Need help solving a sound issue (lights causing bass & guitar buzzing)

[Pings Bass]

The last church I played regularly at had terrible AC hum. All their wiring was totally janky. I don't think anything short of running a generator out the back door for my bass rig would have helped. We muddled through, somehow.

 

[clockworkcorpse]

I spoke to one audio engineer today who suggested I try putting an Ebtech Hum X Ground Loop Hum Eliminator on the sound mixing console’s power. Would that be worth purchasing, to try?

from the description it sounds like it uses a transistor that needs a particular voltage to make the ground connection, but if that voltage is not met, it keeps the ground "lifted" ...

I suspect (but do not know) that the problem is related to the LED lights and their power supplies. the drivers on LED lamps turn themselves on and off rapidly to regulate the voltage, like a switching power supply. every time they switch off, there is a tiny reflection of the sine wave that bounces back. this happens very rapidly, and is known as "harmonics" and is serious trouble with some equipment. this does not happen on the ground, but on the hot wire. unfortunately a " hot lift" is not possible for obvious reasons, and harmonics will spread to across all ccts this side of the last step down transformer (the big thing on the pole outside), but an isolation transformer does not let harmonics through.

as suggested before, the isolation transformer and gfci receptacle with ground defeated (right before the receptacle, the receptacle itself does a better job of tripping in an emergency than the cct breaker) will isolate everything going to your bass, but will not help with electromagnetic interferance.

i'd love to be able to help more, i'm sorry if my responses are not helpful, i'm genuinely curious though about these problems.

 

[Rabidhamster]

Wall dimmers are just awful sources of hum.

Unfortunately there are quite a few other culprits. Are the LED ballasts switch mode? It is still possible to get transformer based LED drivers and those can put out noise also.

I’d probably try the lights independent of controller, just plugging in if you’re able, and see if that changes anything.

I’d think separating house lights from stage lights to be a necessity.

Also since your bass buzzes more facing one direction you may be able to wander around and find the Point source of the stage interference.

fwiw I have personally run a 250 watt switchmode LED driver (ballast) on the same outlet as a tube amp, at the same time, with no noise.

 

[Wasnex]

I spent a week trying to fix this exact problem in a local church a few years ago. Even though I found that the person that soldered the xlr connectors on both ends of the cables from the stage to the sound room had the wires on the wrong pins and corrected it, the hum was still there only not nearly as bad. I even replaced the mixer console that was damaged due to the improper wiring. (The ground isolation circuit was damaged.)

I consulted with the electrician that wired the building and tried in vain to get him to understand that all of the plugs used on the stage and the ones in the sound room needed to be on a dedicated ground not shared with anything else. I also pointed out that these circuits needed to be on the same phase in the electrical panel. His reply was that this building was three phase and that it is allowed by code to share neutrals or grounds with other circuits. I again tried to make him understand that this is not acceptable for audio equipment. I went to the breaker panel myself and rearranged some of the breakers to get them on the same phase. That helped a little.

They have a bank of 4 light dimmers in the same room with the sound board that are connected to 8 chandeliers in the sanctuary. If I turned those lights off the hum went away. (Because of the shared neutrals or grounds.) If those lights were on and the dimmers were turned all the way up there was still a slight hum but not untolerable. If these lights were dimmed the hum got louder as the amount of dimming increased. When I brought this problem to the church council and explained about the shared wiring the electrician got angry and told them that he would have to rip out a lot of walls to rewire the entire sanctuary and stormed out of the meeting. He was also a member of this church, but he did not return for nearly a year.

It sounds to me that you may have a similar issue that will not be easy to fix... Good luck...

Let me start by saying I am not a subject matter expert or an electrician. I do have a background in electronics, but it's been a long time since I studied power distribution and I did not study it much.

