Dedicated Audio Power Circuit

[Speedskater]

Len,
You can use BX wiring in a 10 gauge. [............]

"BX" cable??? Is that a typo or a mis-identification? "BX" is a very old cable type (pre WWII).

From the Middle Atlantic paper:

Armor Clad – Designated (AC) by the NEC, and sometimes called “BX”, its original manufacturer?s trade name. While it is the least expensive, is the least desirable for AV systems due to the fact that there is no supplemental grounding conductor (wire). The metal jacket, along with its aluminum bonding strip, is the safety grounding conductor and is detrimental to AV performance due to its higher comparative impedance than a solid piece of copper wire. Without a supplemental grounding conductor, the ground impedance and integrity is dependent on the length of the sheath and all the connectors and fittings (in series). BX cannot be used with isolated ground receptacles.

 

[Speedskater]

Why? I would have expected twisted pairs to have higher capacitance and thus better HF attenuation.

In the real world, unless you are in a very high EMI environment, I would not expect any significant difference between Romex and twisted pairs, though I find the stranded twisted pairs easier to handle than Romex.

For AC power, a twisted pair plus Safety Ground would be great. But installing the conduit for it will not be easier than running Romex®.

 

[CGabriel]

"BX" cable??? Is that a typo or a mis-identification? "BX" is a very old cable type (pre WWII).

From the Middle Atlantic paper:

Armor Clad – Designated (AC) by the NEC, and sometimes called “BX”, its original manufacturer?s trade name. While it is the least expensive, is the least desirable for AV systems due to the fact that there is no supplemental grounding conductor (wire). The metal jacket, along with its aluminum bonding strip, is the safety grounding conductor and is detrimental to AV performance due to its higher comparative impedance than a solid piece of copper wire. Without a supplemental grounding conductor, the ground impedance and integrity is dependent on the length of the sheath and all the connectors and fittings (in series). BX cannot be used with isolated ground receptacles.

http://healthybuildingscience.com/2013/01/15/residential-wiring-best/

Apparently the term BX is being phased out with the new term being MC.

http://electricalwire.biz/MC_Cable/Type_MC_Cable_Copper_Electrical.html

An isolated ground outlet is irrevevant unless you run rigid conduit and use a metal electrical box. The "isolation" term refers to the ability to remove conductivity between an outlet's ground strap and the metal box and the associated metal conduit. It is primarirly used in commercial buildings when RFI/EMI that may be present on the conduit from being transmitted to the ground strap of the outlet. An isolated ground outlet does nothing when installed in a plastic electrical box and or if metal conduit is not used.

 

[Speedskater]

An "Isolated Ground Circuit" could be important any time you use metal conduit either flexible or rigid! Or have metal outlet boxes attached to metal wall framing or touching other metal objects like HVAC ducts or metal pipes.

Note that many electricians don't understand that the reason we want an "Isolated Ground Circuit" is to prevent ground currents, lost neutral currents, noise & leakage currents from other circuits (and maybe other building) from using our interconnect cables as a path to return to their source. 2nd note: The source that all the above currents are trying to return to is that big power company transformer outside. They have no interest in going into the dirt.

Also note that many audiophiles don't understand that "Isolated Ground Circuit's" are only useful when the conditions in the first 2 sentences exist.

 

[CGabriel]

Very true.

 

[DonH50]

For AC power, a twisted pair plus Safety Ground would be great. But installing the conduit for it will not be easier than running Romex®.

True, but our local code does not require conduit for the round power cables in the house that have hot/neutral/ground twisted in one sheath. That's what they used when they finished our basement, and the usual staples but rounded instead of flat as for Romex.

Off-topic: How did you get the registered trademark symbol?

 

[Speedskater]

I'm not familiar a round in-wall AC power cable.

® registered trademark symbol = [Alt]0174 =®

 

[brad225]

Is it possible that the round cable was a 3 wire plus ground (2 line, 1 neutral and ground) for multiple circuits? That is generally round though I have never seen different wire staples used with it.

 

[Roysen]

I wonder how long before somebody uses shielded silver inside conduit from their service to the outlets...

I actually do. We have 230V service here and I have seven dedicated 16A circuits, one for each planned source, preamp and phono stage. They are all wired with a Oyaide in-wall silver cable at 8 square millimeters from the breaker box to the Furutech outlet. Then I have two 32A dedicated circuits for power amps. They use a copper 16 square millimeter cable from breaker box to Phillip Hauge industrial outlets (similar series used by among others Boulder on their amps power inlet).

Each cable from breaker box to outlet are kept short (3 meters) and exatcly equally long ro avoid ground loops.

The breaker panel is dedicated to the hifi system and connected to a three phase 80A 230V circuit in the house main breaker panel. A three phase copper cable of 16 square millimeter is used from the house main breaker panel to the hifi breaker panel.

