Shielding/Screening

[Ausman]

Hi all,

in response to Hotwires asking about Aussie naming conventions re "screening", I looked it up on Wiki just to learn different names and see if I was being a goose.  I found this sentence:

{{{ The best way to wire shielded cables for screening is to ground the shield at both ends of the cable.^[1] Traditionally there existed a rule of thumb to ground the shield at one end only to avoid ground loops. }}}  

The reference note for [1] is this page:   http://www.compliance-club.com/archive/old_archive/020514.htm

I would like opinions on this please for our applications.   I am traditional.....always only at one end.  Yet can change if it is thought best.

cheers,

Aus

[hotwires]

Term screening in relation to shielded cable is new to me. Not sure what "being a goose" means either.

[Ausman]

"being a goose" was my terminology for me perhaps always using a wrong name for something, and being incorrect/silly/outoftouch/old/dumbo/yougettheidea.

But screened and shielded appear to be synonyms.  I actually had somewhere in my brain that shielded was braided stuff, and screened was only foil with a drain wire.

But the main point is what is best practice?  In many bits of literature from major multi-nationals I have read about earthing both ends of a 485 line, for example.  But then you read from other major players to not do this, as it defeats the entire purpose of protecting the inner cables.  Or protecting things outside the cable if it is on VFDs etc.

Sticking with the one end only method has always given me reliable connections b/n anything I've used it on.  But I'm always open to suggestions.

A bit like politics, or the media....who do you believe?!!

cheers,

Aus

[Joe Tauser]

JT-

Don't mind us seppos and our funny tawkin'.

Joe T.

[John_R]

Screen/Shield, always been the same thing in my mind, although from a broader perspective, shielding may refer to the braid/foil/drain wire on a cable, while screening may be thought of as something in a bigger sense, like a metal (screen) partition between noisy parts of a panel and noise sensitive parts.....

I've been doing industrial control for 30 years, and was always lead to believe "one end" grounding to be proper in this field.

But, before that, I worked in the audio electronics field, and the proper method was to ground both ends of the shield, but you also did your best to maintain a "star ground" topology to eliminate potential ground loops.....

just my 2cents.....

Disclaimer.... at least in my part of the world, I realize Aus and others have words and meanings that us funny tawkers don't get........

JohnR

Edited August 28, 2017 by JohnR
clarification

[Davenj]

Shielding is the common term.  Screening is not used that often.  Shielding pertains to both cables and enclosures.  Grounding the shield at one end is ok if your only going  to see low field levels (high field levels both ends).  The shield termination should be as short as possible.  At high frequencies a longer length  termination will be an open.  Enclosures shielding refers to conductive gaskets, apertures, windows, etc. 

Ex-Electromagnetic Interference 30yrs

[lawry]

On 8/28/2017 at 11:23 PM, JohnR said:

Screen/Shield, always been the same thing in my mind, although from a broader perspective, shielding may refer to the braid/foil/drain wire on a cable, while screening may be thought of as something in a bigger sense, like a metal (screen) partition between noisy parts of a panel and noise sensitive parts.....

I've been doing industrial control for 30 years, and was always lead to believe "one end" grounding to be proper in this field.

But, before that, I worked in the audio electronics field, and the proper method was to ground both ends of the shield, but you also did your best to maintain a "star ground" topology to eliminate potential ground loops.....

just my 2cents.....

Disclaimer.... at least in my part of the world, I realize Aus and others have words and meanings that us funny tawkers don't get........

JohnR

In audio electronics, this was necessary, as the shield would usually be connected to the analog ground and would not be necessarily earthed. Whereas in industrial applications, the shield would best be earthed at one (preferably the source) end and have no connection to any Vcc grounds.