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PostPosted: Sat Oct 25, 2014 7:38 am 
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Joined: Sat Apr 02, 2005 12:45 am
Posts: 356
Location: Kentucky
Now this is special...
About a year ago I got into a discussion on here about Romex & MC cable. I did a little research and posted some info HERE... viewtopic.php?f=16&t=18496
and HERE...viewtopic.php?f=16&t=18485

Well, SPEEDSKATER turned me on to Bill Whitlock of Jensen Transformers (PROPS to ya' SPEEDSKATER! Also thanx to Soundman2020 for his help also!). I decided to send email to Bill Whitlock concerning questions I had about things talked about in the posts. Mr. Jenson knows what he's talking about...make NO doubts about that. If ya' NEVER HEARD OF HIM, look him up! You can start here...

"UNDERSTANDING, FINDING, & ELIMINATING GROUND LOOPS IN AUDIO & VIDEO SYSTEMS"
2005 Generic Seminar Template
Instructor - Bill Whitlock
http://www.jensen-transformers.com/an/g ... eminar.pdf

also a newer PowerPoint with notes of his seminar:
http://centralindianaaes.files.wordpres ... s-v1-0.pdf

Basically, Mr. Whitlock's response to my email answers questions concerning the use of Romex cable, MC cable and THHN wiring (THHN wiring in conduit). The chart on page 35 in the link below shows how the different cables/wiring are ranked. You can read the info in this post along with the other two electrical forum posts listed above if necessary. Hopefully you'll get a clearer idea of what "I", "we" were rambling about in all the posts. All page references to my questions below can be found here...

http://centralindianaaes.files.wordpres ... s-v1-0.pdf

Anyway, below is the email I sent that he actually took the time to read and respond to. The letter is in it's entirety excluding non-pertinent info and contact info...
--------------------------------------------------------------------------------------------------------------------------------------------

Hi Stanley,

Thanks for writing. The questions you pose indicate that you’ve read my piece quite thoroughly … thank you. I’ve attached a copy of the 2011 AES paper “Ground Loops: The Rest of the Story” where the comparison graph originally appeared. It contains additional details about the tests and (hopefully) other useful information. You certainly may post my replies in the blog.

All that being said, I’ll happily answer your questions within your original message below (in red text).

Cordially,

Bill Whitlock, Technology Manager

Jensen Transformers, Inc.


From: Stanley
Sent: Friday, October 24, 2014 8:48 AM
To:
Subject: Re-Submitted Question from 10/27/13 for Bill Whitlock

Greetings!
As I stated...I know it's unlikely this email will get to Bill Whitlock, but I'm hoping for an "early Christmas present", so I'm gonna' go for it!

I'll try to be brief...

I'm a "seasoned" musician in the process of trying to build a home recording studio. The seminar notes for "Overview of Audio System Grounding & Interfacing" were forwarded to me to check out. I am NOT an electrician in any shape, form or fashion, so I can't speak in any "technical" terms for what I am talking about in this email. There is a web site with those of us that are trying to build Recording Studios where, let's say "questions" were raised on Romex being better than MC cable. For some of us (who are interested) the answer to my questions may determine the type of wiring that we may use when building our Studios.

Basically, this is it...
On page 35 you have a chart that shows different wiring types and their effect with magnetic induction. The test that were done looked to be using 3 conductor wiring including the MC cable. On the chart, MC cable was slightly better than Romex.

Ok, let me back up...

Page 31...

• Imperfect cancellation magnetically induces voltage over the

length of the nearby safety ground conductor

• Strongly affected by geometry and proximity of wires

• Highest voltages with randomly positioned wires in conduit

• Lower voltages with uniform geometry of Romex®


Page 32... shows the magnetic "null" zone in Romex...


Page 33...

Wires randomly positioned in conduit

produce the worst possible results!

Page 34... shows how the test were done...

As I stated...On page 35 it shows the chart with different types of wiring tested for magnetic induction. The best wiring type was twisted load-neutral (I think that's what the LN means... yes)
I checked with 3 different MC cable manufacturers on their manufacturing process to see if
they "twisted" any of the wiring in their MC cable...
Here is what I wrote in a blog response about this issue...

"Anyway, an update...
Southwire engineering called me back and stated their wire is twisted. He said it's twisted clockwise so many feet then counterclockwise so many feet.

(In pictures of twisting machinery I’ve seen, a rotating platform of wire reels pays out the individual wires as the twisted cable is pulled onto another reel. This “reversal” thing is new to me, but there may be a good reason.)

AFC engineering called me and calculated their "conductor twist" in MC cable is twisted 2.3 to 2.4 times per foot.

