Parallel String Brain Teaser [RE-wrenches]

[Bob-O Schultze, Electron Connection]

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Bill,
No, unless you are going straight to the battery from the combiner 
box with your PV home runs. In that case, the stored energy in the 
battery will be plenty to trip the CB or fuse rated at Isc x 1.56. 
Assuming a main OCD on both sides of the CC, the one on the PV side 
will NEVER trip under any conditions you can present unless both the 
CC AND the CC-to-Battery OCD shorts AND there is a fault in the PV 
home run.. Ridiculous. While the reality is that is probably far 
cheaper and easier to use a 2 pole fused disco or a second CB there 
than just a switch, rating that overcurrent device at Isc x 1.56 
makes it a switch and nothing more.
Best, Bob-O

>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

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