If I understand, putting the audio and lighting on it's own phase can help some with the noise in some circumstances, but it won't totally kill the problem because all of the phases share both a neutral bus bar and the ground bus bar at the panel. Also if two phases are pulling significantly different amounts of current it can actually exacerbate the problem. Ideally the phases should be balanced or I believe it puts a voltage potential between the neutral and ground, which causes hum.

It don't think it's necessary to rip up walls to resolve a grounding issue. Instead you probably need a separate service with a dedicated ground for the audio circuits. Usually performance venues install a separate service with a disconnect and use some sort of power distribution system instead of plugging into the walls.

I toured for a couple of decades and we often traveled with a power distribution system made by Motion Labs. We had it wired up so we could tie into a disconnect with either pig tails or cam locks, or (in an emergency) we could plug into three 20A wall circuits. A licensed electrician was required to make the connection to the disconnect.

Here are some images from motion labs.

This has 5 wire camlocks to tie into the disconnect. The white plugs are four wire Hubbel twist lock connectors. Each carries three phase of power and you can see circuit breakers to the left.

The power can be routed to and through this sort of module.

The plugs on the front are courtesy outlets. The back also has several plugs. These go in 19" rolling racks so the amps and other gear are permanently plugged into the module. Just connect the modules and flip a few switches and you are read to go.

We also had modules that were used as stage boxes

We ran a long extension to our mixing console and FOH racks that was gaff taped to our snake. In a church, if there is cable trench you could pull an extension. If not, I think an electrician should be able to run a single circuit of clean power without totally destroying the facility.

Motions labs is pretty much top of the line. I used it as an example because that is what I am familiar with. There are less expensive distribution systems. But IMHO, if the power is getting dirtied up by the lights, you need a dedicated service that is earthed separately from the lights.

If the problem is EMI I don't think resolving grounding issues will solve the problem. This may be where the grounded conduits for the lighting gear is more important.

Unfortunately this is a complex problem that is difficult/expensive to solve.

Good luck!

 

[clockworkcorpse]

@Wasnex good point on the shared neutral across phases, harmonics is shared between phases this way. places with big computer installations or lots of ballasted lights use a big isolation transformer to keep that interference away from other loads, that's why I keep thinking the isolation transformer just for the musical gear would keep whatever dirty electrons off the tone, as it creates it's own hot and neutral that is electrically isolated from everything else in the building. I wonder what's inside your magic box...

 

[Richard Martin]

Here's a good read on the EMF created by 120 volt AC LED lights. It's a whole lot of hum...

Low Electromagnetic Emissions Office Equipment - LED light bulbs electromagnetic emissions

 

[Wasnex]

@Wasnex good point on the shared neutral across phases, harmonics is shared between phases this way. places with big computer installations or lots of ballasted lights use a big isolation transformer to keep that interference away from other loads, that's why I keep thinking the isolation transformer just for the musical gear would keep whatever dirty electrons off the tone, as it creates it's own hot and neutral that is electrically isolated from everything else in the building. I wonder what's inside your magic box...

Pretty sure the Motion Labs gear is just wire, breakers, and connectors. No tricks or magic, just heavy-duty power distro.

I believe the big touring companies generally run separate distros on separate disconnects for audio and lighting.

I have never used an isolation transformer, but I do believe one may be effective in reducing problems between hot and neutral.

However if the problem is a noisy ground, I suspect this may not totaly solve the problem since the ground passes through.

If I understand, you suggested leaving the ground disconnected on the secondary of the transformer, but using a GFCI for safety. Way beyond my expertise to say this would be safe in all circumstances or comply with electrical code.

Normally the audio console functions as sort of a central signal ground for all connected equipment, so there may be a range negative consequences for lifting the ground on the console.

 

[bwildt]

Consumer dimmers are notorious for causing hums and interference.

 

[BooDoggie]

Did you guys ever rewire the sanctuary? And man, this electrician fellow is a piece of work.

