Calculating string amperages [RE-wrenches]

[William Miller]

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Jay:

Begin citation:

690.8 (D) Sizing of Module Interconnection Conductors. Where a single 
overcurrent device is used to protect a set of two or more 
parallel-connected module circuits, the ampacity of each of the module 
interconnection conductors shall not be less than the sum of the rating of 
the single fuse plus 125 percent of the short-circuit current from the 
other parallel-connected modules.

End citation

Note above where it says "other."

What is not totally clear to me is that in an installation without a 
combiner, i.e. connecting leads through a Square DU HU361 directly to the 
inverter, are we meeting the "single overcurrent device" test of the above 
section?  It seems to me that the internal current limitation 
characteristic of the modules makes the overcurrent protection inapplicable.

This code interpretation is explained pretty thoroughly and convincingly by 
John Berdner in the SMA white paper.  If you have lost the link, I have it 
on our web site:

http://mpandc.com/resources/resources.html

This paper has been universally accepted in the industry and has passed 
muster by the local building inspector code wonk guys.  I used to submit a 
copy with permit applications to forestall questions.

William Miller


At 08:05 AM 2/5/2008, you wrote:

>Hi William,
>
>Where is this subtraction of 1 string located in the code?
>
>thanks,
>
>jay
>peltz power
>On Feb 4, 2008, at 10:18 PM, William Miller wrote:


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