QO Breakers and Panels [RE-wrenches]

[William Miller]

Colleagues:

I just finished a telephone call with Square D tech support.  They are
going to fax me critical information which I will share as soon as it
arrives and I have time to transcribe it.

I have a question about Drake's post, below:


At 10:03 AM 3/8/01 -0800, you wrote:
>Hi Bill,
>
>
>What ever the reason might be, it convinced me that fuses are superior 
>protection to breakers.  As you stated before, the QO breaker makes an 
>excellent switch for low voltage DC.  I think it is good for PV array 
>disconnects, as they are current limited.  On the battery side, I don't 
>trust the QO as the sole protection.
>
>Drake

Q: If we are using a DC rated circuit breaker to connect PV source circuits
to a battery charging system, then don't we have a battery connection at
the load side?  For example, in a TC60 with breaker option with the breaker
wired in the output circuit: the breaker will be connected to the battery
bank.  In this case then, one should always install a fuse between the
breaker and the batteries, correct?  Then why even have a breaker?  Why not
instead use a switch with adequate interrupting capacity?  See ASCII CAD
below:

Typical PV source and charging circuit:

PV array---DC breaker-----\
                                       ----Charge
control---Switch-------fuse--batteries
PV array---DC breaker-----/


Thanks again for the great dialog.  We need these answers so we can design
reliable and legal installations.


William

__________________________________________________________________
William Miller
SLO Communications: Communications and Power Systems Consulting
PO Box 50, Santa Margarita, CA 93453
Voice :805-438-5600		Fax: 805-438-4607	VMail: 805-546-4875
email: wrmiller at slonet.org
License No. C-10-773985
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