Unfortunately, no they never did any additional work after I left... I got the hum down to a almost imperceivable level unless the lights were dimmed. I did, as @Wasnex has suggested, tell them that they might try running a long extension cord from a plug on the stage through an unused conduit that runs under the floor to the mixer room that may eliminate the shared neutral issue. The stage and mixer room are attached to a separate breaker box, but I'm not really sure if it is isolated from the main three phase grounds.

These people paid me a lot of money to "help" them with their sound as well. But when I suggested that they were hearing more reflected sound than the direct sound and that they should install acoustical treatments on the walls and possibly hang some from the hardwood ceiling it was the same story. I was told that they did not want to mount anything on the walls... Ya gotta love church people logic... The way the room looks is much more important than the way the music sounds.

 

[dkelley]

When in doubt, a REALLY long VERY heavy gauge extension cord to power your amp from an entirely different part of the church - way in the back, or down the hall or whatever... that might be just what the bassist ordered.

That's gonna be expensive, mind you, unless you have one kicking around. And of course....some bratty kid or stupid person comes along and unplugs you from way down the hallway while you're playing...

 

[clockworkcorpse]

@Wasnex i'm an electrician in canada, so I don't know what other countries allow, but for portable equipment in cases "where reliable grounding cannot be obtained" it is legal to use a GFCI in place of bonding. cec10-408(4). the definition of reliable grounding is vague though. section 26 of the code also allows us to permanently install GFCI receptacles in locations that do not have a bonding conductor, like in a house that did not have it's device boxes bonded. generally speaking, GFCI protection is safer and operates faster than the cct breaker, but the code wishes us to bond to ground whenever possible.

the box I will one day build and test (once I have salvaged the right bits for it, haha) would not be legal to use though, because every device needs to be approved by the canadian standards association before it could be used, and defeating the bond to ground would not go over well. it's one of those situations where if you understand how things work, it can be made perfectly safe, even if it is not legal. unlike pulling the ground prong off an extension cord, but that's another story.

edit: oh, and the box itself would be bonded to ground, as would the isolation transformer, it would just be the gfci receptacle(s) that would be isolated. so whatever is plug in gets all three isolated, but the box itself is still safe.

i've heard legends of travelling shows running their own ground wire themselves and pounding a ground rod into the dirt outside.

it is not legal here to run an extension cord through conduit, or to permanently install an extension cord. extension cords cause fires. check that fact with the office of the fire commissioner.

 

[sawzalot]

Who needs lights? Shut them off.

 

[byacey]

Who needs lights? Shut them off.

Acetylene Lamps, they don't produce any EMI.
If the house lighting is LED, it's possible the phase control dimmers weren't designed for such loads, but rather for incandescent. Triac or SCR dimmers can radiate a lot of noise from the cabling that feeds the lamps, but they can also reflect a lot of noise back into the AC supply source. The Strand dimmers I used to work on had big torroidal chokes to to minimize the high frequency spikes that are generated when the triacs turn on and off.

The noise is usually worst at about 50% power / 90 degrees of phase where the instantaneous current is highest as the triac gets switched on.

Edit: That's the cause of the noise- Finding the fix will come down to determining if the noise is from the load side or the supply side of the switching triacs. Ideally, all the supply and load wiring should be in grounded steel conduit which offers considerable EMI shielding, compared to aluminum armoured BX cable. As well, the dimmers should have sufficient chokes. If the lighting system is lacking either of these two things, chances are anything else is a waste of time.
P.S. When I built my recording studio, I installed variac dimmers for all the lighting that I wanted dimming. This turned out to be a good choice, as I've never had any noise issues.

