Dedicated power circuits

@8th-note,

.

 

~ ~

Is this what you are looking to buy? You do know it is 120/240V? Best practices is to feed audio equipment, (that is connected together by wire ICs), is to feed the 120V equipment from branch circuit breakers fed from same Line. All from Line 1 or all from Line 2. Not from both.

 

You mentioned Michael Fremer’s new electrical service. All his audio equipment is fed from one 120V Line. I have no idea how big his total load is though. Just a guess a lot more than yours.

.

 

 

 

~ ~

I watched the video again today and picked up a few things I missed the first two previous times. I believe there are a few things worth noting.

Near the end of the video Fremer shows the new sub panel for his audio room. It is fed 120V only. *(1)* Electrical Inspector did make the electrician install the other 120V hot conductor. It will not be used though. I think it was just an AHJ Inspector thing. I couldn’t find anything in the NEC that requires it.)

Note the 120V feeder for the sub panel is installed in PVC conduit. All the branch circuit wiring is installed in non metallic flexible conduit.

Example, non metallic flexible conduit:

1/2-in x 25-ft Ultratite Non-metallic Schedule 80 Liquid-tight Conduit

From what I could see the outlet boxes are also non ferrous as well as the outlet cover plates. I did see something I didn’t agree with though. Two dedicated circuits for the two mono amps were pulled in the same raceway, conduit. That doesn’t follow best practices. I did notice though the 120V Hot, Neutral, and Ground branch circuit wiring used for each 120V circuit was apparently tightly twisted together. That would be a whole lot better than if single conductors for both dedicated circuits were all pulled loosely together in the conduit. That definitely is a no, no. A sure way to induce an AC voltage onto the equipment grounding conductors and cause ground loop hum.

Image of audio room sub panel, front cover removed. Note the two 120V dedicated circuits bottom right side of panel in the flex conduit connector.

.

 

.

/ / / /

 

Not to bad mouth the electrician. He may have had his reasons... I did notice a few things on the installation of the new electrical service I didn’t care for.

The use of a rigid no-thread coupling on the Mast rigid Conduit. (Yeah it meets code. But...)

The use of the offset nipple into the top of the meter socket enclosure hub. Not pretty...

And I found myself scratching my head why the electrician used PVC conduit nipple from the bottom of the meter socket enclosure to the Myers Hub on the main service equipment panel. A galvanized rigid nipple would have looked a lot better, jmho... As well as electrically bonding the two metal enclosures together.

 

/ / /

 

*(1)* Electrical Inspector did make the electrician install the other 120V hot conductor.

I have a friend in Texas that has a 15KVA 240V to 120V single phase pad mount outdoors isolation transformer strictly for feeding his two channel audio room equipment. The electrician only installed one, Hot, neutral, and ground, conductor to feed the 120V only electrical panel. The electrical inspector made the electrician add the additional spare conductor for the other hot Line, ( for future), not used, not connected.

.

I had to have the second phase run at Fremers because I could not get a letter from SqD saying a Square D subpanrl rated 120/240 was suitable for 120 only.

That jogged my memory. Sounds like the Electrical Inspector was using NEC 110.3 (B). Square D manufactured the Load Center to be connected to a split phase 120/240V AC source. The ampacity rating of the neutral bar can be, is, sized smaller for a split phase AC source because as you know the service neutral only carries the unbalanced load back to the neutral of the secondary winding of the power transformer. The neutral bar ampacity rating would not be rated big enough if the panel was connected to a 120V only source. (IF the panel was loaded to its full rated capacity.) There is the problem.

After reading your post I remembered having a conversation with my friend in Texas when I suggested feeding the electrical panel for his audio room equipment 120V only. In my friend’s case the panel was fed from a 15KVA isolation transformer. (Primary 240V, secondary configured for 120V only). I remembered talking to him about the electrical panel and the possible problem with the electrical inspector approving it connected to 120V only. I told him the ampacity rating of the neutral bar would be the possible problem. It depends on how well the inspector is versed on the NEC... He said, can’t I have my electrician just change out the neutral bar? No... Doing so will void the UL Listing. The Electrical Inspector, if his knows the NEC, as well as the electrical panel, will spot the neutral bar was changed out and flag the panel, If the panel was modified it needed to be re-Listed for the modification. No Listing, it can’t be installed. (NEC 110.3 (B) (C) ).

As for the panel for the audio room my friend wanted the best. Money was no object... Imo, a Square D panelboard with QOB bolt on breakers.

His isolation transformer would be 15KVA. At 120V the xfmr was good for 125A. I suggested he over size the ampacity rating of the panel. I can’t remember what I recommended. I do remember the Electrical Inspector passed it being fed 120V only but required the Electrician pull/install a spare conductor the same size as the existing ungrounded conductor for future, possibility of, feeding the panel 120/240V.