So, all 3 cable manufacturers (AFC, Southwire and Encore) stated they do twist their wire in the MC armor. This MAY have something to do with why the Aluminum MC produced the 2nd best results in the test Bill Whitlock conducted."

Ok, here's my questions...
1.) Is the reason MC cable was second best of the wiring types tested due to, or is partially due to the twisting of the wire?

To minimize induction of noise into the ground wire, there are two strategies: 1. Because, at any instant in time they carry the same current in opposite directions, put these two wires as close to each other as possible so their magnetic fields neutralize/cancel each other. Tight twisting is the most practical way to do this; and 2. Put the “victim” ground wire as far away as possible from the current-carrying pair. Because the magnetic fields are very intense close to this pair, the closer the ground wire gets to them, the more critical its exact positioning becomes. Since MC includes the ground (green) wire in the twist, it’s not as good as letting the green wire assume a random position farther from a twisted pair. For the same reason, Romex (type NM) is subject to minor position deviations of the “centered” ground wire simply because it’s so close to the pair. The graph plot for Romex was for a pretty pristine straight length. In typical application, Romex gets bent, which will surely make it fare worse since bending will slightly alter positioning. I may do a follow-up study of this as well as the effect of “stacking” and bundling of Romex in real-world residential wiring.

2.) Would multiple conductor MC cable in steel galvanized armor (let's say 12/4 with ground MC) be worse (as far as magnetic induction and due possibly to the "bad proximity of the wires") than 3 conductor or 4 conductor Romex with it's "uniform geometry"?

I have to confess that I’m unfamiliar with the geometry of these multi-conductor types (I’ve never seen 3 or 4-conductor Romex. But, once you understand the principles I summarized in the previous answer, you can fairly-accurately predict the behavior of any arrangement.

3.) For those who desire to pull THHN wiring through Conduit; Is the best way to set up "twisted" wire in the conduit to have all the grounds in the middle with the hot wrapped around the grounds in one direction and the neutral wrapped around the grounds in the opposite direction?
(If this is wrong, how should the twist be done?)

Nothing that exotic is necessary! As shown in Fig. 4 of the attached paper, the ideal is to pre-twist the current-carrying pairs (typically BLK and WHI) only and then pull the pairs and their ground (GRN) wires into the conduit, letting the ground wires assume random positions. My co-author, Jamie Fox, was the specifying engineer for the AC power at the new Bing Auditorium at Stanford University. He specified twisted L-N pairs for all the AV circuits as well as isolated grounding. He had the L-N pairs pre-twisted by Sourcery Wire & Cable (http://www.sourcery-llc.com/) in Los Angeles. According to reports, the AV systems were remarkably noise-free right from the start with no troubleshooting of noise problems or modifications required. Bear in mind that, if multiple circuits run in the same conduit, all of the circuits must have twisted L-N pairs. Otherwise, one branch circuit can induce noise into the ground of another. And, of course, little or none of this benefit will be realized unless isolated-ground (IG) outlets are used … if J-boxes and metallic conduit are used. In residential settings with no metallic conduit and plastic J-boxes, the system is already “isolated ground” by definition.

4.) Which is better for the inner (THHN) wiring in MC cable...Aluminum armor or Galvanized Steel armor?

You can see from the plots in the attached paper that steel has little effect compared to plastic or aluminum. Steel increases coupling by 4 or 5 dB at frequencies below 10 kHz but decreases coupling above 10 kHz. The change above 10 kHz is likely due to eddy current effects – both aluminum and steel would likely do this. More subtle details to study!

5.) "If" you respond...Hmmmmmmm...
Scratch that...I'm "gonna" BELIEVE...
WHEN you respond, can I put your response on the Studio Blog?

Yes, I just hope folks will appreciate that this is real science, not audiophile magical thinking, and that I have little to gain from making the information public. Seems to me that some enterprising electricians could specialize in low-noise wiring for AV systems – learning this technique as well as using isolated grounding, separately-derived power, etc. as discussed in the Middle-Atlantic white paper, which I helped write, listed as a reference in the Whitlock-Fox (attached) paper.

Well, that's it...
I'll let you go now with a "Thanx" in advance!
Sincerely,
Stanley
--------------------------------------------------------------------------------------------------------------------------------------------
Well, that's the end of the email. A big thanx again to Bill Whitlock on answering the questions and giving a clearer picture of Romex compared to MC cable and THHN wiring (THHN wiring in conduit).

_________________
Take Care and GOD Bless
Stan


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PostPosted: Sat Nov 01, 2014 6:38 am 
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Joined: Thu Aug 21, 2008 10:17 am
Posts: 11984
Location: Santiago, Chile
Very good advice! Thanks for the update, Stan. Very interesting.


- Stuart -

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