 

[Wasnex]

@Wasnex i'm an electrician in canada, so I don't know what other countries allow, but for portable equipment in cases "where reliable grounding cannot be obtained" it is legal to use a GFCI in place of bonding. cec10-408(4). the definition of reliable grounding is vague though. section 26 of the code also allows us to permanently install GFCI receptacles in locations that do not have a bonding conductor, like in a house that did not have it's device boxes bonded. generally speaking, GFCI protection is safer and operates faster than the cct breaker, but the code wishes us to bond to ground whenever possible.

the box I will one day build and test (once I have salvaged the right bits for it, haha) would not be legal to use though, because every device needs to be approved by the canadian standards association before it could be used, and defeating the bond to ground would not go over well. it's one of those situations where if you understand how things work, it can be made perfectly safe, even if it is not legal. unlike pulling the ground prong off an extension cord, but that's another story.

edit: oh, and the box itself would be bonded to ground, as would the isolation transformer, it would just be the gfci receptacle(s) that would be isolated. so whatever is plug in gets all three isolated, but the box itself is still safe.

i've heard legends of travelling shows running their own ground wire themselves and pounding a ground rod into the dirt outside.

it is not legal here to run an extension cord through conduit, or to permanently install an extension cord. extension cords cause fires. check that fact with the office of the fire commissioner.

Thanks for the expanded explanation on the isolation transformer and how the ground lift and GFI would work.

Regarding the extension chord, I wasn't suggesting running it through conduit. Many venues have an under floor trench for cable runs. A big problem with extension chords is most layman don't know how to determine the gauge of wire that is required and how long of a run the chord is good for. AFAIK, longer runs require heavier gauge wire, so you start getting into trouble when you connect multiple small gauge extension chords end to end.

I don't know what the electrical code allows here in the US, or what would be construed as permanent. Audio equipment is often mobile in nature. You might set up a board for an extended time in one location, but it's not really installed, so is in permanent? Obviously not an argument you want to get into with the Fire Marshall.

We ran Motion Labs cables with Hubble Twist locks and circuit breakers on both ends with some of our systems, so not really an extension chord, but I do think I remember one venue that refused to let us run power through the cable run because the Fire Marshall had told them it was not allowed. It was not a problem because they had an audio station built with good power.

If dragging an extension through the cable run is of concern with the local Fire Marshall, then appropriate wire and conduit could be installed to code. Pretty sure, conduit is required for exposed wiring in the US.

 

[Killens84]

Thank you for all the great info. I think we’re going to have to just hire a professional to come in and fix the issue. Neither I nor anyone on the staff is knowledgeable enough in this stuff to go in and fix it.

 

[agedhorse]

I spent a week trying to fix this exact problem in a local church a few years ago. Even though I found that the person that soldered the xlr connectors on both ends of the cables from the stage to the sound room had the wires on the wrong pins and corrected it, the hum was still there only not nearly as bad. I even replaced the mixer console that was damaged due to the improper wiring. (The ground isolation circuit was damaged.)

I consulted with the electrician that wired the building and tried in vain to get him to understand that all of the plugs used on the stage and the ones in the sound room needed to be on a dedicated ground not shared with anything else. I also pointed out that these circuits needed to be on the same phase in the electrical panel. His reply was that this building was three phase and that it is allowed by code to share neutrals or grounds with other circuits. I again tried to make him understand that this is not acceptable for audio equipment. I went to the breaker panel myself and rearranged some of the breakers to get them on the same phase. That helped a little.

They have a bank of 4 light dimmers in the same room with the sound board that are connected to 8 chandeliers in the sanctuary. If I turned those lights off the hum went away. (Because of the shared neutrals or grounds.) If those lights were on and the dimmers were turned all the way up there was still a slight hum but not untolerable. If these lights were dimmed the hum got louder as the amount of dimming increased. When I brought this problem to the church council and explained about the shared wiring the electrician got angry and told them that he would have to rip out a lot of walls to rewire the entire sanctuary and stormed out of the meeting. He was also a member of this church, but he did not return for nearly a year.

It sounds to me that you may have a similar issue that will not be easy to fix... Good luck...

