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art(at)zemon.name Guest
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Posted: Tue Aug 29, 2017 5:29 am Post subject: Shield Grounding |
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Folks,
In planning my wiring harness, the manufacturers call for shielded wires to carry the audio signals between the audio panel and the various noise sources. Every sample wiring diagram shows the shield tied to ground at that manufacturer's device so, for instance, the radio manufacturer's sample diagram shows the shield grounded at the radio and the audio panel's sample diagram shows the same shield grounded at the audio panel.
It doesn't matter, right? Can I ground either end of the shield? I do understand that I should not ground both ends.
Thanks,
  -- Art Z.
--
https://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel
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nuckolls.bob(at)aeroelect Guest
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Posted: Tue Aug 29, 2017 5:34 am Post subject: Shield Grounding |
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At 08:27 AM 8/29/2017, you wrote:
Quote: | Folks,
In planning my wiring harness, the manufacturers call for shielded wires to carry the audio signals between the audio panel and the various noise sources. Every sample wiring diagram shows the shield tied to ground at that manufacturer's device so, for instance, the radio manufacturer's sample diagram shows the shield grounded at the radio and the audio panel's sample diagram shows the same shield grounded at the audio panel.
It doesn't matter, right? Can I ground either end of the shield? I do understand that I should not ground both ends. |
Follow the manufacturer's instructions. Grounding
shields at both ends is never 'better' from the
standpoint of breaking the electro-static, noise
coupling mode . . . and sometimes grounding at
both ends can pose new problems.
Bob . . .
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art(at)zemon.name Guest
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Posted: Tue Aug 29, 2017 6:07 am Post subject: Shield Grounding |
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On Tue, Aug 29, 2017 at 8:33 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote: | At 08:27 AM 8/29/2017, you wrote:
Quote: | Folks,
In planning my wiring harness, the manufacturers call for shielded wires to carry the audio signals between the audio panel and the various noise sources. Every sample wiring diagram shows the shield tied to ground at that manufacturer's device so, for instance, the radio manufacturer's sample diagram shows the shield grounded at the radio and the audio panel's sample diagram shows the same shield grounded at the audio panel.
It doesn't matter, right? Can I ground either end of the shield? I do understand that I should not ground both ends. |
 Follow the manufacturer's instructions. Grounding
 shields at both ends is never 'better' from the
 standpoint of breaking the electro-static, noise
 coupling mode . . . and sometimes grounding at
 both ends can pose new problems.
| Â
Bob,
I am confused because the manufacturers have given conflicting info. The audio panel shows all shields grounded at the audio panel (and open at the radios). The radios show the shields grounded at the radios (and open at the audio panel). As far as I can tell, it should not matter. I should be able to ground either end of the shield for any particular wire (and leave the other end open). Right?
  -- Art Z.
--
https://CheerfulCurmudgeon.com/"If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel
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ceengland7(at)gmail.com Guest
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Posted: Tue Aug 29, 2017 7:32 am Post subject: Shield Grounding |
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On 8/29/2017 9:05 AM, Art Zemon wrote:
Quote: |
On Tue, Aug 29, 2017 at 8:33 AM, Robert L. Nuckolls, III <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote:
Quote: | At 08:27 AM 8/29/2017, you wrote:
Quote: | Folks,
In planning my wiring harness, the manufacturers call for shielded wires to carry the audio signals between the audio panel and the various noise sources. Every sample wiring diagram shows the shield tied to ground at that manufacturer's device so, for instance, the radio manufacturer's sample diagram shows the shield grounded at the radio and the audio panel's sample diagram shows the same shield grounded at the audio panel.
It doesn't matter, right? Can I ground either end of the shield? I do understand that I should not ground both ends. |
 Follow the manufacturer's instructions. Grounding
 shields at both ends is never 'better' from the
 standpoint of breaking the electro-static, noise
 coupling mode . . . and sometimes grounding at
 both ends can pose new problems.
| Â
Bob,
I am confused because the manufacturers have given conflicting info. The audio panel shows all shields grounded at the audio panel (and open at the radios). The radios show the shields grounded at the radios (and open at the audio panel). As far as I can tell, it should not matter. I should be able to ground either end of the shield for any particular wire (and leave the other end open). Right?
  -- Art Z.
