Isolation Transformer and Subpanel recommendations


There are many isolation transformers out there new and used. What are the best recommended 5kVA/other isolation transformers for high-end audio setups. I live in the US so I need one that would be configurable for 110/120V output. I intend to put this on my dedicated circuit after my main panel in the house. The dedicated circuit is high-quality and 20-amp/10-guage in nature; this circuit is 110/120V, not 220. I'm looking for any recommendations for units that run quiet and have high common-mode noise rejection.

Also looking for recommendations on good quality sub-panels.

Thank you in advance for the assistance!
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Plitron transformers perhaps or even the Torus site.
Thank you very much for the response!
I sent you a message via the new audiogon messaging system. Hopefully it works.
Quick search on Ebay turned up empty for this size and 120V. Generally prefer iron core instead of wide-band toroidal for this purpose. If it's going to be close to the rest of the system, toroidal has the benefits of less stray EM and more convenient packaging. Without step-down....

http://www.surplussales.com/transformers/IsolationXmers-3.html

Although, if you can get 240V there, options get much wider and less expensive. Perhaps even the option of center-tapping, if derated by half.
Thank you for the help and pointer; we can get 240V here up to the house but given it's US, it has to be broken into 2 120V phases inside the house. I'll check out the link you sent.....thanks!
we can get 240V here up to the house but given it's US, it has to be broken into 2 120V phases inside the house.
"it has to be broken into 2 120V phases inside the house."

Would you care to expand?
Noise is unpredictable for either type, aggrevated by external conditions. Potential advantage of tighter windings of toroidal is offset by greater sensitivity to same conditions. Some people mount the transformer near the electrical panel (basement?), away from the living space.

Dryers and ovens are usually 240V.
Jea48: the wiring in our houses here is 120V and 240 comes into the house and is split out normally. I did have an error in my response in that we are not obligated to only have 120V here. I currently have a 240V line to the kitchen where an old electric stove used to be, another for a heat pump, and a 3rd for the dryer to the laundry room. I could choose to run a 240V line to the attic for an isolation transformer if I had to. For that matter, I could also choose to drop an entire 2nd house circuit immediately after the meter and skip the main breaker panel altogether; my response was more thinking of limiting the invasive electric/structure work that would be required here. My apologies for the confusion my original response probably caused...
Zephyr24069,

I would feed the 5 Kva xfmr with 240V balance power.

If your plan was to install the xfrm by your audio equipment so you could use the existing dedicated circuit you now have, you can still use a 240V fed xfmr.

The existing dedicated branch can easily be converted to 240V. The #10 wire is rated for 600V.
Jea48: Thank for the help and advice; my plan is to install the transformer in an adjoining attic over a garage where any humming from the transformer will not be hear and any heat will dissipate. The attic does get hotter in the summers (have thermostat-controlled fans on either side of attic) but overall I think is the best option as I can also have a platform built to bolt the transformer to in the attic as well as investigating any vibration damping solution I might need to ensure the results are optimal.
my plan is to install the transformer in an adjoining attic over a garage where any humming from the transformer will not be hear and any heat will dissipate.

Not a good idea..... I doubt you will find a licensed electrician that will do it.

Why not mount the xfmr on a wall in the garage. It can be mounted up high near the ceiling. (At least 12" down from the ceiling for heat dissipation)

Is the main electrical panel for the house in the garage?

Where are you planing on mounting the new electrical panel that will be fed from the xfmr?
The main electrical panel is in the laundry room, on an inside wall but adjoining the garage....I was either planning on mounting the new subpanel there or in the attack adjoining the room that has my system.
For 240V, as an example...

http://www.ebay.ca/itm/FPE-5-KVA-1-Phase-240X480V-120-240-Volt-3R-SE2N5FS-Transformer-NEW-/310425276037?pt=BI_Circuit_Breakers_Transformers&hash=item4846c9ce85

Sola/ Hevi-Duty and Acme are usually the best bets for sheilded like this one. (the dashed line in the schematic)
So the transformer could be mounted in the garage and fed from the main panel relatively easily.

From the new transformer the load feeder could pass through the ceiling across the attic and drop down through the top plate into the wall cavity to the new recessed electrical panel. (Assuming the wall is studs covered with drywall.)