You may have caused a serious and dangerous neutral overload situation by rearranging breakers on a system that (legally) uses shared neutrals (either single or three phase). You need to get the electrician back and have them correct what you did before you have MUCH bigger problems.

Your electrician was absolutely correct that it's legal for branch circuits on dissimilar phases to share neutrals AND there is nothing in this situation that will cause any noise. It's done all the time in theatres, arenas, recording studios and churches, without noise problems.

You use the term "dedicated ground", which is meaningless. All (legal) grounding wires are dedicated grounds. What I think you meant to say is "isolated ground" which is entirely different and depends on an engineered system of defined and routed ground paths independent of and isolated from the rest of the building's grounding system (grounded conduit, plumbing piping, gas piping, CATV, building steel and earth ground) except at the designated and defined IG panelboard. There in in effect 2 grounds, and the receptacles used have the yoke ground separate from the 3rd pin U ground. This needs to be designed and installed by professionals.

What you did was wrong, the electrician was 100% correct, and IMO you disrespected the electrician by doing something foolish and dangerous to others. It may also be illegal depending on the jurisdiction and if the damage causes a fire (the most likely result), could result in criminal charges as well. (IMO) You owe the man a sincere apology, and find a way to make it right before somebody gets hurt.

Out of curiosity, why did you think this was a good idea, where in the world did you get this idea from, and why would you of all things go behind a licensed professional's back and change their work? Also, why would a church allow somebody to change a safety related item that they paid to have installed (and presumably inspected)? All I can say is wow, my mind is blown.

And yes, I am an EE and I spent much of my professional career designing power systems for entertainment industry venues (including churches, which was rarely entertaining). There is a reason we go to school and get tested and licensed, this is a good example.

 

[agedhorse]

The only one of those I know the answer to, is yes, they have two dimmers... The wall plate by the entrance to the room, and the lighting console in the A/V balcony. I believe they turn off the wall plate dimmers before using the lighting console to run the house lights. It was the console in the A/V balcony that we were using when we found that turning the house lights all the way down cleaned up the buzzing.

I’ll have to check on the LED lights, to see if they’re rated to be run from dimmers. And I’m not sure about the load circuits in grounded conduit. That one is beyond my understanding. Would an electrician need to determine that?

There should only be one dimmer as interaction between the phase control circuits can cause mis-firing due to the second dimmer's sync circuits becoming unstable. Rule number 1 is only to use a single dimmer. Rule number 2 is to be sure that the load is rated for dimming. Rule number 3 is to be sure that the LED lights have been FCC tested for compliance to Part 15B (this applies for Canada too, as they share this standard)

Wow, that’s interesting. We had all the grounds checked in the audio paths, and they all checked out ok. But I’m not sure if the stage and mixing booth have a dedicated ground just for the audio. And I’m not sure about the phase.
The XLR cables checked out ok, and the mixer board (Behringer X32) was just purchased about a year ago.
I had an electrical engineer friend of mine come in and check some of this stuff, but audio isn’t his area of expertise. His job deals more in automation for various companies. We may have to bring in someone who does audio installs for churches.

It has nothing to do with the phase, it may be due to the LED lighting and/or the inclusion of ground loops due to multiple ground connections where only one U ground path is allowed. Generally, ground loops within the audio ground (say from a bass amp) can be effectively handled by the amp's direct output ground lift switch (that's why we put these switches on the amp's DIs)

Did you guys ever rewire the sanctuary? And man, this electrician fellow is a piece of work.

Actually, the electrician is spot on correct. You mis-identified the "piece of work" IMO.

I do need to bring this up though: different ccts do not isolate loads from each other unless they are on different phases. so it makes sense to have all audio equipment on a different phase from lighting equipment. isolation transformers can do this as well, but they usually don't isolate the ground, because the ground is the most important safety feature of any electrical installation and breaking it can cause death if another fault develops.