/ / / /

As for Fremer’s video, he made the day of rewiring of the electrical service for his home, I cringed every time Fremer would say "every thing according to code". He said it several times in the video. I was surprised you guys didn’t suggest he stop saying that... As you know Code is bare minimum electrical safety standards... NEC could care less how an audio system sounds. All NEC cares is if it is electrically safe...

Jim

 

I don’t like MC cable or wire in a steel pipe.

I agree with your statement for use of steel armored MC cable or loosely pulled conductors in a steel conduit for the reasons you stated in your post dated 02-24-2023.

I do like and recommend 2 wire with ground solid core copper conductor aluminum armored MC cable though. ( MC, not, AC cable. ) The aluminum armor does reject some RF from entering the cable. What I like about aluminum armored MC cable is the Hot, Neutral, and insulated EGC, conductors are twisted in a spiral twist and held firmly, tightly, together by the aluminum armor.

Price for solid core copper 2 wire with ground aluminum armor MC cable is competitive with NM cable in my area. I agree twisting the hot and neutral current carrying conductors together and pulling the EGG along side the twisted pair pulled in conduit is better than AL armored MC but the difference, to me anyway, does not justify the additional cost, especially the labor cost... If cost is no object well then....

Note: MC cable should only be installed by a licensed electrician that has experience removing the armor from the wire for termination.

Jim

/ / / /

For anyone interested:

Power Distribution and Grounding of Audio, Video and ...

Read pages 4 and 8.

Closely read pages 11, 12, and 13.

For Isolation transformers read page 19.

.

Make sure you tell the electrician you want 10/2 with ground SOLID copper conductor aluminum armored MC cable.

"MC", NOT "AC" armored cabled. Make sure he repeats to you it will be MC cable.

 

Be careful what you are buying now days when it comes to Hubbell outlets. Hubbell today it not the company it was years ago. Different owner.

What are looking at buying? How many outlets are you looking at buying?

So where do I find this twisted mc cable? All i see is untwisted or straight.

It's not straight, trust me.

Example of what to buy:

I highly recommend you hire an electrician to install MC cable.

.

.

 

 

 

 

 

Think of all the issue you are creating. 

Like what?

 

Are you sure, maybe, you didn't remove AC AL armored cable?

How many wires are in 10/2 and what are they.

@kingrex

I assume you mean in MC.

3 insulated conductors. 2 Line conductors, 1 green insulated EGC.

You should know that🤔...

kingrex

74 posts

02-26-2023 at 02:13pm

Southwire Armorlite 125-ft 10/2 Solid Aluminum MC Cable

You sure you want to recommend this cable. Think of all the issue you are creating. I would never use it. Its what I removed from Fremers that was causing lots of issues.

And I’m pretty sure its not twisted anymore. Most all that stuff is strait transmission line. Its held together so the impedance/capacitance is stable.

If your really concerned about rejecting noise, put an isolation transformer in for amps. Size it to feed the whole system. Or use an Audio Quest type filter on the front end and amps to the wall. Either of those solutions will get rid of a lot of noise. MC does not get rid of any noise. The aluminum may block a small amount of RF on the branch only. Aluminum does not do much for EMF when cables are places side by side.

I personally say stick with Southwire NM cable or spend more and get grain oriented twisted.

.

You sure you want to recommend this cable. Think of all the issue you are creating. I would never use it. Its what I removed from Fremers that was causing lots of issues.

Just a guess you removed AC cable from Fremer’s house. Not MC cable. Heck I don’t think you have ever worked with MC cable the way it sounds.

This statement of yours kind of says it all.

How many wires are in 10/2 and what are they.

To be more precise there is a black, a white, and a green EGC. All three conductors are the same AWG size. The Insulation covering the wire is THHN.

Here’s a picture of 2 wire MC cable for you to look at.

Southwire 8 ft., 12/2 Solid CU MC (Metal Clad) Armorlite ...

.

Here’s a picture of AC cable for you to look at.

12/2 x 250 ft. Solid CU BX/AC (AL Armored Cable) ...

A 16 AWG bare aluminum bond wire to be used in conjunction with the armor for the EGC. AC is junk, imo.

 

And I’m pretty sure its not twisted anymore. Most all that stuff is strait transmission line.

It was manufactured in a spiral twist yesterday, and it will be manufactured in a spiral twist tomorrow, and the next day and the next day, and the next day after that. Like I said, I don’t think you have ever worked with MC cable.

 

If your really concerned about rejecting noise, put an isolation transformer in for amps. Size it to feed the whole system. Or use an Audio Quest type filter on the front end and amps to the wall.

Wheres that coming from? Read the OP’s original message.

