Parallel String Brain Teaser [RE-wrenches]

Bill Brooks billb at endecon.com
Sun May 19 22:46:03 PDT 2002


Drake,

The statement you asked about below is referring to the fact that if you are
paralleled with another string of SP75 modules, they have a 6-amp max short
circuit current according to NEC 690-8 so we have to subtract that 6 amps
from the 15-amp series fuse rating (15 - 6 = 9 amps), so that the total does
not exceed 15 amps. But we can't put in a 9 amp fuse (I think you got that
part).

Sorry for the confusion.

Bill.


-----Original Message-----
From: Drake Chamberlin [mailto:solar at eagle-access.net]
Sent: Friday, May 17, 2002 8:31 PM
To: RE-wrenches at topica.com
Subject: Re: Parallel String Brain Teaser [RE-wrenches]


Hello Bill,

At 04:32 PM 5/17/02 -0600, you wrote: (in this case I wrote)

>Also, I am confused as to why we can't use 15 amps for the series fuse
>size instead of 9.

Got it.  Your point seems well taken, that current from other strings could
back feed through a 15 amp series fuse.  That current, combined with the
current from the parallel string behind the same fuse would add up to more
than 15 amps.

But I'm still confused about the following statement:

"Take the output of one string plus the string fuse and you get 9 amps
(fuse)"


Thanks,

Drake

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