X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 18 Dec 2013 20:41:50 -0500 Message-ID: X-Original-Return-Path: Received: from mail-qe0-f54.google.com ([209.85.128.54] verified) by logan.com (CommuniGate Pro SMTP 6.0.7) with ESMTPS id 6644504 for lml@lancaironline.net; Wed, 18 Dec 2013 16:28:08 -0500 Received-SPF: pass receiver=logan.com; client-ip=209.85.128.54; envelope-from=dave.saylor.aircrafters@gmail.com Received: by mail-qe0-f54.google.com with SMTP id cy11so231327qeb.13 for ; Wed, 18 Dec 2013 13:27:35 -0800 (PST) X-Received: by 10.224.34.71 with SMTP id k7mr34349777qad.15.1387402054973; Wed, 18 Dec 2013 13:27:34 -0800 (PST) MIME-Version: 1.0 Received: by 10.97.2.233 with HTTP; Wed, 18 Dec 2013 13:26:54 -0800 (PST) In-Reply-To: References: From: Dave Saylor X-Original-Date: Wed, 18 Dec 2013 13:26:54 -0800 X-Original-Message-ID: Subject: Re: [LML] Shielded Wiring Best Practices X-Original-To: Lancair Mailing List Content-Type: multipart/alternative; boundary=001a11c291e6a5bfbb04edd5b6b5 --001a11c291e6a5bfbb04edd5b6b5 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable For terminating shields, the basic principle is to route any stray voltage to a single point, ideally the main avionics ground point. I usually see most manufacturers call out to ground only one end of the shield. The other end remains open, which makes sense if I think about the previous statement--only one path to ground so fewer opportunities for ground loops. That said, I don't really think it's necessary to use TSP for power feeds through breakers, switches, and other DC devices. It wouldn't hurt for the things you mentioned but if you shielded every DC wire you'd have a lot of extra complexity, and a lot more room for error and for a stray strand to mess up your day. If you really want to go through all that effort, make a jumper from the shield, around the switch, back to the shield. That covers the great majority of wire length without having to use a metal box for the components. Lots of work and maybe not much reward. I'd be more likely to of course shield the audio lines, then serial wires and anything else with an audible frequency. That way you're taking the biggest swipe at keeping the audio quiet. If you haven't used solder sleeves, they're a great way to terminate shields and install a jumper. Quick, clean, cheap, small, easy. Also, get metallic DB housings if your device doesn't provide them. Lots of things seem to come with plastic housings these days. Dave Saylor 831-750-0284 CL On Wed, Dec 18, 2013 at 12:45 PM, Valin & Allyson Thorn < thorn@starflight.aero> wrote: > Hey LML gang, > > > > We=E2=80=99re not sure how best to implement shielded wiring out to compo= nents in > our airplane. We=E2=80=99re wanting to ensure we don=E2=80=99t have a bu= nch of > electromagnetic interference (EMI) that might mess with sensitive > components like the ADHARS magnetometer. Examples of EMI sources would > be power lines running to motors (flaps, hydraulic pump, AC fans, AC > compressor) and components with rapidly changing electrical current (stro= be > lights, HID lights). > > > > My understanding is that Twisted Shielded Pair (TSP) cables are ideal for > DC power transmission since the magnetic fields mostly cancel each other > out and shield absorbs what=E2=80=99s left. I=E2=80=99m not sure, though= , how best to > implement their termination at the ground/negative bus and positive bus > -- at the switch in most cases, then line running to the circuit breakers > or fuse. At some point, the separate conductors have to leave the > shielded jacket and run to these separate connections which seems to defe= at > the benefits of the TSP. > > > > Considering this, would it be better to use two individually shielded > Tefzel jacketed wires and twist them together for the part of the path > where they run together and then they each have their individual shields = as > they separate and run to their connections? > > > > What are the best practices on actually implementing shielded wiring for > power and signal transmission in our airplanes=E2=80=A6? > > > > Thanks, > > > > Valin Thorn > > Legacy Project > > Boulder, Colorado > > > > > > > > > --001a11c291e6a5bfbb04edd5b6b5 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
For= terminating shields, the basic principle is to route any stray voltage to = a single point, ideally the main avionics ground point. =C2=A0I usually see= most manufacturers call out to ground only one end of the shield. =C2=A0Th= e other end remains open, which makes sense if I think about the previous s= tatement--only one path to ground so fewer opportunities for ground loops.<= /div>

That said, I don't really = think it's necessary to use TSP for power feeds through breakers, switc= hes, and other DC devices. =C2=A0It wouldn't hurt for the things you me= ntioned but if you shielded every DC wire you'd have a lot of extra com= plexity, and a lot more room for error and for a stray strand to mess up yo= ur day. =C2=A0If you really want to go through all that effort, make a jump= er from the shield, around the switch, back to the shield. =C2=A0That cover= s the great majority of wire length without having to use a metal box for t= he components. =C2=A0Lots of work and maybe not much reward. =C2=A0I'd = be more likely to of course shield the audio lines, then serial wires and a= nything else with an audible frequency. =C2=A0That way you're taking th= e biggest swipe at keeping the audio quiet.

If you haven't used solder= sleeves, they're a great way to terminate shields and install a jumper= . =C2=A0Quick, clean, cheap, small, easy.

Also, get metallic DB housings= if your device doesn't provide them. =C2=A0Lots of things seem to come= with plastic housings these days.

Dave Saylor
831-= 750-0284 CL


On Wed, Dec 18, 2013 at 12:45 PM, Valin = & Allyson Thorn <thorn@starflight.aero> wrote:

Hey LML gang,

=C2=A0

We=E2=80=99re not sure how= best to implement shielded wiring out to components in our airplane.= =C2=A0 We=E2=80=99re wanting to ensure we don=E2=80=99t have a bunch= of electromagnetic interference (EMI) that might mess with sensitive compo= nents like the ADHARS magnetometer.=C2=A0 Examples of EMI sour= ces would be power lines running to motors (flaps, hydraulic pump, AC fans,= AC compressor) and components with rapidly changing electrical current (st= robe lights, HID lights).

=C2=A0

My un= derstanding is that Twisted Shielded Pair (TSP) cables are ideal for DC pow= er transmission since the magnetic fields mostly cancel each other out and = shield absorbs what=E2=80=99s left.=C2=A0 I=E2=80=99m not sure= , though, how best to implement their termination at the ground/negative bu= s=C2=A0 and positive bus -- at the switch in most cases, then = line running to the circuit breakers or fuse.=C2=A0 At some po= int, the separate conductors have to leave the shielded jacket and run to t= hese separate connections which seems to defeat the benefits of the TSP.=

=C2=A0

Consi= dering this, would it be better to use two individually shielded Tefz= el jacketed wires and twist them together for the part of the path w= here they run together and then they each have their individual shields as = they separate and run to their connections?

=C2=A0

What = are the best practices on actually implementing shielded wiring for power a= nd signal transmission in our airplanes=E2=80=A6?

=C2=A0

Thank= s,

=C2=A0

Valin= Thorn

Legacy Project<= /u>

Boulder, Colorado

=C2=A0

=C2=A0

=C2=A0

=C2=A0


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