No it does not matter. Tell me how ANY of the equipment can identify what phase it's on, because every piece of equipment used in audio is already transformer isolated, and NOTHING from the primary (hot or neutral) connects to the chassis other than through an approved capacitor with a very small leakage current (typically less than 1mA).

Isolation transformers do not isolate the ground in any legal installation of this type, the secondary of the isolation transformer operates from the principle of a derived ground, where bonding between neutral and ground is re-established.

I don't have a problem like this, but if I did, I would wire a small isolation transformer to the end of a cord, and wire a gfci receptacle to the load side of the isolation transformer but leave the ground disconnected from the gfci. the isolation transformer creates a new hot and neutral that is not electrically connected to any other loads, and the gfci provides the same protection as the ground without having that connection. this should eliminate any noise on the wires, but not in the air. i'd love to be able to test this contraption, but I don't have a situation to correct...

Why would you come up with this solution when you (and I) don't even have the slightest idea what the actual CAUSE is? Without correctly identifying the cause, any solution like this is nothing more than a wild ass guess, that in the hands of a "tinkerer" is dangerous if nothing else.

one super important issue, specific to @BooDoggie : when neutrals are shared, it is not safe to put any loads on the same phase. with a four wire cct from a three phase panel, the three hot wires need to be out of phase with one another, so that each phase uses the shared neutral "in a different direction" (this is hard to simplify, but separate phases will cancel each other out somewhat on the neutral, resulting in the difference in current travelling on that one wire). if two ccts from one phase share a neutral, the currents on each cct are somewhat added, and that can result in exceeding the current rating for the wire. this can cause excessive heat and insulation failure that might not be noticeable immediately unless it's measured.

in a single phase panel, for example, two ccts from different phases sharing a neutral with 8 amps of current on each cct will result in zero current on the neutral, however, two ccts with 8 amps each from the same phase sharing a neutral will result in 16 amps on the neutral. it works similarly with three phase, but the balance happens three ways.

so if a building is wired with shared neutrals, it can be extremely dangerous to move ccts around the phases unless you know exactly what you are doing.

This is absolutely correct.

I spoke to one audio engineer today who suggested I try putting an Ebtech Hum X Ground Loop Hum Eliminator on the sound mixing console’s power. Would that be worth purchasing, to try?

Not without identifying the actual problem first, in this case I doubt it. Just another wild ass guess.

I suspect (but do not know) that the problem is related to the LED lights and their power supplies. the drivers on LED lamps turn themselves on and off rapidly to regulate the voltage, like a switching power supply. every time they switch off, there is a tiny reflection of the sine wave that bounces back. this happens very rapidly, and is known as "harmonics" and is serious trouble with some equipment. this does not happen on the ground, but on the hot wire. unfortunately a " hot lift" is not possible for obvious reasons, and harmonics will spread to across all ccts this side of the last step down transformer (the big thing on the pole outside), but an isolation transformer does not let harmonics through.

WHY would such harmonics be generated in the first place by a legal piece of gear? There is something wrong, identifying the problem BEFORE proposing a solution makes so much more sense.

@Wasnex good point on the shared neutral across phases, harmonics is shared between phases this way. places with big computer installations or lots of ballasted lights use a big isolation transformer to keep that interference away from other loads, that's why I keep thinking the isolation transformer just for the musical gear would keep whatever dirty electrons off the tone, as it creates it's own hot and neutral that is electrically isolated from everything else in the building. I wonder what's inside your magic box...

Again, identify the problem first. In the hundreds of installations that I designed, installed or inspected, I very rarely (if ever) saw an installation where an isolation transformer provided a meaningful decrease in noise floor. A properly designed isolated ground installation can certainly help with the reduction of ground loop noise by minimizing the circulating currents from leakage throughout the entire electrical system, but this is not what you are proposing (nor may it be the cause either).

The stage and mixer room are attached to a separate breaker box, but I'm not really sure if it is isolated from the main three phase grounds.

