[andycsb]

Hello everyone...which material would be better as wall socket mounting boxes? Better as in better damping properties, durability and etc etc. Thanks.

[dBe]

The first thing I would consider would be the dielectric constant of the 2 materials.  Bakelite is ~ 4.8 (air being 1.005-ish) and U/F is typically over 7.   It is easily to mechanically damp boxes so the electrical characteristics drive my choices.

[andycsb]

@dBe. Thanks for your input. Reason why I ask is because I am about to make a purchase of a mounting box. If you had a choice of only one of them as a mounting box...which would you choose? Or would any one of them suffice since it's a close call.

[Speedskater]

What's wrong with steel outlet & junction boxes?
And why would it matter?

[*Scotty*]

I thought the cheap plastic boxes sold at Lowes and Home Depot were made out of PVC, I'm talking about the blue plastic ones. That material could have a dielectric constant of ~ 3 which be considerably better than the two previously mentioned alternatives.
Scotty

[Speedskater]

This is the spec for the most common bulk power wire:

Southwire SIMpull THHN or THWN-2 or MTW copper conductors are soft annealed copper. #14 - 4/0 AWG uses a
combination unilay strand and 250 kcmil and larger uses a compressed copper strand. The wire is insulated with a tough heat
and moisture resistant poly vinyl chloride (PVC), over which a SIM (SLIKQWIK® Infused Membrane) nylon (polyamide) or UL

The wire itself has a PVC insulation so way or how could the box matter?

[dBe]

This is the spec for the most common bulk power wire:

Southwire SIMpull THHN or THWN-2 or MTW copper conductors are soft annealed copper. #14 - 4/0 AWG uses a
combination unilay strand and 250 kcmil and larger uses a compressed copper strand. The wire is insulated with a tough heat
and moisture resistant poly vinyl chloride (PVC), over which a SIM (SLIKQWIK® Infused Membrane) nylon (polyamide) or UL

The wire itself has a PVC insulation so way or how could the box matter?

It doesn't IME.  I use PVC boxes for my stuff.  I didn't even know Bakelight boxes were still available.  I answered his question...

In the tweako end of this obsession steel is avoided due to eddy currents.  That is why high end receptacles are non-magnetic.  In the 5362A P&S the only magnetic parts are the two fixing pins that hold the front and rear moldings together.  #6 brass screws work well there.

Crazy, huh?

[jea48]

This is the spec for the most common bulk power wire:

Southwire SIMpull THHN or THWN-2 or MTW copper conductors are soft annealed copper. #14 - 4/0 AWG uses a
combination unilay strand and 250 kcmil and larger uses a compressed copper strand. The wire is insulated with a tough heat
and moisture resistant poly vinyl chloride (PVC), over which a SIM (SLIKQWIK® Infused Membrane) nylon (polyamide) or UL

The wire itself has a PVC insulation so way or how could the box matter?

The wire itself has a PVC insulation so way or how could the box matter?

Speedskater,

LOL, first thing you will have to do is take off your electrical engineer's hat.
A steel box is made from a ferrous material and therefore has magnetic properties.
Many say ferrous materials used in the power mains branch circuit delivery system can affect the sound of an audio system.

Example if a power receptacle has a steel ferrous supporting back strap.
 Do a search of the archives on Tweakers' Asylum. Lots to read there. And some of the posts are from electrical engineers.

Here is a simple test for you to try. Pull the duplex cover plate/s from the wall outlet/s that feed your audio system and replace them with steel, ferrous, steel plates. Use a magnet to make sure they steel plate is made from a ferrous material. Post back your listening findings, results.

Here are a couple of threads from AA.

http://www.audioasylum.com/audio/tweaks/messages/127995.html

http://db.audioasylum.com/cgi/m.mpl?forum=tweaks&n=79013&highlight=oyaide+outlet+cover+plate&session=
.
Jim

[Speedskater]

Many knowledgeable people don't say anything of the sort.
I do like the topic at audioasylum   'Genuine insanity'
After the AC power goes through 50 to 100 feet of metal conduits & boxes, one more won't make any difference.
I'll let you do the blind test, after all it's your claim.
And I'll stick with good engineering practices, thank you.

[jea48]

Many knowledgeable people don't say anything of the sort.
I do like the topic at audioasylum   'Genuine insanity'
After the AC power goes through 50 to 100 feet of metal conduits & boxes, one more won't make any difference.
I'll let you do the blind test, after all it's your claim.
And I'll stick with good engineering practices, thank you.

Many knowledgeable people don't say anything of the sort.

