[TenTec] Airpax Breaker Part and Source

[art davis]

I should add that my comments are in no way a reflection on the quality of Airpax products. We used Airpax breakers almost exclusively in the Apollo/Saturn program for both flight vehicle use and ground support equipment applications. Airpax breakers are definitely "top-drawer" components. 

> From: n4uc at hotmail.com
> To: tentec at contesting.com
> Date: Tue, 14 Dec 2010 10:18:41 -0600
> Subject: Re: [TenTec] Airpax Breaker Part and Source
> 
> 
> Yes they do, but you have to look past the marketing and look at the data sheet. According to the trip curve for their "instant" breakers, the typical operating time for current of 2X the breaker rating is just over 100 milliseconds, where the "non-instant breakers can hang in for over a second at the same current. Definitely faster, but far from "instant". In fact the fastest time they are guaranteed to operate is 10 milliseconds and that's at currents at least 8 X the breaker rating (i.e. 160A for a 20A breaker). 
> 
> > From: Mike_N4NT at charter.net
> > To: tentec at contesting.com
> > Date: Tue, 14 Dec 2010 10:49:16 -0500
> > Subject: Re: [TenTec] Airpax Breaker Part and Source
> > 
> > Airpax calls some models "instant," don't they?
> > 
> > ----- Original Message ----- 
> > From: "art davis" <n4uc at hotmail.com>
> > To: "TenTec reflector" <tentec at contesting.com>
> > Sent: Tuesday, December 14, 2010 1:24 AM
> > Subject: Re: [TenTec] Airpax Breaker Part and Source
> > >
> > > I'm no expert, BUT...
> > >
> > > be very careful with the use of the term "instant trip" when referring to 
> > > a circuit breaker or fuse. All circuit protection devices take a finite 
> > > amount of time to operate, no matter what type they happen to be. Look at 
> > > the response curves (i.e. trip curves) for any breaker or fuse and you'll 
> > > see that it may be very quick indeed (less than a millisecond in many 
> > > cases) if the fault current is high enough, but not "instant". And in the 
> > > world of semiconductors very quick might not be fast enough. And look at 
> > > the curves to see the level of current that can flow through the device 
> > > without it tripping at all. You might be surprised.  I may be wrong but I 
> > > doubt that there is any circuit breaker on the market that, when located 
> > > upstream at the power supply, can operate fast enough to protect 
> > > semiconductors from damage due strictly to overcurrent. If the fault 
> > > current is high enough (many times the circuit breaker rating) they may 
> > > offer some limited protection from the heat generated
> > > by the overcurrent flowing through the device, but the semiconductor 
> > > itself must be capable of surviving the current in the first place.
> > >
> > > The primary reason to specify different response time characteristics 
> > > (trip curves) for circuit breakers (slow blow, fast, etc...) is to make 
> > > sure that the power feeder circuit maintains proper trip coordination 
> > > among the various circuit protection devices in the circuit in case of a 
> > > fault in the wiring upstream of the load. In most power distribution 
> > > systems the fuses and circuit breakers upstream of an end user (i.e. 
> > > radio) are there only to protect the wiring between the power source and 
> > > the load. The load (in this case, the radio) must protect itself 
> > > internally.  My guess is that there could be significant damage done 
> > > inside a transceiver long before a 20A breaker all the way back at the 
> > > power supply knew what was happening.
> > >
> > > Of course, the flip side to all this is that it couldn't hurt, right? You 
> > > certainly won't have any protection if you don't use something, so put the 
> > > fastest breaker in there that you can find  and keep your fingers crossed! 
> > > Just don't call it "instant"
> > >
> > > Art, N4UC
> > 
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