>
> Ray, Colleagues:
>
> I have been scratching my head ever since Ray sent me the e-mail  
> below.  I was very certain that at one point in time I had been  
> convinced by a Fronius engineer that 3 strings of Solar World  
> modules are allowed without fusing.  When Ray sent this e-mail,  
> rechecked my calculations and found that they do not work.
>
> Just now I realized that Solar World changed the specified series  
> fuse ratings sometime in the recent past.  In 2006 and before, the  
> SW175 had a series fuse rating of 20 amps, which allowed the three  
> strings ((3-1)*5.3*1.56<20).  I actually found a photo of a module  
> label if anyone really needs documentation on this.
>
> The series fuse rating now is 15 amps and three strings are not  
> allowed.  Two strings are allowed.
>
> I apologize, Ray, for leaving this hanging.  My memory is not what  
> it used to be.
>
> William
>
>
>
> At 11:11 AM 2/8/2008, you wrote:
>
>
>> Well we do have some discrepancies here. William was saying we could
>> go to 3 parallel Solar World strings, John Berdner here says only
>> one, and I'm still saying 2 is good.
>> John I have 2 issues with your excellent analysis.
>> 1) 690.8 B) (1) exception: "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 its rating."
>> This means that with the right breaker, we don't have to use the 1.56
>> multiplier for array current, only 1.25 which is for edge of cloud
>> effect, etc. I have seen Solar world modules exceed their nameplate
>> rating, so this multiplier is appropriate.
>> 2 x 5.1 A x 1.25 = 12.75 Amps on a 15A breaker that is rated for 100%
>> duty is acceptable. (most Outback and Midnite solar offerings are
>> 100% rated BTW)
>>
>>
>> R. Walters
>> Solarray.com
>> NABCEP # 04170442
>
>
>
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R. Walters
Solarray.com
NABCEP # 04170442	




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