Power Mains Isolation

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sr1200

Well-known member
Joined
Dec 6, 2010
Messages
2,094
Location
Long Island, NY USA
I may be moving my studio soon (all new construction inside a house).  I had a commercial place years ago that I had built that had this big box by the mains coming from outside. (the guy I hired to do the electrical installed it knowing I was putting a studio in the building) I believe it was just a giant transformer in there (could be wrong).  But essentially, all the lines for the gear in the studio (not for the lines that had appliances (coffee machine, fridge, tv, etc.) came from that box and there was never a bit of noise, pop, crackle or thump. (miss that place).

Anyone have any idea what that thing was or have the name of something that would do the same?  Where i am now, I get the occasional hum, buzz or pop when something kicks on or off.  Not enough to be annoying, but noticeable when it happens, but I'd like the new place to be issue free if I can help (and afford) it.

Thanks as always :)
 
Almost definitely an isolation transformer. Sometimes you can buy a used one from your local power co or phone co. I have done this in the past and it saved me some money.

Jeff
 
There is lots of voodoo about mains power. Properly designed products properly wired into studios should not be sensitive to power quality, but won't stop the snake oil crowd from trying to sell thousand dollar line cords et al.

There are wiring mistakes that could cause issues. Ignoring balanced power *** for now, most modern US mains wiring is 3-wire.  #1 hot or line (120VAC) typically black. #2 Neutral (0VAC the return path for the hot line current) typically white. #3 safety ground (0V) typically green.

While both neutral and safety ground are both nominally 0V, neutral will have some small voltage on it because it is carrying the full return current coming from the line.  Safety ground is basically a back up redundant current return path in case a hot line lead accidentally touches a metal chassis that is grounded.  The safety ground path is supposed to carry enough current to trip the fuse/circuit breaker without exposing meat puppets to dangerous voltage while waiting for the breaker to break.

In the audio world there is a lot of confusion about audio grounds and equipment safety grounds. It is common practice to bond equipment metal chassis to safety ground and further to tie wire shields to chassis ground, but this is never to be confused with audio 0V (I refuse to call it audio ground).

For a greenfield studio project the important thing is to make sure all outlets are wired to code taking care that neutral currents do not corrupt safety grounds (neutral and ground only connect together back at the breaker panel.) 

Properly designed gear, operated from properly wired outlets should be fine. (Note: some legacy gear is not properly designed.)

For an extra degree of caution, a separate branch can be provided for appliances, copy machines and the like.

JR

**** balanced power, is a clever solution to what should not be a problem. Typical mains power is one 120VAC conductor with a 0V return. Balanced power breaks up the 120V into a  60VAC line and opposite polarity 60VAC neutral return.  The equipment does not know the difference between 120V and 60V+60V, BUT and the whole claim to fame about balanced power is that opposite polarity mains power waveforms will cancel or neutralize interference fields.  On top of that 60V mains power should cause less interference than 120V.  I repeat for well designed gear, with decent wiring this should not make a difference. Some consumer (semi-pro) gear with two wire line cords ASSume that neutral is 0V and cap couple that to chassis for lower hum levels. With balanced power the neutral now has 60VAC on it, not exactly a quiet shield ground.  YMMV
 
JR, I hear what you're saying, and I agree that most "modern" construction would fit that bill, however, where I'd be going was build in 1952 and I've already seen a bunch of the outlets without ground and I'm not sure if a complete rewire of the place is in the budget.  (plumbing on the other hand... its all gotta go).  I have line conditioners in the rack, but honestly, i kind of feel like they're just rack mounted power strips. 

