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"
> Date: Mon, 13 Dec 2010 20:54:08 -0500
> From: firstname.lastname@example.org
> To: email@example.com
> CC: firstname.lastname@example.org
> Subject: Re: [TenTec] Airpax Breaker Part and Source
> Most Ten Tec owners seem to be going to Poco Sales
> (http://www.pocosales.com/). They have a minimum order of $25. The
> breaker that you have looks like the Ten Tec 1140, which was used for
> the Corsair and similar rigs. The "0" after the T11 indicates an instant
> trip breaker, which, according to Poco, is very scarce. I exchanged some
> e-mail correspondence with them about a week ago. Here is what they
> "The 20A quoted below has been put to use in hundreds of Ten-Tec
> applications and none have yet to complain."
> T11-1-20.0A-01-11C-V @ $12.50/ea
> Parts are in stock
> They know about the 17.5 amp instant trip requirement, but they do not
> stock such a breaker.
> I am looking for a fast trip 5 amp breaker for my Century 22, but
> that is not a stock item, either (8 weeks lead time). They do stock
> slow trip breakers but I don't think they are fast enough to protect
> the finals, which is why Ten Tec specified instant or fast trip breakers.
> If you only need one breaker, you can probably team up with a couple of
> other guys to make the minimum order.
> Bob WB2VUF
> On 12/13/2010 9:31 AM, Curt wrote:
> > I'm looking for best part number and source for an Airpax magnetic breaker
> > for less than 18A. I think the correct number is T11-0-17.5A-01-10A-V.
> > Appreciate any advice about this.
> > 73, Curt KB5JO
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