The grounds must NEVER EVER be isolated from the main ground, and in fact it is required by code for there to be a single bonding point at the main service entrance point where the protective ground, the neutral, the building steel, water piping, gas piping, TELCO, CATV, satellite and any required earth rods/planes are all bonded together.

These people paid me a lot of money to "help" them with their sound as well. But when I suggested that they were hearing more reflected sound than the direct sound and that they should install acoustical treatments on the walls and possibly hang some from the hardwood ceiling it was the same story. I was told that they did not want to mount anything on the walls... Ya gotta love church people logic... The way the room looks is much more important than the way the music sounds.

Hopefully your sound advice was better than your electrical advice. At least you can't generally kill people with sound, though hopefully you didn't handle the rigging.

Thank you for all the great info. I think we’re going to have to just hire a professional to come in and fix the issue. Neither I nor anyone on the staff is knowledgeable enough in this stuff to go in and fix it.

The best conclusion IMO on a train wreck of a thread. You will need an experienced industry pro who understands power distribution as well as how noise gets generated and distributed through an installation. QUALIFIED electrical experience will be a necessary part of this IMO.

I hear people griping about why there are codes and why they are so strict and don't make any sense. Actually, they make all the sense in the world, they have improved the electrical safety by a factor of 100 or more over the last 100 years. I think this thread reinforces why the codes exist, codes (regulations) attempt to protect ordinary people using buildings from stupid things done by those who don't understand. Safety really is important and a big deal.

 

[byacey]

Acetylene Lamps, they don't produce any EMI.
If the house lighting is LED, it's possible the phase control dimmers weren't designed for such loads, but rather for incandescent. Triac or SCR dimmers can radiate a lot of noise from the cabling that feeds the lamps, but they can also reflect a lot of noise back into the AC supply source. The Strand dimmers I used to work on had big torroidal chokes to to minimize the high frequency spikes that are generated when the triacs turn on and off.

The noise is usually worst at about 50% power / 90 degrees of phase where the instantaneous current is highest as the triac gets switched on.

Edit: That's the cause of the noise- Finding the fix will come down to determining if the noise is from the load side or the supply side of the switching triacs. Ideally, all the supply and load wiring should be in grounded steel conduit which offers considerable EMI shielding, compared to aluminum armoured BX cable. As well, the dimmers should have sufficient chokes. If the lighting system is lacking either of these two things, chances are anything else is a waste of time.

You may have caused a serious and dangerous neutral overload situation by rearranging breakers on a system that (legally) uses shared neutrals (either single or three phase). You need to get the electrician back and have them correct what you did before you have MUCH bigger problems.

Your electrician was absolutely correct that it's legal for branch circuits on dissimilar phases to share neutrals AND there is nothing in this situation that will cause any noise. It's done all the time in theatres, arenas, recording studios and churches, without noise problems.

You use the term "dedicated ground", which is meaningless. All (legal) grounding wires are dedicated grounds. What I think you meant to say is "isolated ground" which is entirely different and depends on an engineered system of defined and routed ground paths independent of and isolated from the rest of the building's grounding system (grounded conduit, plumbing piping, gas piping, CATV, building steel and earth ground) except at the designated and defined IG panelboard. There in in effect 2 grounds, and the receptacles used have the yoke ground separate from the 3rd pin U ground. This needs to be designed and installed by professionals.

What you did was wrong, the electrician was 100% correct, and IMO you disrespected the electrician by doing something foolish and dangerous to others. It may also be illegal depending on the jurisdiction and if the damage causes a fire (the most likely result), could result in criminal charges as well. (IMO) You owe the man a sincere apology, and find a way to make it right before somebody gets hurt.

Out of curiosity, why did you think this was a good idea, where in the world did you get this idea from, and why would you of all things go behind a licensed professional's back and change their work? Also, why would a church allow somebody to change a safety related item that they paid to have installed (and presumably inspected)? All I can say is wow, my mind is blown.