If i have new lines added to the box for the gear, and i get noise or issues, would it be easy enough to add the isolation "box" after the fact or should i just say F it and do it from the get go?
 
sr1200 said:
If i have new lines added to the box for the gear, and i get noise or issues, would it be easy enough to add the isolation "box" after the fact or should i just say F it and do it from the get go?
Drawing a clean 3-wire line is the 1st thing to do; I would say 9 times out of 10 it fixes most issues. Iso xfmr can be added later - just be careful of its position because it radiates serious magnetic field.
Sometimes it's just one piece of gear that creates problems on the whole installation. You may want to re-connect your system one piece at a time and hopefully find the culprit (very often something with unbalanced connections).
 
sr1200 said:
JR, I hear what you're saying, and I agree that most "modern" construction would fit that bill, however, where I'd be going was build in 1952 and I've already seen a bunch of the outlets without ground and I'm not sure if a complete rewire of the place is in the budget.  (plumbing on the other hand... its all gotta go). 
Plumbing has to work...

I can only bloviate about electricity "should" do.

I am a big advocate for proper (3 wire) mains power wiring... (In my house I have jury rigged added ground wires for kitchen and laundry room), more for safety than noise abatement.
I have line conditioners in the rack, but honestly, i kind of feel like they're just rack mounted power strips. 

If i have new lines added to the box for the gear, and i get noise or issues, would it be easy enough to add the isolation "box" after the fact or should i just say F it and do it from the get go?
You mention this is a residence. Have you looked at your power transformer?  Years ago I had my own power transformer, but after hurricane Katrina snapped my power pole on two,  I have been piggy backed on the same transformer as two neighbors.

Power quality in industrial buildings can problematic, even apartments with big elevators and related machinery can have issues. In a residence I would expect most noise to be from your own appliances and modest (unless you are sharing a transformer with a machine shop next door).

It might be instructive to search for an architectural spec from a big dog studio designer, and talk to other studio builders. The only studio I was even peripherally involved in (when Peavey upgraded their auditorium to house an audio/video studio) used a professional studio design firm, and I was not even slightly involved.

Have you tried it as is?  I am not a huge fan of band aid power conditioners either. If you have your own transformer your power coming in is probably OK... Maybe just rewire a branch to the studio, or two to keep the clean and dirty power users on separate branches.

JR
 
The problem with power conditioners is they work well only if they are connected to a clean earth, which is also the foremost condition for a clean system. So in any case you need to draw a clean earth, then while you're at it, it's not much more work to draw a full 3-wire line.
 
For me this has always been the bible of the installation !



http://www.prosoundweb.com/channels/av/newly_republished_audio_systems_design_and_installation_by_philip_giddings/
 
Remember that with an isolation transformer, you must provide a safety ground on the isolated side. The transformer primary is across incoming hot and neutral, and as JR notes the neutral is bonded to safety ground at the panel. The secondary provides a galvanically-isolated hot and neutral but there's no safety ground. You must provide that ground, and among other things it ensures that the isolated side neutral doesn't float above the ground.
 
Andy Peters said:
You must provide that ground,
Agreed.


and among other things it ensures that the isolated side neutral doesn't float above the ground.
Does it? With a floating secondary (and properly earthed apparatus), parasitic capacitances will make the neutral floating at a more or less significant fraction of the mains voltage, out-of-phase with the Live conductor. If connected with apparatus equipped with XY caps, the secondary voltage will be pretty close to +/-58Vac. Touching any of the Live or Neutral connectors would be essentially harmless.
In terms of noise generated inside the equipment, it should be better, and in no case worse. In this respect, it would be equivalent to balanced power.
 
Three reference papers:

The Middle Atlantic white paper:
"Integrating Electronic Equipment and Power into Rack Enclosures"
'Optimized Power Distribution and Grounding for Audio, Video and Electronic Systems'
Power Distribution and Grounding of Audio, Video and Telecommunications Equipment White Paper
http://www.middleatlantic.com/resources/white-papers.aspx

From Jim Brown:
"Power and Grounding For Audio and Audio/Video Systems"
' A White Paper for the Real World'
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

From the Bill Whitlock seminar notes:
"An Overview of Audio System Grounding & Interfacing"
9/4/2012
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

 
Hey JR-do things change in a commercial space with 3 phase power?  I'm just curious if the difference in phase of different branches coming from the breaker box would create any special considerations (like making sure only the same phase branches end up in the control room, etc).  I'm just curious because I'm in a warehouse with 3 phase power and I had never really considered that while putting in new circuits.
 