--
https://CheerfulCurmudgeon.com/ "If I am not for myself, who is for me? And if I am only for myself, what am I? And if not now, when?" Hillel
| Art,
The reason for such confusion with shields is that with most (not all) *data* transmission, the shield is purely a shield and doesn't participate in electron flow (to complete the circuit). But with audio, the shield is often called on to do 'double duty'; providing a shield *and* providing the return path for the electron flow. When that's the case, you must connect the shield at both ends. A quick way to tell is that if you see an audio 'hi', an audio 'lo', *and* a shield (3 lines on the drawing), the shield can be connected at one end. But if you only see an audio 'hi' and a shield, the shield is acting as both the 'lo' and the shield.
An example would be the headphone wire in many mono intercoms. You'll typically see the headphone 'hi' and a shield wire on the drawing. Since almost all intercoms spec that the mic & headphone jacks be isolated from the airframe (ground), if you don't connect the shield at both ends (intercom & jack), you won't have a complete circuit and the headphones won't work.
Charlie
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nuckolls.bob(at)aeroelect Guest
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Posted: Tue Aug 29, 2017 8:03 am Post subject: Shield Grounding |
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Quote: |
Â
Bob,
I am confused because the manufacturers have given conflicting info. The audio panel shows all shields grounded at the audio panel (and open at the radios). The radios show the shields grounded at the radios (and open at the audio panel). As far as I can tell, it should not matter. I should be able to ground either end of the shield for any particular wire (and leave the other end open). Right? |
Correct . . . it never matters at which end it
is grounded . . . but unless the shield is
doubling both ELECTRO-STATIC NOISE COUPLING
combined with a SIGNAL -or- POWER PATH, then
grounding at either end is sufficient and
correct.
If the shield is intended to serve a dual
purpose, then the installation instructions
will be specific as to how BOTH ends of
the shield are managed.
Example: I used to supply an LED annunciator
fixture where is was MECHANICALLY convenient
to use a single shielded wire to make connections
with the back of the LED.
[img]cid:.0[/img]
In this case, the shielding was NOT being
utilized as a noise mitigation feature . . . it
was simply one of the power pathways for the
lamp.
In this case, installation instructions
called out the appropriate treatment . . .
[img]cid:.1[/img]
We have often pondered design features called
out in various documents over the years here
on the list . . . lamenting the fact that we
could not ask the designer to explain the
simple-ideas in physics and/or mechanics that
drove the design.
The simplest thing to do is follow the instructions.
On occasion we have discovered errors in
reasoning/implementation of design goals but
this is very rare.
Bob . . .
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art(at)zemon.name Guest
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Posted: Tue Aug 29, 2017 8:48 am Post subject: Shield Grounding |
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Thank you for the clarification.
   -- Art Z.
Sent from my phone. Please excuse brevity and bizarre typos.
On Aug 29, 2017 11:43 AM, "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com (nuckolls.bob(at)aeroelectric.com)> wrote: Quote: | Quote: |
Â
Bob,
I am confused because the manufacturers have given conflicting info. The audio panel shows all shields grounded at the audio panel (and open at the radios). The radios show the shields grounded at the radios (and open at the audio panel). As far as I can tell, it should not matter. I should be able to ground either end of the shield for any particular wire (and leave the other end open). Right? |
 Correct . . . it never matters at which end it
 is grounded . . . but unless the shield is
 doubling both ELECTRO-STATIC NOISE COUPLING
 combined with a SIGNAL -or- POWER PATH, then
 grounding at either end is sufficient and
 correct.
 If the shield is intended to serve a dual
 purpose, then the installation instructions
 will be specific as to how BOTH ends of
 the shield are managed.
 Example: I used to supply an LED annunciator
 fixture where is was MECHANICALLY convenient
 to use a single shielded wire to make connections
 with the back of the LED.
[img]cid:.0[/img]
 In this case, the shielding was NOT being
 utilized as a noise mitigation feature . . . it
 was simply one of the power pathways for the
 lamp.
 In this case, installation instructions
 called out the appropriate treatment . . .
[img]cid:.1[/img]
Â
 We have often pondered design features called
 out in various documents over the years here
 on the list . . . lamenting the fact that we
 could not ask the designer to explain the
 simple-ideas in physics and/or mechanics that
 drove the design.
 The simplest thing to do is follow the instructions.
 On occasion we have discovered errors in
 reasoning/implementation of design goals but
 this is very rare.
 Bob . . .
|
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