Why is it then all the audio grade duplex receptacles are made without any ferrous materials in them? Snake oil?

Also I would bet that most Hi-End power outlet distrubution units are made from non-ferrous materials, like aluminum. Snake oil?


After the AC power goes through 50 to 100 feet of metal conduits & boxes, one more won't make any difference.

Ya, that would not make any sense would it.
 How about if the branch circuit wiring was NM cable, (Romex is a trade name of), and the receptacle rough-in box was ferrous steel or plastic? Think that might make a difference?


I'll let you do the blind test, after all it's your claim.

My claim? Where did you read that?  Who said anything about a blind test?


And I'll stick with good engineering practices, thank you.

Curious what did you think of the late Al Sekela post where he ran listening tests using ferrous and non-ferrous cover plates?

Posted by Al Sekela (A) on February 10, 2006 at 09:53:28

I just finished a five-way comparison of outlet cover plates (on 2-gang metal box):
1. no outlet plate (old standard);
2. magnetic SS outlet plate with Nylon screws (verified not grounded with ohmmeter);
3. same, but with one steel screw to ground it;
4. same as 3. with magnets stuck to outside of plate;
5. High-abuse Nylon plate with Nylon screws. Also tested with both 2-gang boxes covered with Nylon plates.

Test CD was Shirley Horn, _You Won't Forget Me_, Verve 847 482-2.

Numbers 1 and 5 were so close I decided to leave the Nylon plates in place.

Number 2 gave an added sense of air and resonance, which led me to test the SS plate for acoustic ringing. It rings like a bell with a pure, sweet, high sustained tone, and a lot of atonal immediate crash like a cymbal. With this thing vibrating near the outlet and not grounded, it is acting like a dynamo and converting acoustic vibration into electrical noise within the power circuit and/or safety earth.

Numbers 3 and 4 dulled the sound compared to number 1: not in the sense of lost treble, but in a lack of midrange presence. With my system tuned up, I can hear Shirley smile as she sings, "...should there be eyes like []yours..." near the beginning of track 12, "You Stepped Out of a Dream." This sense of a smile was diminished with treatments 3 and 4. The piano tone was also less appealing in general. Her voice seemed less cohesive over her range.

Thus, my results are similar to yours with respect to grounded versus floating plates, but I believe the apparent improvement with the ungrounded plate is due to euphonic coloration rather than increased detail retrieval. You can confirm this by listening carefully with the ungrounded plate in place, and then with it removed. Other inmates have observed improved performance with no plate at all on the outlet, but clearly this is not safe for most people and violates code. In my case, anyone who approached the uncovered outlets would probably have died from tripping over the equipment and cables before reaching the outlets, so I was not concerned about the safety aspect. The Nylon plates' appearance matches the other outlets in the room, so I will leave them on.
[/i]

The late Al Sekela was a well respected Electrical Engineer.

[Speedskater]

An interesting paper on AC power wiring.  While Bill Whitlock has been hinting at this for decades, this paper enplanes it in detail. Just skip over the math parts and don't even try to read the patent application.

Ground Loops: The Rest of the Story
Bill Whitlock, AES Fellow and Jamie Fox, P.E.

This paper was presented at the AES 129th Convention, 4-7 November 2010, San Francisco, CA, USA

ABSTRACT

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.

http://xa.yimg.com/kq/groups/20963848/268252969/name/Whitlock-Fox+-+Ground+Loops+.pdf

[jea48]

An interesting paper on AC power wiring.  While Bill Whitlock has been hinting at this for decades, this paper enplanes it in detail. Just skip over the math parts and don't even try to read the patent application.

Ground Loops: The Rest of the Story
Bill Whitlock, AES Fellow and Jamie Fox, P.E.

This paper was presented at the AES 129th Convention, 4-7 November 2010, San Francisco, CA, USA

ABSTRACT

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.

http://xa.yimg.com/kq/groups/20963848/268252969/name/Whitlock-Fox+-+Ground+Loops+.pdf

Note Figure 7, of page 7 of 9. I noticed aluminum armor MC Cable was used for the test. I wish Bill would have ran the same test using steel armor MC Cable as well.

http://www.afcweb.com/product-category/mc-metal-clad-cables/

[Speedskater]

A Middle Atlantic white paper. Remember to read the Addendum.

"Power Distribution and Grounding of Audio, Video and Telecommunications Equipment White Paper"

"Addendum to Power Distribution White Paper"

http://www.middleatlantic.com/resources/white-papers.aspx

[jea48]

A Middle Atlantic white paper. Remember to read the Addendum.

