X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 30 [X] Return-Path: Received: from fed1rmmtao104.cox.net ([68.230.241.42] verified) by logan.com (CommuniGate Pro SMTP 5.1.6) with ESMTP id 1844363 for flyrotary@lancaironline.net; Sat, 17 Feb 2007 18:11:05 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.42; envelope-from=alventures@cox.net Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao104.cox.net (InterMail vM.7.05.02.00 201-2174-114-20060621) with ESMTP id <20070217231010.EXNE22948.fed1rmmtao104.cox.net@fed1rmimpo01.cox.net> for ; Sat, 17 Feb 2007 18:10:10 -0500 Received: from BigAl ([72.192.132.90]) by fed1rmimpo01.cox.net with bizsmtp id QnAA1W00B1xAn3c0000000; Sat, 17 Feb 2007 18:10:10 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: CBs and fuses Date: Sat, 17 Feb 2007 15:10:22 -0800 Message-ID: <000001c752e8$ccead1e0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C752A5.BEC791E0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C752A5.BEC791E0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Eurocopter Factory Instructors are VERY COMPETENT in Eurocopter Helicopter Systems!! There is absolutely NO doubt that he knows the difference between fuses and breakers and WHY either one would be used. Thomas; Certainly not impugning the competence of the flight instructors; just suggesting the design engineers may have other reasons than cost. One may be reliability. The reliability of CBs goes down significantly after they have experienced a 'trip'. I recall reading one experts opinion that a CB should be replaced after a 'trip'. Yeah; seems extreme. The modern philosophy of circuit design is to design for fault tolerance, so a fault; once causing the protection device to open, is left for repair when you land. The key for using fuses is fault tolerant circuit design and proper selection and sizing of fuses. Having done this; studies suggest that the fuse offers higher reliability and lower cost. There certainly reasons for either CBs or fuses, and I have both in my plane. For my flight critical circuits I opted for simple, fault tolerance and fuses. I wouldn't argue with someone making a different choice. FWIW, Al ------=_NextPart_000_0001_01C752A5.BEC791E0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

Eurocopter Factory = Instructors are VERY COMPETENT in Eurocopter Helicopter Systems!!

There is absolutely NO doubt that he knows = the difference between fuses and breakers and WHY either one would be = used.

 

Thomas; 

Certainly not impugning the = competence of the flight instructors; just suggesting the design engineers may have = other reasons than cost.  One may be reliability.  The reliability of CBs = goes down significantly after they have experienced a ‘trip’.  I = recall reading one experts opinion that a CB should be replaced after a = ‘trip’.  Yeah; seems extreme.  The modern philosophy of circuit design = is to design for fault tolerance, so a fault; once causing the protection device to = open, is left for repair when you land.

 

The key for using fuses is fault tolerant circuit design and proper selection and sizing of fuses.  = Having done this; studies suggest that the fuse offers higher reliability and = lower cost.

 

There certainly reasons for = either CBs or fuses, and I have both in my plane.  For my flight critical = circuits I opted for simple, fault tolerance and fuses.  I wouldn’t = argue with someone making a different choice.

 

FWIW,

 

Al

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