[TenTec] Airpax Breaker Part and Source

[Mike Hyder -N4NT-]

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