Terminating Shielded twisted pair

This page has quite a good discussion of terminating the shields of audio cables:

One thing I like is that they actually measured it, rather than just pontificating.

It might not be so applicable in places where mains sockets have historically lacked an earth pin.

Gosh, an atricle about grounding and shielding that makes sense. That's rare.

For something to make sense to John Larkin it has to be very clearly written and can't assume much background knowledge. Most texts are aimed at a more sophisticated audience. This one isn't - there's no mention of common mode chokes.

Whilst the possibility of using these had occurred to me, for a large studio installation it would be impractical to fit each cable with a common-mode choke able to take more than a fraction of a volt at 50Hz without saturating the core. Such a choke might easily weigh a kilogram, if made well enough to be usable for e.g. microphone signals (e.g. by winding the screened cable several times through an iron or mumetal core). Perhaps this was obvious to the authors and they assumed it as background knowledge.

Pickup by a ground loop is unlikely to be 'more than a fraction of a volt'. Neither twisted shielded pair nor coaxial cable does much inductive pickup except for ground loops.

Unfortunately, the article doesn't deal with different mains wiring conventions and how to avoid ground potential differences a.k.a "ground loops" in the first place.

Neither does it address the problems with PE (Protective Earth) network pollution due to mains filter Y capacitors, which feeds some switching mode power supply noise currents into PE. which will cause voltage differences and thus some currents in the signal cable shields. For this reason, a completely separate TE Technical Earth (now officially FE Functional Earth) network is sometimes used. When cable shields are connected to TE, there should ne no current in the TE network and cable shields.

The TE network is connected to the PE in exactly one point at the mains entry point (in which it is usually also connected to the Neutral in TN-S/TN-C_S mains wiring conventions).

The entire world needs a single-point signal ground. It should be at

0/0 lat/longitude, or in Greenwich.

Wiring up to that signal-ground point properly might, just possibly, require more room-temperature superconductor cable than one can acquire at Radio Shack these days.

Didn't you know that they used the ground potential of Sevre outside Paris as the standard potential :-). Unfortunately it became too polluted (solar storms, SMPS noise etc) to be of any use anymore.

The standard horse used to live in Sevre, which was used to define one horse power. Unfortunately the horse got old and finally died, so it has been a more and more common to quote car power in kW instead HP.

Sevre also contained the standard meter prototype as well as the standard kilogram prototype, but also these are now defined without physical prototypes.

Yes, and zero-inductance cable. Where can you get that?

Jeroen Belleman

0 degrees, 0 degrees has higher conductivity, probably. Plus the EU could use a base there to help harmonize the historical definititions of the metre by shaving the Earth so as to make the Paris half-meridian exactly 10 million metres. That's the sort of project that would appeal to the French, for sure. ;)

Cheers

Phil Hobbs

That _is_ a problem. Deliveries from Tumbolia have been badly delayed by COVID-related shipping problems.

The triple-shielded zero-inductance RTS cable is in particularly short supply... and as we all know, you just can't trust the eBay sellers who assure you that they're shipping the genuine article. Like as not, they'll take your money, send you a roll of damp twine, and then close their eBay store and open another one.

I don't think the French will appreciate shaving the earth along the Paris meridian, but they'll be happy to do so for the one running through London.

Jeroen Belleman

Might a cable made with bismuth(antimagnetic!) be a solution?

Have you been to Greenwich? The old observatory is cool, and there's a line outside where you can (presumably) stand and straddle the hemispheres.

And a foot tunnel under the Thames.

0 N / 0 E is in the middle of Gulf of Guinea outside of Africa. Would that reference point be on the surface in a ship or at the bottom of the ocean ?

A pretty big copper rod should do.

I always ground everything as often as I can. PCB ground planes to spacers to the metal box. All the connector shells. Cable shields. Displays. Knob bushings. Optical gadget cases. Heat sinks. Everything.

Saves a lot of thinking.

Whichever comes first.

That's the point--sea water is usually a better conductor than dirt. (Omitting smileys seems dangerous round here.) ;) ;) ;)

Cheers

Phil Hobbs