Parallel String Brain Teaser [RE-wrenches]

Bill Brooks billb at endecon.com
Fri May 24 08:14:19 PDT 2002


Bob-O,

I understand now. I agree that a circuit breaker/disconnect on the array may
be not be necessary for a fault in the array since the fuse will generally
clear before the circuit breaker will trip. However, the circuit breaker
protects the wire from faults in the combined wire or combiner box, so it
still makes sense to use Isc x 1.56 so that it can fuse at the lowest
allowable level for these faults and allow you to use the smallest allowable
wire--would you agree?

Bill.


-----Original Message-----
From: Bob-O Schultze, Electron Connection
[mailto:econnect at snowcrest.net]
Sent: Wednesday, May 22, 2002 7:01 PM
To: RE-wrenches at topica.com
Subject: RE: Parallel String Brain Teaser [RE-wrenches]


Bill,
I should have clarified this further. I have no problem with series
string fuses at Isc x 1.56. They will disconnect a shorted string
from the rest of the pack. The main array disconnect(on the PV side
of the CC), however, if sized at Short circuit x 1.56, becomes a
switch and nothing more.
Bob-O

>Bob-O,
>
>I'm trying to understand your comment. What prevents backfeed to the array
>in the event of a fault with a CC that does not prevent backfeed or that
has
>failed?
>
>What about parallel strings feeding a fault? That is something the CC has
no
>control over.
>
>In these cases the fuse does much more than provide a disconnect in my
>experience.
>
>Bill.
>
>
>-----Original Message-----
>From: Bob-O Schultze, Electron Connection
>[mailto:econnect at snowcrest.net]
>Sent: Monday, May 20, 2002 11:12 AM
>To: RE-wrenches at topica.com
>Subject: RE: Parallel String Brain Teaser [RE-wrenches]
>
>
>Bill and All,
>In my experience, sizing an overcurrent device at Isc X 1.56 per NEC
>on the PV side of the CC pretty much turns whatever you are using
>into a disconnect and nothing more.
>Bob-O
>

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