 

[microstrip]

I am much more less ambitious. I have three separate dedicated 230V AC runs from the house breaker box, using 6 mm2 copper cable, and I am firm believer in the "2m rule" - the last 2m of power cable make 99% of the difference!

 

[LL21]

I actually do. We have 230V service here and I have seven dedicated 16A circuits, one for each planned source, preamp and phono stage. They are all wired with a Oyaide in-wall silver cable at 8 square millimeters from the breaker box to the Furutech outlet. Then I have two 32A dedicated circuits for power amps. They use a copper 16 square millimeter cable from breaker box to Phillip Hauge industrial outlets (similar series used by among others Boulder on their amps power inlet).

Each cable from breaker box to outlet are kept short (3 meters) and exatcly equally long ro avoid ground loops.

The breaker panel is dedicated to the hifi system and connected to a three phase 80A 230V circuit in the house main breaker panel. A three phase copper cable of 16 square millimeter is used from the house main breaker panel to the hifi breaker panel.

That's just cool...

 

[scooter]

I am having ground loop issues and this thread seemed like a good place to ask. I installed a sub-panel to feed my audio system. I have installed 4 20A circuits with 10GA stranded wire. Each circuit is an isolated ground with a PS Audio Power port. All electrical is home run from the panel to the outlet with no splices. To meet code, the metal conduit raceway has its own ground but that ground runs to the main panel (in theory, never touches the audio). The outlets are all on the same leg in the panel. The breakers are standard breakers (not arc fault or ground fault). Long story short, I get a nasty buzz when just the amps and preamp are connected via an unbalanced interconnect. I don't know how to get rid of it and thought that I had the electrician do everything right. What could have gotten screwed up?

 

[DonH50]

Since the power ground goes back to the service, if I understand your runs, and the signal cables are local among components, that seems like a classic ground loop and I am not sure I see a way out. I am unfamiliar with the PS Audio Power but would be very surprised if it isolated the safety ground -- that would violate code around here.

Safest solutions are to go balanced if possible, add ground isolators on the signal cables (transformers or DI boxes), add chassis ground wires among the components to a single ("star") safety ground point to one of the circuits, or put amps and preamps on same line. You could float the safety ground but that would violate code and potentially be a safety hazard.

 

[CGabriel]

I am having ground loop issues and this thread seemed like a good place to ask. I installed a sub-panel to feed my audio system. I have installed 4 20A circuits with 10GA stranded wire. Each circuit is an isolated ground with a PS Audio Power port. All electrical is home run from the panel to the outlet with no splices. To meet code, the metal conduit raceway has its own ground but that ground runs to the main panel (in theory, never touches the audio). The outlets are all on the same leg in the panel. The breakers are standard breakers (not arc fault or ground fault). Long story short, I get a nasty buzz when just the amps and preamp are connected via an unbalanced interconnect. I don't know how to get rid of it and thought that I had the electrician do everything right. What could have gotten screwed up?

Sorry to hear that you have a ground loop issue. This is actually quite common when installing multiple dedicated lines. Unfortunately, it is not always easy to solve the problem. First, we need to determine if the lines that you installed are the cause.

1) Did you hook ALL the audio equipment to just one of the dedicated lines? Do you have the buzz when everything is connected to the same line?

2) Do you have any video components connected to this system?

3) Is the amp or preamp a tube type?

Questions for the electrician:
A) Are the ground and neutral bonded together in the sub-panel? (This is the number one error made when installing sub-panels)

B) Are the ground wires in the conduits insulated or bare copper?

C) Are the measured lengths of the dedicated line runs all the same? When you have more than one dedicated line in a system you must ensure that the impedance of the lines are all equal. This can only be accomplished if the lines are equal in length and the wires are all the same type and gauge.

D) Are there any junction boxes used for any of the dedicated line runs?

 

[CGabriel]

Yes, Don has a very good point. Is the PS Audio outlet an isolated ground type?

 

[scooter]

Sorry to hear that you have a ground loop issue. This is actually quite common when installing multiple dedicated lines. Unfortunately, it is not always easy to solve the problem. First, we need to determine if the lines that you installed are the cause.

1) Did you hook ALL the audio equipment to just one of the dedicated lines? Do you have the buzz when everything is connected to the same line?

2) Do you have any video components connected to this system?

3) Is the amp or preamp a tube type?

Questions for the electrician:
A) Are the ground and neutral bonded together in the sub-panel? (This is the number one error made when installing sub-panels)

B) Are the ground wires in the conduits insulated or bare copper?

C) Are the measured lengths of the dedicated line runs all the same? When you have more than one dedicated line in a system you must ensure that the impedance of the lines are all equal. This can only be accomplished if the lines are equal in length and the wires are all the same type and gauge.

D) Are there any junction boxes used for any of the dedicated line runs?

