QO Breakers and Panels [RE-wrenches]

[Bill Brooks]

Cool, were you able to measure the initial burst of current. Not sure if it
matters, but if you can get more than 5000 amps for a few milliseconds, it
might be enough to destroy the breaker before it has a chance to react. Your
assessment seems right-on about needing current limiting fuses. Good
testimonial on why they are needed.

Bill.


-----Original Message-----
From: Drake Chamberlin - Electrical Energy
[mailto:solar at eagle-access.net]
Sent: Wednesday, March 07, 2001 8:56 AM
To: RE-wrenches at topica.com
Subject: RE: QO Breakers and Panels [RE-wrenches]


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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____________________________________________________________
T O P I C A  -- Learn More. Surf Less. 
Newsletters, Tips and Discussions on Topics You Choose.
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