For resale you might want to install the new panel in the laundry room. Your electrician will show you your options to meet NEC code for minimum working clearances.

Example, the electrical panel cannot be mounted above the washer or dryer.

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In case you didn't know.

A 5 Kva xfmr primary FLA @ 240V is 20.8 amps when fully loaded. Per NEC FLA is used for determining wire size to feed the xfmr as well as the breaker.
Min wire size #10 awg, breaker 2 pole 30 amp min.

Secondary, 2 windings wired in parallel (120V), will handle a continuous total connected load of up to 41.67 amps
Minimum size feeder wire to new panel, #6 awg copper.

Have you given any thought to surface mounting the new electrical panel in the garage? Mount on the same common wall as the main electrical panel that faces into the laundry room.
Approx how long would the branch circuits be from the new panel to the audio room? How many branch circuits are you planning to run from the new panel? 2, 3, 4?
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Thank you very much for all of the information! I could definitely mount the new sub-panel in the garage and then go straight up into the area adjoining the audio room. I currently have a 100 ft run of heavy flex conduit for my dedicated circuit; I had an electrician pull individual 5-9s copper runs for positive, negative and neutral through that new conduit 4 years ago so that part is already decided. There is only 1 dedicated audio system 20-amp circuit in the room. The dedicated circuit feeds a Purepower APS 2000 and distributes power to my entire system.
I currently have a 100 ft run of heavy flex conduit for my dedicated circuit;
09-11-12: Zephyr24069
If you put the new panel in the garage are you saying the new branch circuit/s run, from the new panel, would be 100' or more?

I had an electrician pull individual 5-9s copper runs for positive, negative and neutral through that new conduit 4 years ago so that part is already decided.
"5-9s copper runs for positive, negative and neutral through that new conduit" ??? 5-9s??
2) 120V circuits + 1) equipment ground?

Not sure what you mean..... More detailed info please.

There is only 1 dedicated audio system 20-amp circuit in the room. The dedicated circuit feeds a Purepower APS 2000 and distributes power to my entire system.
What is the end result you are aiming for from the new xfmr and new panel?
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End result is better quality power to my system; the dedicated circuit, rebalancing the house panel to make the dedicated circuit the first one off the main, all other high current circuits on the other leg/phase of the house panel, good quality wiring from the main panel to the room, cryo'ed Oyaide R1 outlets, etc... has taken me a certain amount of the distance but I'd like to separate from the house panel totally and improve the quality of power to the room even further.

individual copper runs pulled means individual insulated strands pulled through the flex conduit for positive, negative and neutral (ground)...

The run to the audio room would still need to be 100' as moving the panel to the garage would be a minimal change as the laundry room where the house panel is today is right next door to the garage; I might be able to save 10' or so but the difference is small by moving the panel. (The electrical main to the house itself is also right outside the garage and only about 20-25 feet from the existing house panel location.

Do you have your system posted? I'd like to see/know what you have going for power as you clearly have alot of experience in this area.

Thanks!
I would run a couple of dedicated 20A lines to the listening room, plug in a couple of Torus or Equi=Tech balanced power units and be done with it. I run my main system off a single 20A line, feeding three balanced isolation transformers mounted in a single large chassis, which sits near the bottom of my equipment rack. Each transformer feeds its own Oyaide R-1 duplex outlet. It is like having each component on its own dedicated line. Simple and uncomplicated, yet effective. I've been running this kind of setup for 8+ years now.
Gbart....thank you very much! If memory services the Torus units have their own isolation transformers built into them so this would accomplish more than one goal at the same time. Equitech also makes a high grade all in one panel that has an isolation transformer, EMI/RFI filtering and an isolation transformer all in the same unit; don't know what this costs but it seems like there are several ways to accomplish all this that people have utilized with great success.
BTW...in talking with an audiophile who knows a hell of a lot more than I do on this, it became clear that some of my responses and my not being an electrician have caused confusion on the thread. Apologies all around for this...
Thanks to all of you who tried to help. I've pieced together (with Arnie's help) the essential points I should be chasing if I make this modification and definitely appreciate the help!
End result is better quality power to my system; the dedicated circuit, rebalancing the house panel to make the dedicated circuit the first one off the main, all other high current circuits on the other leg/phase of the house panel, good quality wiring from the main panel to the room,

all other high current circuits on the other leg/phase of the house panel,
Sometimes that can be a bad idea. Doing so can put a strain on the secondary of the utility company's power transformer. It can also put stress on the busing and breaker connecting bus ties of the main service electrical panel.

