X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 2 [X] Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 09 Apr 2007 13:52:49 -0400 Message-ID: X-Original-Return-Path: Received: from vms048pub.verizon.net ([206.46.252.48] verified) by logan.com (CommuniGate Pro SMTP 5.1.8) with ESMTP id 1974542 for lml@lancaironline.net; Sun, 08 Apr 2007 15:10:28 -0400 Received: from jacky0da39824a ([71.111.169.130]) by vms048.mailsrvcs.net (Sun Java System Messaging Server 6.2-6.01 (built Apr 3 2006)) with ESMTPA id <0JG7003JP18YMWE8@vms048.mailsrvcs.net> for lml@lancaironline.net; Sun, 08 Apr 2007 14:10:13 -0500 (CDT) X-Original-Date: Sun, 08 Apr 2007 12:09:55 -0700 From: "Tom Gourley" Subject: [LML] Wire Chafing X-Original-To: "Lancair Mailing List" Reply-to: "Tom Gourley" X-Original-Message-id: <002e01c77a11$7f0894d0$650610ac@jacky0da39824a> MIME-version: 1.0 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 X-Mailer: Microsoft Outlook Express 6.00.2900.3028 Content-type: multipart/alternative; boundary="----=_NextPart_000_002B_01C779D6.D1FBC990" X-Priority: 3 X-MSMail-priority: Normal References: This is a multi-part message in MIME format. ------=_NextPart_000_002B_01C779D6.D1FBC990 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Here's something to think about the next time you're using a cable tie = to secure wiring. A couple of days ago my wife told me that the circuit = breaker for the circulating fans in one of her greenhouses was tripping. = I checked it out and found that while the breaker was tripping it did = not trip immediately after being reset. The fans would run for a while, = usually several minutes to an hour, and then the breaker would trip. = What I found was the power cords to the fans had been secured to the = metal fan mounting brackets with cable ties. The cords were secured = against the flat face of the metal, not an edge, and the fans and the = power outlets were both attached to the same metal brackets. The fans = vibrate slightly but you would think that since everything was mounted = to the same structure there would be hardly any movement. Well, there = isn't much but apparently there was enough that after 7 years the cord = insulation on one of the fans chafed to the point that a bare wire was = making contact with the mounting bracket. The path from the mounting = bracket through the greenhouse structure (all galvanized steel) to = literal earth ground was good enough that it was tripping a 15A breaker. = (The fan normally pulls 1.4A.) After fixing the problem fan I checked = the other one and found that it was also chafing and was very close to = shorting as well. Granted this is not aircraft wiring and it did take 7 years of = continuous operation to fail, but the vibration involved was very slight = and the power cord was being held against a smooth, flat piece of metal. = Think about the harsher conditions, mechanical and environmental, under = the cowls of our airplanes and give some extra thought to simply using a = cable tie to secure wiring to any convenient surface. Just some food for thought for those of us doing our own wiring. Tom Gourley ------=_NextPart_000_002B_01C779D6.D1FBC990 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

Here's something to think about the next time you're using a cable = tie to=20 secure wiring. A couple of days ago my wife told me that the = circuit=20 breaker for the circulating fans in one of her greenhouses was = tripping. I=20 checked it out and found that while the breaker was tripping it did not=20 trip immediately after being reset. The fans would run for a = while,=20 usually several minutes to an hour, and then the breaker would = trip. =20 What I found was the power cords to the fans had been secured to the = metal fan=20 mounting brackets with cable ties. The cords were = secured against the=20 flat face of the metal, not an edge, and the fans and the power outlets = were=20 both attached to the same metal brackets. The fans vibrate = slightly but=20 you would think that since everything was mounted to the same structure = there=20 would be hardly any movement. Well, there isn't much but = apparently there=20 was enough that after 7 years the cord insulation on one of the = fans chafed=20 to the point that a bare wire was making contact with the mounting=20 bracket. The path from the mounting bracket through the greenhouse = structure (all galvanized steel) to literal earth ground was = good=20 enough that it was tripping a 15A breaker. (The fan normally pulls = 1.4A.) After fixing the problem fan I checked the other one and = found that=20 it was also chafing and was very close to shorting as well.

Granted this is not aircraft wiring and it did take 7 years of = continuous=20 operation to fail, but the vibration involved was very slight = and the=20 power cord was being held against a smooth, flat piece of = metal. =20 Think about the harsher conditions, mechanical and = environmental, under the=20 cowls of our airplanes and give some extra thought to simply using a = cable tie=20 to secure wiring to any convenient surface.

Just some food for thought for those of us doing our own = wiring.

Tom Gourley

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