"Power Distribution and Grounding of Audio, Video and Telecommunications Equipment White Paper"

"Addendum to Power Distribution White Paper"

http://www.middleatlantic.com/resources/white-papers.aspx

Thanks for the link.

Middle Atlantic is referring to AC cable and not MC cable. And the AC cable they are talking about has an insulated grounding conductor for use of an IG,  isolated grounding, type receptacle as well as a bare equipment grounding conductor for the outlet box ground. I personally do not care for AC cable.

>>>>>>>>>> 


http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

Page 35 clearly shows an MC Cable with three insulated conductors on the plot for the MC Cable. An insulated equipment grounding conductor and two current carrying conductors.  For a 120V branch circuit , a black Hot conductor, white neutral conductor, and green equipment grounding conductor. In every 3 conductor MC Cable I have seen the 3 insulated conductors are tightly twisted together in a spiral configuration then covered with a tightly wrapped plastic wrapping, then incased in the armor cable. Because of the construction of the cable it is impossible for the wires to more from their manufactured lay within the cable. The wires are like sardines in a can so to speak.
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

The Middle Atlantic Link you provided did get me thinking about MC Cable that has two insulated equipment grounding conductors. There in, one for the box ground and the other for an IG grounding type receptacle. I could see in this instance even though the conductors are tightly grouped and twisted in a spiral configuration the lay of the two ground wires would not be the same as the 3 wire MC cable and would not necessarily cancel the so called transformer effect of a voltage being induced on the two equipment grounding conductors possibly causing a ground loop hum or buzz.

At any rate this still does not address the question if the wires are in a steel armor cable will the ferrous steel have an effect on the sound of an audio system?
Jim

[Speedskater]

a] Because both the Send and Return currents are going through the same conduit the fields will cancel out.
b] These currents then go through a ferrous steel power transformer.  But in this case, the Send enters one end of the transformer while the Return exits the other.  So the fields don't cancel, yet the transformer works as it should.  And small high-frequency signal transformers also work correctly.

[Speedskater]

Here is another paper that has a section on AC cables and conduits. See page25.  More recent thinking, focus's less on power line separation and more on reducing the loop area. This means routing the audio system AC power and signal cables along the same path.  One wire expert suggests taping the AC power and signal cables together.

"Power and Grounding for Audio and Video Systems"
'A White Paper for the Real World – International Version'

Jim Brown - Audio Systems Group, Inc.

Considerable confusion seems to surround power and grounding for audio and audio/
video systems. This “White Paper” is an attempt to cut through the confusion and
set out a collection of good engineering practice that is both safe and effective while not
requiring specialized or costly measures to avoid hum, buzz, noise, or RF interference.
The author believes that the recommendations and practices outlined herein are safe,
and that they conform to building codes in most of the world. The author is an electrical
engineer by training and an audio systems consultant by profession,

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

[jea48]

The “Conduit Transformer”

• This finally explains what drives 99% of all ground loops!
• Load current in line and neutral produces opposing magnetic fields
since instantaneous current flow is in opposite directions
• 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®
• Voltage is directly proportional to load current, wire length, and
rate of change in current or ΔI/Δt
• Mechanism favors high-frequency harmonics of 60 Hz
• For constant current in L and N, induced voltage rises at 6 dB/octave

Bill Whitlock, 9/4/2012 Overview of Audio System Grounding & Interfacing
[/i]

I think Bill Whitlock should not have titled what happens, depending on where an equipment grounding conductor is physically placed within close proximity of two current carrying conductors of a circuit, The “Conduit Transformer”.  The magnetic field of a current carrying wire can induce a voltage onto a wire within its magnetic field space.

I would bet if the same test was run using, say, #12-3 with ground NM cable where the black wire is the hot, white the neutral, red wire taped green in color and used as an insulated isolated grounding conductor, and the bare wire as a box ground, the test results would be poor. The reason being, the placement of the red insulated wire in the NM cable construction with respect to the hot and neutral current carrying conductors. I would bet an AC voltage would be induced onto the insulated isolated equipment ground wire.

From Bill Whitlock's White paper it appears the ideal 120V with ground circuit consists of only three conductors closely positioned with the equipment grounding conductor placed between the hot and neutral current carrying conductors. Or better yet the hot and neutral conductors twisted together with the ground wire ran along side the twisted pair be it in steel conduit, aluminum conduit, and PVC conduit, or in free air.

[Speedskater]

Why would you use an Isolated Ground with a Romex®NM cable?

[jea48]

Why would you use an Isolated Ground with a Romex®NM cable?

I wouldn't.