Mbira said:
Hey JR-do things change in a commercial space with 3 phase power?  I'm just curious if the difference in phase of different branches coming from the breaker box would create any special considerations (like making sure only the same phase branches end up in the control room, etc).  I'm just curious because I'm in a warehouse with 3 phase power and I had never really considered that while putting in new circuits.
I expect the larger concern is about industrial machinery drawing heavy currents.

Well designed equipment is not very sensitive to mains power.

Proper 3 circuit (Line, Neutral, Ground) wiring should be adequate...    For gear that has poor mains rejection, you might want to avoid an unusually noisy phase.

JR
 
Mbira said:
do things change in a commercial space with 3 phase power?  I'm just curious if the difference in phase of different branches coming from the breaker box would create any special considerations (like making sure only the same phase branches end up in the control room, etc).  I'm just curious because I'm in a warehouse with 3 phase power and I had never really considered that while putting in new circuits.
It is common practice to use only one dedicated phase for the complete studio installation; however the most significant factor is having a dedicated 3-wire line. In live sound, it's usual to have one phase for light, one for sound, and one for machinery. If one of the pieces of equipment (usually the dimmers) produces garbage on the line, it won't make thing better, because trash pollutes the neutral. Things are much better now with the increasing use of LED's. In a studio environment, that should not be a major issue; anyway, I would avoid dimmers at all cost. At Barclay Studios, we had the luxury of having lighting on remote-controlled Variacs!
 
As usual, John's explanation is spot on. However, this quote must be clarified:

"For a greenfield studio project the important thing is to make sure all outlets are wired to code taking care that neutral currents do not corrupt safety grounds (neutral and ground only connect together back at the breaker panel.)  " 

The grounding conductor is only bonded to the neutral  conductor at the service main disconnect, which may or may not be a breaker panel.  The two must remain separated throughout the rest of the system, even in a sub-panel.
 
Also 3 phase can be created from what's called a wild leg which when comparaed to neutral runs I believe 180 v so can not be used to derive the 120v .  This is easy to confirm with a meter.  In the facility I'm familiar with the wild leg is marked with orange tape as well and is only used for the 220/208 leg when compared to the other two legs.
 
Yes, wild leg or high leg delta and maybe red dog delta, are used to get 120V single phase from a 3 phase system. More popular a few decades ago.  Jim Brown sometimes writes about the noise problems that they cause.
 
sr1200 said:
I may be moving my studio soon (all new construction inside a house).  I had a commercial place years ago that I had built that had this big box by the mains coming from outside. (the guy I hired to do the electrical installed it knowing I was putting a studio in the building) I believe it was just a giant transformer in there (could be wrong).  But essentially, all the lines for the gear in the studio (not for the lines that had appliances (coffee machine, fridge, tv, etc.) came from that box and there was never a bit of noise, pop, crackle or thump. (miss that place).

Anyone have any idea what that thing was or have the name of something that would do the same?  Where i am now, I get the occasional hum, buzz or pop when something kicks on or off.  Not enough to be annoying, but noticeable when it happens, but I'd like the new place to be issue free if I can help (and afford) it.

Thanks as always :)

Easiest solution is to get an electrician to run a few dedicated 120v/20a circuits, done deal!  Chances are if the entire unit is wired for only 120v then the lighting circuit can be tied in with those outlets and being that it's a commercial unit more than likely you probably have those old fluorescent lighting fixtures which is what could more than likely be causing that hum and noise.  There is no telling what else could be wired on the branch circuit along with the outlet you're currently using. 

 

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