 

I personally say stick with Southwire NM cable or spend more and get grain oriented twisted.

You can have your opinion. I have mine. Of course there has been testing comparing NM sheathed cable to MC armored cable.

NM works fine providing the installer of the cable takes extra care not to twist the cable while installing it so as not to distort the lay, placement, of the bare EGC between the two current carrying conductors.

With MC cable that can’t happen. The Hot, neutral, and insulated ground spiral twist is held tightly together it’s entire length by a plastic wrap and the metal armor. Be it aluminum or steel.

The testing I talked about. I have two white papers for you to read.

An Overview of Audio System Grounding and Interfacing

.

Take a look at page 16.

Read pages 31 thru 36. Pay close attention to page 35.

Page 35 chart.

Al armored MC cable beat out NM cable. I wonder how careful the techs were with the NM. I bet they didn’t twist it, changing that exact lay, position, of the bare ground wire between the two current carrying conductors.

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

Of course you can’t always count on it.

.

Power Distribution and Grounding of Audio, Video and ...

Read pages 11, 12, and 13.

Pay close attention to the chart on page 13. Again Al armored MC beat out NM cable.

Oh and look at the picture of the test board. The NM is laying flat. No twists. Wish they would have tested it with at least a couple light twist in it. Just like in the real world.

Good luck pulling NM cable without getting any twists in it.

You still want to recommend NM cable over AL armored MC cable?

.

or spend more and get grain oriented twisted.

There’s a sales pitch to buy your 2 conductor with insulated ground THHN, maybe, THHN/THWN twisted cable assembly.

.

Best regards,

Jim

.

Old White Paper. Middle Atlantic Products, Inc.

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

( Rev 2b 8/7/2007 )

.

Newer white Paper. Middle Atlantic Products, Inc.

Integrating Electronic Equipment and Power into Rack ...

( Rev 4b 2002-2010 )

.

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).

.

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...

.

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?

.

/ / / /

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.

.

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...

.

/ / / /

.

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.

.

 

 

Kingrex said:

 

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.

 

You are the first person that has raised ground issues with MC cable, at least on the audio forums I follow.

Could you expand on the problems you have experienced? If it is ground loops, it’s not the MC cable itself causing the ground problems. From what I have read is the audiophile that had MC cable installed are happy with the MC dedicated branch circuit(s).

.

 

I really could care less about EMF issues..

Where did that come from??? Not from my above post. 🤔

 

The subject matter of my post is about induced voltage by the magnetic fields generated by the Hot and Neutral current carrying conductors onto the EGC of the branch circuit wiring.

Therein, NM cable vs MC cable. If you read the two Links I provided it is proven, by measurements, MC cable does a better job of preventing the magnetic fields generated by the current carrying Hot and Neutral conductors from inducing a voltage onto the EGC.

 

FYI, The bigger the connected load on the branch circuit conductors the bigger, the greater strength, of the magnetic fields. So it would stand to reason a big hungry power amp connected to one dedicated circuit would draw more current than say a CDP on another dedicated circuit.

The EGC of the branch circuit with the power amp would be more susceptible to the chance of an induced voltage onto the EGC of an NM cable branch circuit that an MC cable branch circuit. (Especially long branch circuit runs). Therein with MC cable there would be less of chance of a difference of potential between the two EGCs of the two branch circuits than NM cable. YMMV...

 

The worst branch circuit wiring method would be to loosely pull conductors in a conduit. Worst yet is more than one dedicated circuit with conductors loosely pulled in the same conduit. Sure fired way to create ground loop hum problems.

.

Kingrex said;

Interesting question. A little while back I had a project where I had to run 55 feet, 2 circuits in one pipe on the outside of a house. I spun the hot and neutral only on the 2 circuits and pulled the grounds loose in the pipe. I measured 0 mv between any of the neutral to grounds. I was quite surprised at this as I usually see maybe 5mv to 20mv. It has made me want to set up a test in my own system and measure whether it is best to leave the ground loose or twisted.

.

I spun the hot and neutral only on the 2 circuits and pulled the grounds loose in the pipe.

I’ve posted that on this forum in the past. I first read about it, here:

An Overview of Audio System Grounding and Interfacing

Look at the chart/picture on page 35. Note, Twisted L-N beat out all the others. The EGC is pulled in the conduit along side the twisted pair.

A little while back I had a project where I had to run 55 feet, 2 circuits in one pipe on the outside of a house.

Best practices dictates a true dedicated branch circuit used for sensitive equipment does not share a conduit or cable assembly with other branch circuits.

I spun the hot and neutral only on the 2 circuits and pulled the grounds loose in the pipe.

NEC only requires one EGC sized for the largest circuit breaker handle amp rating of the circuits that share the same conduit.