QO Breakers and Panels [RE-wrenches]

Drake Chamberlin - Electrical Energy solar at eagle-access.net
Wed Mar 7 08:55:33 PST 2001


<x-flowed>Hi Wrenches,

I saw a QO breaker fail on 24 volt battery voltage.  The length of the run 
was sufficient to keep the maximum short circuit current well under 5000 
amps.  The breaker did not trip, but allowed a #10 wire to burn a fair 
chunk out of a cover plate and junction box, and finally burn the wire in 
two.  I always recommend using DC current limiting fuses between batteries 
and QO breakers.

Drake


At 08:43 PM 03/06/2001 -0800, you wrote:
>Wrenches,
>
>Can't let this one go. First of all--I love QO breakers. They make the best
>low voltage switches money can buy. BUT, I have personally witnessed a QO
>fry at about 70 volts with a DC motor load (kind of worst case scenario).
>The dc-rating in the Square D digest is 48 volts. Pulse got special ratings
>on QOU breakers to use in their 48-Volt DC systems, but that does not mean
>that we are allowed to do the same.

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