[Speedskater]

I thank that Dave's Hot and Neutral wires were 10AWG twisted together (one turn per foot).  The Safety Ground wire was  8AWG touching the others but not twisted. The Code only allows one Ground, Neutral setup depending on if it's a Main or Sub panel.

[dmatt]

This is a timely thread for me since we will be upgrading the power for AV to five dedicated 20A lines.

To be able to spec what I'd like to our electrician, I have been reading the following sources: 
Middle Atlantic Products white paper http://www.middleatlantic.com/power.htm
Tech articles from the Equitech site http://www.equitech.com/articles/articles.html
Info from the Controlled Power Company site http://www.controlledpwr.com/Ultra-K_K-Rated_Isolation_Transformer.html
Info from Arthur Kelm's site http://www.ground1.com/about.htm
And posts on Agon http://forum.audiogon.com/cgi-bin/fr.pl?vaslt&1250107418&openfrom&7&4#7 and WBF http://www.whatsbestforum.com/forumdisplay.php?206-Arthur-S.-Kelm-On-Clean-Power

Most of the info is consistent (as you'd hope), and is echoed in this thread.

I do have a question from dBe's earlier post

When I installed my dedicated lines, I used Siemens 20A circuit breakers and ran 10ga wire twisted @ 1TPF with a parallel run of 8ga for the ground.  The ground IS NOT twisted in the H/N pair.  Low impedance ground paths are essential where noise reduction devices are used at the circuit terminus.

This is the preferred approach as well by a couple of the sources I listed -- don't twist the ground with the hot and neutral

However the Middle Atlantic white paper, in recommending Metal Clad (MC) and Armor Clad for Healthcare Facilities (AC-HCF), suggests that twisting the insulated ground wire along with the hot and neutral will reduce Ground Voltage Induction (GVI):  "Another benefit is the constant symmetry of the phase conductors with respect to the grounding conductor which greatly reduces voltage induction on the grounding wire. (NEC article: 330)" ... "This symmetry cancels almost all the magnetic field in this one grounding conductor"

Elsewhere they say that for a ground that isn't twisted with the phase conductors that:  "The conductors are twisted, but the average proximity of the hot conductor and the neutral conductor with respect to the grounding conductor is not equal. Under load, this will induce a voltage along the length of the ground wire."

Seems to make sense, right?

But they go on to say later that "The most effective way to reduce GVI is to twist the phase conductors together and pull through a conduit with a straight ground wire. This may be time consuming and impractical, but for critical situations where millivolts matter, this may be the best solution."

It seems like they are contradicting themselves.  Am I missing something?

Does this make sense to you guys?  I'm just treading water here.

Thanks.

DM

[dBe]

I thank that Dave's Hot and Neutral wires were 10AWG twisted together (one turn per foot).  The Safety Ground wire was  8AWG touching the others but not twisted. The Code only allows one Ground, Neutral setup depending on if it's a Main or Sub panel.

Exactly.  The twisted pair runs parallel to the ground to resist eddy currents and mutual induction between the neutral and the ground.  My earth ground consists of a three ground rod string located near a downspout and close to where the spronklers pool.  I live in an arid climate and good grounding is essential.

Dave

[Speedskater]

"DM" you missed two of the best papers:

http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

http://www.jensen-transformers.com/an/generic%20seminar.pdf

Middle Atlantic recently changed their position on AC-HCF  Armor Clad. It seems that there are no manufacturing standards for wire geometry.

[dmatt]

Thanks for the links, Speedskater.

To make sure I understand your post, are you saying that there was no guarantee that the wires in the AC-HCF Armor Clad would be twisted the way Middle Atlantic assumed they were (maybe no twist at all), so they dropped their recommendation?

David

[Speedskater]

Something like that.  See:

http://www.middleatlantic.com/pdf/Power%20Paper%20Addendum.pdf

[dBe]

Seldom do we see a single (rather than dual) 15 Amp receptacle.
Maybe the only places are for a recessed wall mount clock outlet or some permanent kitchen appliances .

I've seen people install 15A single receptacles on dedicted 20A circuits for monoblock applications.  This is definitely a no-no!   

I would not recommend residential grade 15A duplex outlets for use on a 20A circuit.  The cheapies are really borderline in conductor cross section and contact pressure to do the job.  Most of the electrical inspectors in the Albuquerque Metro area would flag a 15A duplex on a 20A circuit as a matter of course.  While the 15A unit may meet the letter of the spec it is just kind of iffy in application.  A 15A specification grade is an entirely different matter.  Like you said, the 15A and 20A are internally identical.

It is just those freakin' $0.99 15A residential grade receptacles that give me the willies when people try to use them in high current audio applications... or ANY application for that matter.  I believe in a healthy safety margin.  Then again, I overbuild everything.   

Dave

[tabrink]

 I have standardized on the L-5 20r &p.

[dmatt]

Something like that.  See:

http://www.middleatlantic.com/pdf/Power%20Paper%20Addendum.pdf

Thanks for the link, Speedskater.  For some reason my computer wasn't showing the webpage that had the addendum on it.

To all of you "in the know";
Should the ground be twisted with the hot and neutral to maintain symmetry and prevent inducing voltage in the ground wire (Middle Atlantic)?

Or should the ground be straight (not twisted) to resist eddy currents and mutual induction between the neutral and ground (as Dave points out, along with Arthur Kelm, etc.)? 

