Isolated grounding of receptacles for sound equipment

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sw_ross

Senior Member
Location
NoDak
Caveat- I understand that there are different thoughts about the effectiveness of IG circuits, I'm more interested in getting a better understanding of IG because the client is asking me about installing some.

Scenario- This is all sound related. There is a 1,500 chair Ampitheater with stage that I do a lot of electrical work for. On stage there is a sub-panel that feeds various circuits for sound, lighting, and other misc props. The lighting guy was asking me about isolated ground circuits for the sound equipment because the sound guy was complaining that the lighting equipment was messing with the sound equipment.

The sub-panel is set up as you would expect. This is 208y 3-phase. The sub panel is not setup with a redundant ground. I don't do a lot of work related to IG. Questions I have:

1)Would I have to add a dedicated insulated ground wire all the way back to the G-N bonding point at the service?

2)If so does it have to be grouped with the feeders that supply this sub-panel?

3)Would that redundant ground wire have to be sized based off the breaker size that feeds the sub-panel? Or could the ground wire be smaller since it's only protecting the receptacles that the sound equipment is plugged into?

The electrical system is pretty large at this Ampitheater with a lot of sub-panels, which are fed by other sub-panels, etc. it might be challenging to get an IG insulated wire to this sub-panel.

I just wanted your thoughts before I meet with the sound guy this week.
Thanks!
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
1. Ideally, yes.

2. Yes.

3. Sized for the circuit(s) it protects. (A single #12 can protect any number of 20a circuits.)


May I suggest a different route: Try a standard (isolation) transformer for just the audio equipment.
 
FionaZuppa

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
This type of setup is done all the time w/o issue. I suspect the sound gear itself is not properly grounded, or is getting some ground loop feedback. Does taking a copper wired from sound gear chassis (EGC) directly over to the supply panel EGC make a diff? Do you have any volts between EGC and the N at the sound gear receptacle? Is the EGC a wire or is it formed by conduit? Is there any amps on the EGC wire back to panel? Is the OCPD GFI or AFI?

Audio gear cables (XLR and the like) need to be of shielded type.

But if the noise in the sound gear is 60Hz hum then most likely the sound gear is not grounded or isolated correctly. I know of no sound gear that runs directly on 120vac 60Hz, there's always some form of DC power supply in that gear. If it's external DC supply (wall warts and the like) then have them try a better DC supply to see if it makes a diff, like using a quality benchtop supply to test with. If it's internal DC supply then perhaps look at the gear make & model to make sure it's not some low-end china stuff.

I would be interested in seeing on a scope what the DC power looks like that powers the audio gear.
 
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sw_ross

Senior Member
Location
NoDak
At this time there is no equipment there yet.
It's a seasonal (summer) operation. They're going to be setting up this week.

I haven't looked too deeply into the setup. All I know is that the lighting guy says the sound guy complains about interference from his lighting (lots of led's).

Apparently the sound equipment plugged into 120v Receps from the same sub-panel that feeds the lighting. I imagine the sound is somehow hooked up to the speaker setup but I don't know yet how it all works.

He was just asking me about isolating the receptacles that the sound equipment uses.

I'll keep looking into it this week.
Thanks
 
Z

zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
FionaZuppa said:
This type of setup is done all the time w/o issue. I suspect the sound gear itself is not properly grounded,
Click to expand...

IME, that's almost always the case. Usually from using house power for the console instead of a direct run from same panel as the stage/amps. Second is an allergy to signal isolation transformers, which, contrary to some ill-informed people, aren't evil.

BTW, a properly balanced line shouldn't need to be shielded, problem is that many modern hardware use electronic drivers/receivers and they don't maintain that balance well enough; they also don't isolate so you still have a "ground-referenced" signal.

Not that I have a strong opinion about this :lol:.
 
S

sw_ross

Senior Member
Location
NoDak
This is an outside location so I’m going to guess they’re all gfci protected.
If the equipment wasn’t properly grounded and I there was current on the ground it would be tripping the gfci?
 
FionaZuppa

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
sw_ross said:
This is an outside location so I’m going to guess they’re all gfci protected.
If the equipment wasn’t properly grounded and I there was current on the ground it would be tripping the gfci?
Click to expand...

Well, if the mA is not greater than gfi trip then it wont trip. It would simply show perhaps a grounding/wiring issue.

But the gear is not even there yet.

Ok, LED lighting has all sorts of drivers involved (higher freq PWM drivers) which like CFL's can put harmonics back out onto the ckt wiring, which can then easily be picked up by op-amps in the audio gear. Putting ferrite rings on the hot legs that feed the lighting may help thwart any issues that may come from LED drivers harmonics.

Not sure there is anything to do except make sure all the grounding is good.
 
synchro

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Minimizing any common impedances in the connections between the grounds of the "interferer" and the "victim" before they are ideally connected a one point (star grounding) is a well known technique that''s effective. Also minimize the area of the "loop" between the signal conductor(s) and with the ground conductors to reduce the coupling of this "antenna". Twisted pairs and shielding help in this respect. These comments also apply to the source of interference in order to limit it from conducting and radiating noise...although the audio guy will often have more limited influence on these interferers, such as the lighting that was mentioned. If possible, extra line filters on switching supplies may be helpful. Often high frequency interference can show up in audio systems, particularly if there are any AM modulation components in the interfering signal. The semiconductors in the electronics can retify and therefore detect the AM interference just like an old Crystal Set receiver.
The stories I could tell (and also not tell) about this ;-)
 
S

sw_ross

Senior Member
Location
NoDak
So, I'm gathering that an IG system won't necessarily cure the issue? And there's a plethora of other possible issues?