1) Buzz goes away when I hook it all up to the same outlet

2) Yes but I disconnected it all as a test. Still there when disconnected (including the catv coax). With just preamp and amp connected, still buzzing.

3)preamp is SS. I have both tube and SS amps (bi-amped) Maggie's.

A) Need to ask. Should they be bonded together?

B) Insulated 10 Gauge stranded

C) This got screwed up. The two in front are the same. The two in rear are the same. But the front and rear are different. I connected the amp using an extension cord to the rear and still buzzed.

D) Each outlet sits in its own metal box. The inside of the house for the audio outlets is all connected with metal conduit. The conduit all comes together in a central junction box. Here is where it gets ugly. We had to bury the long run from the junction box to the panel in the ground 18" down in PVC. The house is built on slab and tearing apart the house was not an option. The metal raceway is bonded separately to its own ground. There are no splices in any of the wires.

 

[scooter]

Yes, Don has a very good point. Is the PS Audio outlet an isolated ground type?

Yes. They have the orange triangle on them and the instructions indicate its an isolated ground outlet.

 

[CGabriel]

1) Buzz goes away when I hook it all up to the same outlet

2) Yes but I disconnected it all as a test. Still there when disconnected (including the catv coax). With just preamp and amp connected, still buzzing.

3)preamp is SS. I have both tube and SS amps (bi-amped) Maggie's.

A) Need to ask. Should they be bonded together?

B) Insulated 10 Gauge stranded

C) This got screwed up. The two in front are the same. The two in rear are the same. But the front and rear are different. I connected the amp using an extension cord to the rear and still buzzed.

D) Each outlet sits in its own metal box. The inside of the house for the audio outlets is all connected with metal conduit. The conduit all comes together in a central junction box. Here is where it gets ugly. We had to bury the long run from the junction box to the panel in the ground 18" down in PVC. The house is built on slab and tearing apart the house was not an option. The metal raceway is bonded separately to its own ground. There are no splices in any of the wires.

The answer to #1 confirms that you have a power circuit related ground loop.

Without knowing the answers to A and B below there is no sense in suggesting any solutions.

REF #A: Electrical panels come with the ground buss and neutral buss bonded. The electrician needs to break the bond when used as a sub-panel. The neutral grounds should only be connected to a safety ground or buss at the main panel.

REF #B: Be sure that the ground wire in each outlet box is NOT touching or connected to the metal box. If it is this establishes different paths to ground and potential differences.

REF #D: This could be a problem. The sub-panel chassis and its metal conduit lines have no continuity to the main electrical panel since it was run through PVC. You say that the sub-panel has its "own" ground. What exactly does that mean? Where does the ground wire go? It should be connected to the ground wire that comes from the main electrical panel not connected to another ground rod or to a metal water pipe for instance.

Assuming A and B are good:

REF #3: Run just the SS amp and then run the Tube amp. See if it is just the tube amp that buzzes.

Remember that ground loops can occur when there is a potential (voltage) difference between the grounds of the different dedicated lines. When installing dedicated lines, a major objective should be to minimize any impedance difference between neutral and ground lines. This is why you want the same type and gauge of wire and that they be nearly the same length. You can get very similar problems of impedance differences between dedicated lines by inserting different power distributors ( power strip or power conditioner) or different types of power cables from the power distributor to the wall. This includes inserting extension cable(s) on one or more of the lines. They are almost universally high in impedance compared to in-wall wiring.

Try connecting the entire system to the two front circuits that are equivalent in length. Use the same or similar power strips and power cabling. If you use a extension cord to connect the amps be sure to use the same type and length extension cord on the other circuit to make them equivalent. See if you get the buzz. This will tell you if you just have a problem with the rear circuits.

Good luck,

 

[Speedskater]

The Isolated Ground wires should join together in the same sub-panel box as the Hots and the Neutrals. But they should connect to an IG bus not the main Safety Ground bus. The total length of the Hot, Neutral and IG wires leaving the sub-panel box to the outlets should all be the same.

Hopefully you planned the location of the sub-panel in a central location so that most of the wire length was from the main-panel to the sub-panel. Thus reducing the wire length from outlet box to outlet box

Also that all of your audio power circuits are on the same 120V leg (aka phase).

 

[Speedskater]

After further thought, it's probably a power wiring error. Back when Audio Precision built their new building they found many, many errors. It's either a Bootleg Ground or the Isolated Ground and the Safety Ground are cross-connected.

Mike Sokol, who moderates a pro audio sub-forum on AC power, also has a article on bootleg grounds.

[h=1]Failures in Outlet Testing Exposed[/h] Jul 15, 2013 Mike Sokol | Electrical Construction and Maintenance

Why standard outlet testing methods fail to reveal reverse polarity bootleg ground miswiring situations

http://ecmweb.com/contractor/failures-outlet-testing-exposed