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Shield Grounding

 
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art(at)zemon.name
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PostPosted: Tue Aug 29, 2017 5:29 am    Post subject: Shield Grounding Reply with 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.
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
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PostPosted: Tue Aug 29, 2017 5:34 am    Post subject: Shield Grounding Reply with 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.



Bob . . .


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art(at)zemon.name
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PostPosted: Tue Aug 29, 2017 6:07 am    Post subject: Shield Grounding Reply with 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.

 

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
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PostPosted: Tue Aug 29, 2017 7:32 am    Post subject: Shield Grounding Reply with quote

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.
 

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
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PostPosted: Tue Aug 29, 2017 8:03 am    Post subject: Shield Grounding Reply with 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]

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
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PostPosted: Tue Aug 29, 2017 8:48 am    Post subject: Shield Grounding Reply with quote

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]
 
  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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