And yes, I am an EE and I spent much of my professional career designing power systems for entertainment industry venues (including churches, which was rarely entertaining). There is a reason we go to school and get tested and licensed, this is a good example.

I installed systems in some Performing Arts theaters, three in Alberta, and one in the dead of winter in Saskatchewan, -40C and all. I remember the one in Saskatchewan well because The grim reaper was close on my heels that day; A rigger working in the fly tower dropped a crescent wrench that should have been tied off, and it hit the floor about a foot from where I was soldering up some xlrs in the stage wings. I grabbed the wrench and charged up the stairs to the fly tower, but the culprit was long gone. I kept the wrench as reminder of God watching over me that day. Besides, it was a good Bahco wrench, made in Sweden; it has a special place in my tool box.

In all these theaters they used what was called "technical ground" for the sound equipment. It was essentially a huge ground grid buried at considerable depth into the soil, before the concrete floor of the house was poured. This ground was completely isolated from all other safety electrical grounds in the building, and was only used for the audio gear. I never looked into it, but they may have been using transformer balanced power for the audio gear as well.

 

[agedhorse]

When

I installed systems in some Performing Arts theaters, three in Alberta, and one in the dead of winter in Saskatchewan, -40C and all. I remember the one in Saskatchewan well because The grim reaper was close on my heels that day; A rigger working in the fly tower dropped a crescent wrench that should have been tied off, and it hit the floor about a foot from where I was soldering up some xlrs in the stage wings. I grabbed the wrench and charged up the stairs to the fly tower, but the culprit was long gone. I kept the wrench as reminder of God watching over me that day. Besides, it was a good Bahco wrench, made in Sweden; it has a special place in my tool box.

In all these theaters they used what was called "technical ground" for the sound equipment. It was essentially a huge ground grid buried at considerable depth into the soil, before the concrete floor of the house was poured. This ground was completely isolated from all other safety electrical grounds in the building, and was only used for the audio gear. I never looked into it, but they may have been using transformer balanced power for the audio gear as well.

For any ground to be legal, it MUST be connected to the protective ground at the service entrance. What you describe is known as an equi-potential plane or grid, and helps insure that any voltage drop due to a high current short circuit can't vary across the grid. It's used in theatre because sometimes water may be present, or bare feet, so keeping the ground at equi-potential prevents fault voltages from developing across the plane. This plane is treated as building steel and is bonded to the building's protective ground system.

There is a type of ground called a "high impedance" grounding system, used where the size of the system would generate explosively destructive fault currents. the voltage developed across the impedance is used to trip the protective device in the event of a fault without destructive currents flowing. This is generally used in very, very large industrial and sometimes commercial applications, and not for general lighting & power circuits. I have never seen it in theatres or churches, I don't ever recall seeing it in arenas either, though it's possible that it may be used to protect the feeders to the mechanical plant.

 

[byacey]

For any ground to be legal, it MUST be connected to the protective ground at the service entrance. What you describe is known as an equi-potential plane or grid, and helps insure that any voltage drop due to a high current short circuit can't vary across the grid. It's used in theatre because sometimes water may be present, or bare feet, so keeping the ground at equi-potential prevents fault voltages from developing across the plane. This plane is treated as building steel and is bonded to the building's protective ground system.

There is a type of ground called a "high impedance" grounding system, used where the size of the system would generate explosively destructive fault currents. the voltage developed across the impedance is used to trip the protective device in the event of a fault without destructive currents flowing. This is generally used in very, very large industrial and sometimes commercial applications, and not for general lighting & power circuits. I have never seen it in theatres or churches, I don't ever recall seeing it in arenas either, though it's possible that it may be used to protect the feeders to the mechanical plant.

It could well be that I'm wrong about the technical ground being isolated; but that's the way the electrical engineer that designed the ac distribution explained it to me; I may have misunderstood him.