Mailing List flyrotary@lancaironline.net Message #35513
From: Al Gietzen <ALVentures@cox.net>
Subject: CBs and fuses
Date: Sat, 17 Feb 2007 15:10:22 -0800
To: 'Rotary motors in aircraft' <flyrotary@lancaironline.net>

 

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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