X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 06 Nov 2007 16:28:45 -0500 Message-ID: X-Original-Return-Path: Received: from [206.246.194.60] (HELO visi.net) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTP id 2457542 for lml@lancaironline.net; Mon, 05 Nov 2007 22:25:03 -0500 Received-SPF: none receiver=logan.com; client-ip=206.246.194.60; envelope-from=rpastusek@htii.com X-Virus-Scanner-Engine: ClamAV Received: from [69.143.130.212] (account rpastusek@htii.com HELO dlhtpax009) by visi.net (CommuniGate Pro SMTP 4.2) with ESMTP id 241424349 for lml@lancaironline.net; Mon, 05 Nov 2007 21:49:50 -0500 From: "Robert Pastusek" X-Original-To: "'Lancair Mailing List'" References: In-Reply-To: Subject: RE: [LML] Design for Circuit Breakers & Fuses? X-Original-Date: Mon, 5 Nov 2007 21:50:10 -0500 X-Original-Message-ID: <037801c8201f$c47228b0$4d567a10$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0379_01C81FF5.DB9C20B0" X-Mailer: Microsoft Office Outlook 12.0 Thread-Index: AcgfU7DbfRM2JXpfRVu5xiZzePTtKAAygnWA Content-Language: en-us This is a multipart message in MIME format. ------=_NextPart_000_0379_01C81FF5.DB9C20B0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Valin Thorne wrote: I'm looking for opinions on the use of circuit breakers and/or fuses in our Legacy under construction. . Valin, I have three circuit breakers in my iV-P, one each for the primary and backup alternator field circuits, and one for the main hydraulic pump. Consider wiring the hyd pressure switch "downstream" of this large CB so you will disconnect relay power as well as pump power when it's pulled. Otherwise, the intermittent-rated relay remains energized if you pull the pump CB with pressure below the pre-set turn-on. The alternator field CB's allow each to be shut down independently of the other, and of the rest of the electrical system, should you have a run-away. Everything else is on fuses. I have four fuse panels from B&C in the airplane, a home-made one on the side of the battery box in the engine compartment, plus a few in-line fuses where it made better sense to do this-e.g. the hydraulic pump "on" sensing circuit. This uses a 24 v signal from the pump side of the relay to illuminate a warning light on the panel. This 22 AWG wire is toast if any part of the circuit is shorted with the pump energized, so I put an in-line fuse back with the pump relay. Rational is that the small fuse (1 A) protects the wiring, and the system works just fine without the warning light, so the the fuse can be changed if/when needed. I have a 10- and 20-position B&C fuse panel hinged to the forward bottom of the instrument panel just over the co-pilot's knees. It latches behind the panel with the fuses pointing downward above the passenger knees, and unfolds "face up" to rest on the passenger legs for checking/changing fuses. These panels power all the instrument systems (to include the fuel probe oscillators out in each wing tip), and are continuously fed by both electrical systems through high power/high quality diodes. The other main fuse location is on the right passenger side of the fuselage. Most aircraft systems beyond the instrument panel are fused through this pair of panels. They hang vertically and are hinged at the top to lift up for access/visibility, and are completely concealed by a Velcro'd cover built into the fuselage side panel. Although I plan to carry spares for each type/size of fuse I used, my general plan is to carry on with whatever remains after a "pop" and sort it out on the ground. In more than 40 years of flying, including 25+ in AF fighters, I don't recall a situation that resetting a popped CB restored the function-and I had two occasions where attempting caused much more serious problems. I know that resetting occasionally works-such as with a lightning strike-but this never worked for me either. So, IAW Bob Nuckols' recommendation, I used CB's only for equipment I thought I might need to shut down in flight (e.g the hydraulic pump) and that doesn't have it's own switch. I used fuses for all else, and don't plan to routinely change them out in flight. The cost of fuses is about 10% of good CB's, they are lighter, faster and easier to install, and take up less space. Let me know what you decide, or if you want additional information. BOB ------=_NextPart_000_0379_01C81FF5.DB9C20B0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Valin Thorne wrote:

I’m looking for opinions on the use of circuit = breakers and/or fuses in our Legacy under construction.  = …

 

 

Valin,

 

I have three circuit breakers in my iV-P, one each for = the primary and backup alternator field circuits, and one for the main hydraulic = pump. Consider wiring the hyd pressure switch “downstream” of this large CB = so you will disconnect relay power as well as pump power when it’s pulled. Otherwise, the = intermittent-rated relay remains energized if you pull the pump CB with pressure below the = pre-set turn-on. The alternator field CB’s allow each to be shut down = independently of the other, and of the rest of the electrical system, should you have a run-away.

 

Everything else is on fuses. I have four fuse panels from B&C in the airplane, a home-made one on the side of the battery box = in the engine compartment, plus a few in-line fuses where it made better sense = to do this—e.g. the hydraulic pump “on” sensing circuit. = This uses a 24 v signal from the pump side of the relay to illuminate a warning light on the panel. = This 22 AWG wire is toast if any part of the circuit is shorted with the pump = energized, so I put an in-line fuse back with the pump relay. Rational is that the = small fuse (1 A) protects the wiring, and the system works just fine without = the warning light, so the the fuse can be changed if/when needed. =

 

I have a 10- and 20-position B&C fuse panel hinged to = the forward bottom of the instrument panel just over the co-pilot’s = knees. It latches behind the panel with the fuses pointing downward above the passenger = knees, and unfolds “face up” to rest on the passenger legs for = checking/changing fuses. These panels power all the instrument systems (to include the = fuel probe oscillators out in each wing tip), and are continuously fed by both = electrical systems through high power/high quality diodes.

 

The other main fuse location is on the right passenger = side of the fuselage. Most aircraft systems beyond the instrument panel are fused = through this pair of panels. They hang vertically and are hinged at the top to = lift up for access/visibility, and are completely concealed by a Velcro’d = cover built into the fuselage side panel.

 

Although I plan to carry spares for each type/size of = fuse I used, my general plan is to carry on with whatever remains after a = “pop” and sort it out on the ground. In more than 40 years of flying, including = 25+ in AF fighters, I don’t recall a situation that resetting a popped CB = restored the function—and I had two occasions where attempting caused much more = serious problems. I know that resetting occasionally works—such as with a = lightning strike—but this never worked for me either.

 

So, IAW Bob Nuckols’ recommendation, I used = CB’s only for equipment I thought I might need to shut down in flight (e.g the = hydraulic pump) and that doesn’t have it’s own switch. I used fuses = for all else, and don’t plan to routinely change them out in flight… =

 

The cost of fuses is about 10% of good CB’s,  = they are lighter,  faster and easier to install, and take up less space.

 

Let me know what you decide, or if you want additional information.

 

BOB

 

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