Grounding and Shielding. A little light reading

[Kingrex]

This is some of the stuff I read. This is a new book to me. I need to understand the implications of shielding. A specialized professional in recording studio work pretty consistently uses shielded cable in his projects. A mentor of mine got over technical for me explaining why a shield is a negative influence with high end audio. That conversation lead me to purchase this book to better understand what he was saying.

In the preface, the author Ralph Morrison nailed one of my founding beliefs about wiring, validating for me, how I have been approaching wiring.

 

[Alrainbow]

Great stuff rex ,
explain a little
his comment on space of conductors makes sense
but elaborate a bit please

there are many types of shielding for sure

 

[MarkusBarkus]

...man there is such a strong set of opinions on both sides: to shield or not to shield. I think some of the desire to shield cables is practical: that it is very difficult to keep conductors apart from each other in the real world. Or the hifi world either.

 

[microstrip]

Nice to know of someone else in WBF that appreciates this great book - we have posted on it several times before along years. But the more you read it the better you will understand that it is not possible to have a an unique grounding practice for high-end systems - probably most manufacturers have not read the book and their gear is not predicable in terms of grounding and RF noise.

The introduction wisely refers that the frequency range of RF interference and noise has widened by three orders of magnitude in twenty years and most of what was adequate in the past century is not anymore. Going in the new edition needs a deeper background in physics than my old student version of this book!

 

[Kingrex]

Absolutely right Markus. There are 2 very entrenched camps. I became spun up on the subject as I have a current project in a high $$$ home. In order to feed the MBL Extremes, I have to get signal cables for the woofer, power for the woofers and speaker cables for the main speakers across a ceiling inside false beams. Its close to 60 feet of parallel cables.

This caused me to look at metal clad (MC) cable for the power wires. I have watched and read quite a bit on the subject in the last year. But I have nerver gotten cozy with MC cable. Look at the distribution of electrons in orbit around a conductor in figure 1.2. What is going on with that field when you put a case of magnetic steel, aluminum or copper around the wire. What have I done to the electron field. What impact has this on the magnetic field. I don't know yet. I just started this book last night. But I have been warned by well known people the affect is not desirable.

At some point I am going to have to do what I usually end up doing. Taking say a 50 foot run of MC, twisted THHN solid and stranded and listen. Before I do that I want a better engineering understanding of what I am looking at. It will aid in building better test scenario and how to properly measure the results.

 

[Kingrex]

Nice to know of someone else in WBF that appreciates this great book - we have posted on it several times before along years. But the more you read it the better you will understand that it is not possible to have a an unique grounding practice for high-end systems - probably most manufacturers have not read the book and their gear is not predicable in terms of grounding and RF noise.

The introduction wisely refers that the frequency range of RF interference and noise has widened by three orders of magnitude in twenty years and most of what was adequate in the past century is not anymore. Going in the new edition needs a deeper background in physics than my old student version of this book!

I will have to read it a couple times, then try and apply some of the formula.

I found it interesting they note the sequence you stack grounds on the stud matters. I have also believed this to be true and have an order I follow. It can be very audible if a panel is made up with no thought for performance., just to meet code. Unfortunately some distribution gear is built wrong. So many main disconnects now tack a stud to the can forcing any strat voltage and noise to travel through a lug, through a screw, across a metal can, through another screw, into another lug, to then get into the main grounding electrode. Its just wrong. You don't want your can to be a conducting piece of metal. Morrison is looking at a circuit board and states, "the connection should be arranged so that ground current does not flow in the ground plane on the board". This is missed in most every service I look at.

 

[MarkusBarkus]

@Kingrex I seem to recall you preferred solid THHN in the past, is that correct? About a week before one of our forum exchanges here, I had just run 35' of twisted #10 THHN in steel flex. Ugh. I thought stranded would be better and easier, although I did not have any hard-data on that vs. solid.

I am not finding any substantial data on the topic, but since running in steel, I have wondered whether aluminum might be better. I was going for what I expected to be better shielding properties, but perhaps a non-ferrous material would be better?

In any case, what does seem to be agreed is that one should twist the THHN before the pull to avoid any "transformer-like" effects in the melange of wire. I seem to recall you twist em up.

I live in the NE US, urban location, with a *lot* of RF and EMI soup around. Harris L3 (formerly Harris RF) is a couple of blocks away. They have antenna arrays that are very impressive. Always driving humvees around testing comms.

Although I am not able to measure all this radiation (although it is possible with the right tools), I can see it exists, so I always ran shielded cables for network and general power and signal.

Until recently...6-8 months. I was re-doing a few things, so I tested some unshielded cable. I couldn't hear a difference, for what that's worth.

I am embarrassed to say I *still* have not run that #6 copper tri-plex for a new dedicated line to test against that #10 in FMC. Ugh. Gonna be a PITA. Graph may be of general interest. Cheers...

 

[Alrainbow]

I wonder if running the equipment gnd alone matters
i always like romex for this reason
as for grouping man I can see this being issues
shielding is not grounding but both effect each other

Soares Book on Grounding and Bonding,... book by International Inspectors

the first book I read on NEC code
I would think this and rex book is needed

 

[Kingrex]

I have read Soares and I have read the Bill Whitlock papers. They are in my white paper files.
I like solid. I have had exceptionally good results with stranded too. I can grain orient the solid and hear the direction so I use it.

The question is, what are you trying to shield against.
Steel shield at lower frequency. Its good for say line voltages.
Aluminum shields better for RF frequency.
Both of these are not really good shields. Again, copper is king. Copper is an excellent shield.
But then again, are we talking a braid or a foil, and how thick are the walls.

Then the question is, did the noise already get in through the utility????? So what is that shield doing.
How do you get rid of the noise on the shield.

Lets say I put a whole house transformer in the basement below your listening room, how much RF gets back in through the 10 to 40 feet from the transformer to the duplex. How much got in through the power cables and interconnect. How much got in through the actual equipment itself. I know a guy who had a phono cartridge that was coupling with RF. I have another friend with a phono preamp that when used plays radio stations for him. I had a tube preamp that did the same thing. The thing about noise it that it does not attaches itself to everything in equal measure. Where and to what degree it enters, and the damage it does is not something I think anyone can measure. The variables are too great.

Here is a shielding story. I got the idea wires in close proximity in my panel were injecting noise into my critical audio power. I sleeved a critical bonding jumper that manages all my audio neutrals and grounds in an piece of aluminum MC jacket. I pulled the conductors out of the MC and sleeved my bond wire into. I wrapped the case in a bare silver wire and bonded it to my primary ground stud. What a failure that was. That shield shut down all life in my audio. 28" or so of shield on the primary neutral/ground and I ruined my audio. As soon as I pulled the shield off and left the wire packed in amoungst the other conductors in the panel, my audio jumped back to normal performance. That is part of why I have never pursued MC cable as a branch run in my audio systems.