X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 30 Apr 2008 20:14:31 -0400 Message-ID: X-Original-Return-Path: Received: from smtp123.sbc.mail.sp1.yahoo.com ([69.147.64.96] verified) by logan.com (CommuniGate Pro SMTP 5.2.2) with SMTP id 2878822 for lml@lancaironline.net; Wed, 30 Apr 2008 14:50:14 -0400 Received: (qmail 90763 invoked from network); 30 Apr 2008 18:50:13 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=sbcglobal.net; h=Received:X-YMail-OSG:X-Yahoo-Newman-Property:Message-ID:From:To:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=m3dF2jwmYEj1f59mMayUy7XULMNMFBXY1YunEQS9k//gxUwGwhmM1UVvudj0A4WTb9qZa8zJ7aW1r4gOJErnHIMAuPYLo6nBbwSDphUNsz3RrCEQS7QcLG6a4FP/DqFqM+sbGOCepJr6EjhiJ088eCvLK2QHz5EwyykdByzLJ6Y= ; Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@75.15.158.59 with login) by smtp123.sbc.mail.sp1.yahoo.com with SMTP; 30 Apr 2008 18:50:13 -0000 X-YMail-OSG: awvkuaUVM1nv5maNJ_yWrPUte2f.kac5e_v1OXkLKgO.0KxzD2KpyOEyh8rt6mUJULOfJWtSan79cQqdYJbaj_vOcDsGDJJuXMnIn1Sklylw8rCLcA_Z3IGhOlcyW9s4J24sm4hz7vm2WTUK2o0wKWTDefGCKIsclCvvqsn5Agp5i8jhvM4- X-Yahoo-Newman-Property: ymail-3 X-Original-Message-ID: <000a01c8aaf3$073b22b0$3b9e0f4b@Computerroom> From: "Paul Lipps" X-Original-To: "Marv Kaye" Subject: Circuit protection X-Original-Date: Wed, 30 Apr 2008 11:50:13 -0700 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0007_01C8AAB8.59D14350" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_0007_01C8AAB8.59D14350 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable All of you using circuit breakers and fuses should be aware of the = operating characteristics of these devices. With the exception of = magnetic circuit breakers, fuse's and thermal circuit breaker's = characteristics are affected by ambient temperature. I'm not quite sure = where you would use a fuse in an aircraft application except for some = ancillary device that has no direct effect on the aircraft operation; I = use one in my air-horn circuit. Typically, a circuit protection device = is to protect the wiring. not the load, but in some applications that = may not hold true.The Littlefuse data sheet says that you should use a = fuse at 75% of its 25C rated value in order to prevent nuisance blowing. = At an ambient temperature of 80C, 176F, the fuse should be de-rated to = 95% of its 25C rating. If you are using one of the re-settable PTC = devices, it is de-rated linearly to 40% at 90C ambient. W23/W31 series = thermal cuircuit breakers de-rate linearly to 70% at an ambient = temperature of 60C, 140F, of their nominal 25C rating. Note that these = breakers will not trip at their rated value at 100% of their de-rated = rating, and will trip in one hour at 135% of rating. Depending on the = breaker size 5-50A breakers trip at 200% in 6-22 seconds, whereas 0.5-4A = breakers trip in 11-30 seconds at 200%. The reason I am bringing this up = is that if you are using one of these devices in a hot area, such as = within a closed box with other heat-producing devices, or at the top of = the firewall in the engine compartment, you may not get the operation = you think is taking place! ------=_NextPart_000_0007_01C8AAB8.59D14350 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
All of you using circuit breakers and fuses = should be=20 aware of the operating characteristics of these devices. With the = exception of=20 magnetic circuit breakers, fuse's and thermal circuit breaker's = characteristics=20 are affected by ambient temperature. I'm not quite sure where you would = use a=20 fuse in an aircraft application except for some ancillary device that = has no=20 direct effect on the aircraft operation; I use one in my air-horn = circuit.=20 Typically, a circuit protection device is to protect the wiring. not the = load,=20 but in some applications that may not hold true.The Littlefuse data = sheet says=20 that you should use a fuse at 75% of its 25C rated value in order = to=20 prevent nuisance blowing. At an ambient temperature of 80C, 176F, = the fuse=20 should be de-rated to 95% of its 25C rating. If you are using one of the = re-settable PTC devices, it is de-rated linearly to 40% at 90C = ambient.=20 W23/W31 series thermal cuircuit breakers de-rate linearly to 70% at an = ambient=20 temperature of 60C, 140F, of their nominal 25C rating. Note that = these=20 breakers will not trip at their rated value at 100% of their de-rated = rating,=20 and will trip in one hour at 135% of rating. Depending on the breaker = size 5-50A=20 breakers trip at 200% in 6-22 seconds, whereas 0.5-4A breakers trip = in=20 11-30 seconds at 200%. The reason I am bringing this up is that if you = are using=20 one of these devices in a hot area, such as within a closed box with = other=20 heat-producing devices, or at the top of the firewall in the engine = compartment,=20 you may not get the operation you think is taking=20 place!
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