---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 10/26/18: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 07:09 AM - Re: Re: Same rating for fuses and circuit breakers? (Robert L. Nuckolls, III) 2. 07:39 AM - Re: Re: Same rating for fuses and circuit breakers? (Robert L. Nuckolls, III) 3. 07:42 AM - Re: Re: Same rating for fuses and circuit breakers? (Robert L. Nuckolls, III) 4. 03:26 PM - Re: Re: Same rating for fuses and circuit breakers? (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 07:09:29 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Same rating for fuses and circuit breakers? > >As for the CB protecting the wires and not the >device...=C2 Well, I have heard that and read that for years. >It does not protect the device ONLY because it >does not function quick enough to prevent damage. >But, as for protecting the wires...=C2 I feel that statement is a BUNK!=C2 =C2 >If it was only to protect the wires WHY doesn't >ALL wires of the same size have the same size CB? >That statement sure sounds like C.Y.A.. >The product manufacture did not want to go the >extra distance - spelt - MONEY.=C2 To add protection to the product! check out the narrative on wire and protection sizing in AC4-13 Circuit protection and wire size can be fine tuned but based mostly on the wire's insulation temperature limits, voltage drop, and environment through which the wire travels. 20 amps through a 22AWG wire in free air will not raise the temperature above the limits for Tefzel wire . . . yet we never see 22AWG operated and/or protected at such extreme. 5A is the legacy rule of thumb limit for 22AWG wire dating back to Mil-w-76 cotton over rubber insulated wire. It's a good rule of thumb that frees the system integrator from what could be a nightmare should his boss task him with 'optimizing' every strand of wire in every wire bundle. The cost/benefit ratio of such a philosophy is exceedingly poor. Having said that, there is noting in the rule of thumb that prohibits departure for calculated reasons . . . like those manufacturers whose products feature some electrical fragility that cries out for external relief. It would be interesting to see a system diagram on a TC aircraft that departs from the 22/5, 20/7, 18/10, 14/15 protocol for 10 degree temperature rise in free air. If one wished to adopt some other policy for temperature rise . . . say 21 degrees C, they're certainly free to do so . . . and the risks are low but so are the benefits. Bob . . . ________________________________ Message 2 _____________________________________ Time: 07:39:14 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Same rating for fuses and circuit breakers? At 08:05 PM 10/25/2018, you wrote: >Thanks Don, > >Ya know guys, the circuit is so simple it can be >added to a CB.=C2 probably easier than a fuse. >Good for the CB that is out of the standard field of view. > >Barry But what is the cost/benefit ratio? 99.99% of all breakers/fuses installed in all vehicles at the factory go to the junkyard never having been tasked to do their job. For every fault that takes a system down by opening the power feeder protection, there are MANY more faults equally deleterious to system operation that do not open the feeder protection. When circuit protection does operate in a thoughtfully designed system, the thing is broke. Resetting the breaker or replacing the fuse will not bring it back. The pilot's first clue that something is amiss is when an expected event doesn't occur on the airplane . . . but what value is there in knowing the state of power feeder protection? The reason for malfunction is not relevant to the pilot's prime directive: effect a return to earth without bending airplanes or people. Indicating fuses are cute but the feature saves only seconds of diagnostic time which is done on the ground. Bob . . . ________________________________ Message 3 _____________________________________ Time: 07:42:31 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Same rating for fuses and circuit breakers? At 07:29 PM 10/25/2018, you wrote: >Right You Are Charlie: > >Here is another thought? >In the AC world there is a thing know as a Ground Fault Interrupt (GFI) Yup, got 'em in airplanes too. After the Swiss Air 111 disaster there was a push to develop a breaker with soft-fault detection built in. TI and others rose to the occasion and you can buy such critters today . . . if your wallet is fat enough. Anybody work for Boeing or Airbus? Know anybody who might fill us in on just how many such devices have found their way onto there products? I'm betting its VERY few if any. Bob . . . ________________________________ Message 4 _____________________________________ Time: 03:26:57 PM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Same rating for fuses and circuit breakers? > >I do recall years ago there were fuse holders >for AC that would glow when the fuse blew.=C2 It >was a simple circuit of a NE2 bulb and a series >resistor.=C2 They were wired in series across the >fuse.=C2 When the fuse blew the circuit would >become active and the NE2 would glow. >Is this the same idea? Yup . . . they're still made https://tinyurl.com/ych5z2u7 Just one of a family of devices called 'indicating' fuse holders. Some of these critters have a little spring loaded arm that pops up or a button that pops out. https://tinyurl.com/y8a9qkd5 These features have been used to make contact with a 'detector strip' of some type that will effect an alarm when a blown fuse does its thing . . . The idea isn't new . . . back in 1928 a clever fellow got a patent on a system for bridging an opaque cartridge fuse with a transparent device. He correctly reasoned that when the large fuse opens in relative obscurity, the external device would open as well and announce the condition. http://www.freepatentsonline.com/1868465.pdf Wonder if he ever collected a royalty on this . . . Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.