Dedicated power circuits

Old White Paper. Middle Atlantic Products, Inc.

https://cdn.cableorganizer.com/old-images/midatlantic/PowerSolutions-middle-atlantic.pdf

( Rev 2b 8/7/2007 )

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Newer white Paper. Middle Atlantic Products, Inc.

Integrating Electronic Equipment and Power into Rack ...

( Rev 4b 2002-2010 )

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Page 12:

Integrating Electronic Equipment and Power into Rack Enclosures © 2002-2010 Middle Atlantic Products, Inc.

AC Power Wiring Types (cont’d)

Metal Clad (MC) is manufactured in both steel and aluminum with twisted conductors that help reduce AC magnetic fields. Although the steel jacket helps reduce AC magnetic fields, the twisting of conductors has the greatest effect on reducing these fields. 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)

Two conductor plus 1 ground MC (Metal Clad) is a good choice for Non-Isolated Ground A/V systems. MC cable contains a safety grounding conductor (wire). The three conductors in the MC cable (Line, Neutral and Ground) are uniformly twisted, reducing both induced voltages on the ground wire and radiated AC magnetic fields. The NEC article 250.118 (10)a prohibits the use of this cable for isolated ground circuits because the metal jacket is not considered a grounding conductor, and it is not rated for fault current.

Two Conductor plus 2 ground MC (Metal Clad) may be used in an Isolated Ground installation, because the cable contains two grounding conductors (one for safety ground and one for isolated ground).

The conductors are twisted, but the average proximity of the hot conductor and the neutral conductor with respect to the isolated grounding conductor is not equal. Under load, this will induce a voltage along the length of the isolated ground wire, partially defeating the intent of isolation (see Ground Voltage Induction section of this paper).

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Again:

Two conductor plus 1 ground MC (Metal Clad) is a good choice for Non-Isolated Ground A/V systems. MC cable contains a safety
grounding conductor (wire). The three conductors in the MC cable (Line, Neutral and Ground) are uniformly twisted, reducing both
induced voltages on the ground wire and radiated AC magnetic fields.

Read page 13. Look at the chart on page 13.

Note the far right hand side of the chart.

Arrow pointing up, Worst. Note where NM Cable is on the chart. Look at the numbers...

Arrow pointing down, BEST. Note where MC Cable is on the chart. Look at the numbers...

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Note the picture of the test board where the NM cable, (Romex) is fastened in place. Note the piece of cable is laying flat on the board. No twists, laying flat. Do you think when an electrician installs, say, 50ft to 75ft he takes care to make sure there is not any twists in the cable? Not hardly.

Look at the picture of Romex, NM cable, on page 32.

An Overview of Audio System Grounding and Interfacing

Note:

There is a magnetic “null zone” exactly midway between line conductors

What happens when the cable has twists ever so often along it’s entire length from the electrical panel to the wall outlet box? Do yo think the “null zone” exactly midway between line conductors is altered in any way?

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An Overview of Audio System Grounding and Interfacing

Read pages 31 thru 36.

Look at the chart on page 35. Note Aluminum MC cable beats out NM cable.

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FWIW, When I wired my dedicated 2 channel audio room in 2011 I ran two 75ft each of 10/2 NM cable. I followed best practices for the installation. 100% no twists? I doubt it.

My system is dead quiet...

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I have been in a room when the switch was thrown and a faulty piece of MC arched inside the cable jacket.

Yeah and more than likely the ground fault was at the cut off point of where the metal cladding was cut and removed for make up. Was the red insulator installed properly. Was the proper tool used for cutting the metal cladding for removal from the conductors.

3/8 in. Flexible Metal Conduit (FMC) Anti-Short

 

I’ve seen a steel staple buried in the sheath of NM cable, (Romex trade Name), and short out the cable. Don’t blame the cable. Blame the guy that drove the steel staple.

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When I ran my MC cable I used metal boxes for the outlets so that the MC cable jacket is attached to the metal outlet box and the metal case of the breaker box.  I believe the metal casing of the breaker box is grounded.  I did not know that the MC cable was twisted but I am glad to know that it is.

Our neighborhood has underground utilities and I share a transformer with one neighbor.  Our house is 23 years old.  I brought home an AQ Niagara 5000 Power Conditioner from my local store (140 miles away) to try out.  I did not take it back. Whatever magic is inside of it, it makes the sound better.  Not sure if it has an Isolation transformer.  The addition of good power cords improved the blackness of the sound as well.

I have a vacuum tube preamp and I hear no noise with my ear to the tweeters.  My phono preamp generates a little tube rush noise that can be heard close to the tweeters; but that is to be expected with 66 dB of gain.  (Moving Coil preamp)

 

PS - Most linear amplifiers use power supplies which are filtered but not regulated. That is, the DC voltage at the power rails is at the mercy of the incoming voltage. A long term change in the incoming VAC will be proportionately reflected in the VDC at the rails.

All the low voltage gear (DAC, preamp, streamer, tuner, etc.) however is always filtered and regulated. A wide difference in the incoming VAC won’t affect the voltage that feeds the circuitry.

Jai, I replace MC because of ground issues.  I experience it in the field.  I really could care less about EMF issues.  You can deal with that in the field.  More EMF issues arise behind your rack than in the wall.  If you know how to run wire.   EMF is teally one of your lesser issues.  

AQ, Shunyata, Isoteck, Torus are all filters with their own technology.  And Voice.  I was pretty pissed when TAS did an article on power conditioners and failed to mention an isolation transformer.  Isolation transformers are in most every recordijg studio around the world for 2 reasons.  One they work.  2, Art kelm who specifies that work finds they work best and uses them.  I like them as I have never heard one do negative things.  Only positive.  And I can feed any amp.  I always am aware what any of the other filters are doing. 

If you hear noise out a speaker, that is ground or equipment issues.  Its not dirty power.  You deal with the issues in different ways.  

If you read Arts site, you will see he calls out metal wire and isolated grounds in his cable runs and associated panels.   There are reasons to like metal.  IMO, its not about geometry or performance.  There are other reasons to like it.   But the positives of metal can easily be overcome in NM when installed correctly with the rught materials.  .  And you don't end up with ground issues.  NM reliably works.   Filters are doing a job that addresses noise on the power line proper wiring or metal encased wire do nothing to address.