In most residential housings areas the utility power transformer is a single phase xfmr.

The single phase secondary winding is center tapped in the middle of the winding. Thus the term split phase winding.

From the xfmr secondary to your house there are 3 power conductors.
The two hot insulated conductors connect to the outer most 240V leads of the xfmr secondary winding and the center tap conductor, the intentionally Grounded Conductor, the neutral.

To cut to the chase....

NEC code requires, as well as electricians are taught, to balance out the loads across the Lines, legs, of an electrical panel as much as possible.
Example the electrician would never put the microwave, dish washer, washing machine, sump pump, known deep freezer outlet, and the gas furnace blower motor all on the same Line, leg, in the panel.

Here is how a single phase, split phase transformer works.

Theoretically, if exactly 10 amps of load is connected across line one, L1, to neutral and exactly 10 amps of load is connected across L2 and neutral, zero amps will return on the neutral conductor back to the utility xfmr.
Only the unbalanced load will return on the neutral conductor......

The two 10 amp loads are in series with one another....
The two exactly equal 10 amp series load are actually being fed by the hot 240V legs of the panel.

Any unbalanced load will return on the neutral conductor to the source, the xfmr.

Example.

Say there are 30 amps of total connected load across L1 and neutral and only 5 amps of total connected load across L2 and neutral.

25 amps will return on the neutral conductor. The remaining 5 amps of L1 will be in series with the 5 amps of L2.... Is the balanced series load dirty or clean?
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If the main panel is evenly balanced within reason and a 5 Kva iso xfmr is connected across L1 and L2, fed 240V single phase balanced power then everybody is happy. Especially the utility power transformer.

What a good iso xfrm will give you is a new separately derived grounded AC power system. The wiring method used for the installation of the xfmr, the new electrical panel, and grounding will greatly determine its power quality performance.



http://openbookproject.net/electricCircuits/AC/AC_10.html#xtocid71230

it became clear that some of my responses and my not being an electrician have caused confusion on the thread. Apologies all around for this...
09-11-12: Zephyr24069
Zephyr24069,

For a layman I thought you did fine.

Asking questions is a good thing.
It is a hell of a lot cheaper to design the wiring methods that will give you the best results you are looking for than ending up with something you are not happy with.

Good example. You would be surprised how many audio enthusiast will hire an electrician to install a 5 Kva or 7 Kva xfmr and electrical panel.

Instead of configuring, paralleling, the secondary windings for 120V out they will series the 2 windings and feed the new panel with 120/240V.

Of course the audio enthusiast told the electrician to make sure all the branch circuits are fed from the same Line, leg, in the panel. So that is exactly what the electrician does.

Problem is only one winding of the two secondary windings is being used.
In other words each of the secondary windings of a 5 kva xfmr are good for a max connected load of 2.5 Kva.. (20.8 amps @120V)

By configuring, paralleling the two windings and feeding the new panel 120V the full 5Kva rating of the xfmr is available. (41.7 amps at 120V.)

The earth connection of the secondary conductor of the xfmr that will become the grounded conductor, the neutral, can also be an important factor. NEC code says it shall connect to the main grounding electrode system of the main electrical service.

Were the connection to the main grounding electrode system is connected can make the difference in how clean, free from AC noise the ground is and that of the neutral of the new separately derived grounded AC power system.....

I have only scratched the surface....

So don't be afraid to ask questions. Choose a good state licensed electrician that will set down with you and design the electrical system you want. He will know the code for your area and what the AHJ, authority having jurisdiction, will allow.

Just remember code is bare minimum safety standards. You can exceed the bare minimum standards.
Jim
Jea48: Thank you VERY much for all the additional information; I've learned a lot by starting this thread! The only word that comes to mind is "Wow!" concerning your level of knowledge. I will check with a good licensed electrician when proceeding with this next phase of system evolution. I'm currently starting to read alot on Controlled Power Systems and Topaz isolation transformers and SquareD (?) breaker boxes plus related topics. No rest for the wicked when it comes to the pursuit of great music listening experiences :-)