Or does it matter as long as the hot and neutral are twisted?  Bill Whitlock's paper just states that the technical ground should be "routed back to the electrical panel alongside the white and black circuit conductors to keep inductance low." and doesn't go into details.  Jim Brown's paper talks about running "the phase and neutral conductors for each power circuit as twisted pairs within their conduit so that the radiated magnetic field cancels." and "Additional magnetic field rejection will be achieved if audio circuits are twisted pairs."  but that is as it relates induction between power lines and signal lines.

I'm just trying to reconcile what appears to me to be two different approaches before I fire up my drill and twist wires for my electrician.  If it is six of one and half dozen of another, that is a fine answer too.

David

[dBe]

Thanks for the link, Speedskater.  For some reason my computer wasn't showing the webpage that had the addendum on it.

To all of you "in the know";
Should the ground be twisted with the hot and neutral to maintain symmetry and prevent inducing voltage in the ground wire (Middle Atlantic)?

Or should the ground be straight (not twisted) to resist eddy currents and mutual induction between the neutral and ground (as Dave points out, along with Arthur Kelm, etc.)? 

Or does it matter as long as the hot and neutral are twisted?  Bill Whitlock's paper just states that the technical ground should be "routed back to the electrical panel alongside the white and black circuit conductors to keep inductance low." and doesn't go into details.  Jim Brown's paper talks about running "the phase and neutral conductors for each power circuit as twisted pairs within their conduit so that the radiated magnetic field cancels." and "Additional magnetic field rejection will be achieved if audio circuits are twisted pairs."  but that is as it relates induction between power lines and signal lines.

I'm just trying to reconcile what appears to me to be two different approaches before I fire up my drill and twist wires for my electrician.  If it is six of one and half dozen of another, that is a fine answer too.

David

I personally believe that the capacitance of the H/N twisted pair is a good thing in power cables for HF attenuation.  That is why I do it that way.  There are differences of opinion concerning the N/G parallel lay in a twisted triad. I personally feel that the parallel run twisted H/N pair-ground is the best compromise.

My .02

Dave 

[dmatt]

Thanks, Dave.  That helps.

Is there a downside to more twists than one per foot? 

I have been doing some digging in the Belden online catalog and they have 10 AWG twisted pairs and triples -- both stranded and solid wire.  But no info on how many twists per foot; I am guessing it may be more than 1TPF.  Assuming the Belden is applicable for mains voltage and would pass code, it would be easier to run 50ft of that through six conduits than twist wires myself.

David

[dBe]

Thanks, Dave.  That helps.

Is there a downside to more twists than one per foot? 

I have been doing some digging in the Belden online catalog and they have 10 AWG twisted pairs and triples -- both stranded and solid wire.  But no info on how many twists per foot; I am guessing it may be more than 1TPF.  Assuming the Belden is applicable for mains voltage and would pass code, it would be easier to run 50ft of that through six conduits than twist wires myself.

David

David, I don't think that there would be a downside, but I haven't really done any testing so it is just a hunch.  I know that less than that is not a particularly good idea.  We live in a region where there is literally a billion watts of RF floating around with all of the antennae on Sandia, Crest, Kirtland AFB, Sandia National Labs (a lot of ULF there, too) and all of the repeaters around.  Better than that is all of the telemetry and switching data transmitted > 100KHz on the power lines.  Just sucks here.   

As long as the Belden is the UL approved PVC/nylon THHN I don'r see a problem with it.  They make good wire.

Dave

[Speedskater]

I would twist the Hot and Neutral but not the Safety Ground for two reasons:
1] Whitlock writes about how the Hot, Neutral and Safety Ground become a parasitic transformer (see seminar paper, sec. 1.3, page 9). So if we twist only the Hot and Neutral we reduce this parasitic action.
2] The main purpose of the Safety Ground is guess what "safety". Both lightning and power line surges have a large high frequency component. At this high frequencies the self-inductance or the wire is more important than the resistance. A straight wire has less of this self-inductance than a coiled wire.

On turns per foot:
One turn per foot (TPF) is way better than no turns at all!
Two TPF is a little better than one TPF and three is a little better than two.  But it's a case of diminishing returns. The more turns the more difficult the instillation and the longer the wires become.

Some where in the papers of Jim Brown or H. Ott is a chart on frequencies and twists.

[Speedskater]

On a similar note, Those building a home theater or listening room, should also twist the Romex (NM) power cables and the in-wall zip type speaker cables. Maybe in opposite directions and different TPF.

[dmatt]

Dave and Speedskater,

Thank you very much.  You guys are great.  Speedskater, thanks for pointing out the section of Whitlock's seminar I overlooked.  I did skim both docs for info but I guess I'm guilty of not reading carefully.

Speaking of Whitlock, I found an AES paper he and Jamie Fox presented at the AES Convention last November entitled, Ground Loops:  The Rest of the Story.  I purchased it from the AES library and will give it a read.  It appears to carry on the stuff started in his earlier papers.  From the AES site:

"The mechanisms that enable so-called ground loops to cause well-known hum, buzz, and other audio system noise problems are well known. But what causes power-line related currents to flow in signal cables in the first place? This paper explains how magnetic induction in ordinary premises AC wiring creates the small voltage differences normally found among system ground connections, even if “isolated” or “technical” grounding is used. The theoretical basis is explored, experimental data shown, and an actual case history related. Little has been written about this “elephant in the room” topic in engineering literature and apparently none in the context of audio or video systems. It is shown that simply twisting L-N pairs in the premises wiring can profoundly reduce system noise problems."

Cool stuff.

David

 

[Speedskater]

A couple of years ago, I made a list of more than 50 Whitlock papers and magazine articles that were available on the web. But over time most of the links have broken.

I still have that XLS spreadsheet with over 100 papers and articles on AC power, balanced circuits or interconnects.