If they ask me to try to isolate the ground for those receptacles I don't have an argument to steer them in a different direction, other than the idea that it might not be logistically feasible given the overall setup of the existing electrical system.
 
FionaZuppa

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
sw_ross said:
So, I'm gathering that an IG system won't necessarily cure the issue? And there's a plethora of other possible issues?

If they ask me to try to isolate the ground for those receptacles I don't have an argument to steer them in a different direction, other than the idea that it might not be logistically feasible given the overall setup of the existing electrical system.
Click to expand...

Isolated from what exactly?

Both the EGC and N are grounded wires.
 
J

Jamesco

Senior Member
Location
Iowa
Occupation
Master Electrician
sw_ross said:
Caveat- I understand that there are different thoughts about the effectiveness of IG circuits, I'm more interested in getting a better understanding of IG because the client is asking me about installing some.

Scenario- This is all sound related. There is a 1,500 chair Ampitheater with stage that I do a lot of electrical work for. On stage there is a sub-panel that feeds various circuits for sound, lighting, and other misc props. The lighting guy was asking me about isolated ground circuits for the sound equipment because the sound guy was complaining that the lighting equipment was messing with the sound equipment.

The sub-panel is set up as you would expect. This is 208y 3-phase. The sub panel is not setup with a redundant ground. I don't do a lot of work related to IG. Questions I have:

1)Would I have to add a dedicated insulated ground wire all the way back to the G-N bonding point at the service?

2)If so does it have to be grouped with the feeders that supply this sub-panel?

3)Would that redundant ground wire have to be sized based off the breaker size that feeds the sub-panel? Or could the ground wire be smaller since it's only protecting the receptacles that the sound equipment is plugged into?

The electrical system is pretty large at this Ampitheater with a lot of sub-panels, which are fed by other sub-panels, etc. it might be challenging to get an IG insulated wire to this sub-panel.

I just wanted your thoughts before I meet with the sound guy this week.
Thanks!
Click to expand...



Here are a couple of good Links.

This one has a lot more information.
PDF
Integrating Electronic Equipment and Power into Rack Enclosures

Integrating Electronic Equipment and Power Into Rack Enclosures






 
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S

sw_ross

Senior Member
Location
NoDak
FionaZuppa

FionaZuppa

Senior Member
Location
AZ
Occupation
Part Time Electrician (semi retired, old) - EE retired.
sw_ross said:
Redundant ground back to service...
Unless I'm missing something about the definition of IG?
Click to expand...

The IG I am thinking of is when you have say 48vdc comm gear in room/rack. Isolate the DC "gnd" from any AC egc, etc. Hence, all the DC gnd stuff connects together forming their own gnd plane. As example, comm chassis might have the AC egc attached to it, but the DC gnd inside stays isolated from that chassis.
 
LarryFine

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
FionaZuppa said:
Isolated from what exactly?
Click to expand...
The idea is to provide a chassis ground that is as close to earth as possible, rather than using local EGCs or conduits with possibly-noise-laden aggregate leakage currents.

Much modern electronics have no EGCs, so an IG installation would have no effect on those devices.
 
StarCat

StarCat

Industrial Engineering Tech
Location
Moab, UT USA
Occupation
Imdustrial Engineering Technician - HVACR Electrical and Mechanical Systems
Musicians Notes

Musicians Notes

FionaZuppa said:
This type of setup is done all the time w/o issue. I suspect the sound gear itself is not properly grounded, or is getting some ground loop feedback. Does taking a copper wired from sound gear chassis (EGC) directly over to the supply panel EGC make a diff? Do you have any volts between EGC and the N at the sound gear receptacle? Is the EGC a wire or is it formed by conduit? Is there any amps on the EGC wire back to panel? Is the OCPD GFI or AFI?

Audio gear cables (XLR and the like) need to be of shielded type.

But if the noise in the sound gear is 60Hz hum then most likely the sound gear is not grounded or isolated correctly. I know of no sound gear that runs directly on 120vac 60Hz, there's always some form of DC power supply in that gear. If it's external DC supply (wall warts and the like) then have them try a better DC supply to see if it makes a diff, like using a quality benchtop supply to test with. If it's internal DC supply then perhaps look at the gear make & model to make sure it's not some low-end china stuff.

I would be interested in seeing on a scope what the DC power looks like that powers the audio gear.
Click to expand...

This is an aside.
I was a Musician, having many hours of recording in a studio setting. Most savvy musicians know that most noise issues can be solved by " lifting " the ground on said piece of equipment. That is, it will stop the hum and noise coming over the speakers. One day we spent some time and found one new generation piece of equipment throwing noise back into the line. It was in fact, a Yamaha, SPX-90. What needs to be realized is that a whale of a lot of Solid State gear below the industrial market is Engineered and built very poorly, and it seems to keep getting worse. The Engineers are doing what they " can " do rather than what they should do and its because everything has been " Monetized." Would an isolated ground have worked? We never had one to try out, so I have no idea how they behave under real world field circumstances. Much about the field of Engineering since the 1980s is about them being further removed, separated, and divided from reality. As thus we have a major lot of solid state gear that is very shoddy and in the large performs very badly, and most people are running around thinking its all so cool.
This is a non-sequitur, and its time to call a spade as a spade. When large numbers of Tech people start saying no, this will be a sign that change is on the horizon.
The time wasted is colossal.
 
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