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Re: [TenTec] Speed of fuses versus circuit breakers

To: tentec@contesting.com
Subject: Re: [TenTec] Speed of fuses versus circuit breakers
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
Reply-to: geraldj@storm.weather.net,Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sat, 22 Sep 2007 22:15:01 -0600
List-post: <mailto:tentec@contesting.com>
On Sat, 2007-09-22 at 10:09 -1000, Ken Brown wrote:
> >  Having checked the "fast" acting circuit breaker's
> > curve, I use an automotive fuse of the miniature tag style rated at 15
> > amps. 
> >   
> There was a discussion about the relative speeds of circuit breakers 
> versus fuses on this reflector some time ago. I stated that my gut 
> feeling was that fuses might very well be much quicker responding, based 
> on less mass having to move a shorter distance in order for the circuit 
> to be interrupted. I was told that my gut feeling was wrong, wrong, 
> wrong. Can you refer me to a web site or sites that will show circuit 
> breaker and fuse response times? I would like to replace my gut feeling 
> with some real measured data.
I looked at circuit breaker curves at the Airpax web site. I may have
looked at fuse curves on the Buss site or in my thick binder of Buss
catalogs and data sheets. Remember I'm running the fuse AT 125% of
nameplate rating to speed it up more. I do get "nuisance" trips, but
they save the PA.

The fuse wire doesn't have to move so much as it has to heat enough to
melt. And how much it has to heat depends on the alloy which may be
different according to the rating though in the automotive fuses after
plating, it looks like the fuse is stamped of the same brass as the
blades. I think that's not quite true but the Chinese fuses that
sometimes don't blow may have been made that way. According to engineers
on some tractor pages I frequent, the fuses that did the most damage
came from Harbor Freight kits.
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer

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