Lighting system causes buzz/hum in the circuit breaker panels

Mike Caldwell

Mike Caldwell

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Jan 13, 2011
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Covington, Ohio
www.mikecaldwellaudioproductions.com
I should have posted this here rather than in "Install" in the first place!

At an install where I put in the sound system their lighting system causes buzz in portions of the system when dimmed. Pin one lifts, isolation transformers do not help at all. When checking all the outlets for proper wiring I noticed a considerable amount of buzz coming from the the main breaker panel and the sub panel feeding the lighting circuits. When the lights are full up there is no buzz at the breaker panels or in the system. They have four NSI dimmer packs all on separate circuits. The building was a machine shop and has a three phase power service, not sure how the lighting circuits are divided between the phases.

Any ideas!
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

The dimmers are dumping harmonics back up the neutral line.... which makes me wonder about the electrical service in the venue. Machine shops use 3 phase DELTA, which has no neutral. I think you need to have an electrician look at how the transformer for the 3 phase WYE was installed and bonded to ground.
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Another thought, Mike... there have been some docs online about the kinds of problems that make a circuit panel *vibrate* and hum, but I can't remember where or when I read them. Perhaps a post to the Mike Holt electricians forum or a search thereof is in order.
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Mike Caldwell said:
There are actually three transformers feeding the building! Former machine shop turned into a church is the building history.

I'll suggest they get an industrial electrician to look at the power service.
Click to expand...

Ah yes.... Delta vs. Wye 3-phase wiring. There's actually very little Delta 3-phase in buildings anymore. It's now reserved for power transmission over high-tension lines. Most industrial 3-phase is WYE connected with a neutral and 480/277 volts or 208/120 volts. However, there's something really interesting and scary that happens with 3-phase Wye connections that have unbalanced current draw that includes a lot of harmonics (think lighting dimmer packs). Triplen Harmonic Currents. Look up Triplen Harmonics at Harmonics, Triplen Harmonics, Adjustable Speed Drive, Power Quality

Three phase WYE transformers don't like light dimmer packs because the odd-order harmonics from the dimmers build up on the neutral leg since the hot legs are separated by 120 degrees of phase shift. This Triplen harmonic current can sometimes be as much as 400% to 700% of the single load amperage. So if you're drawing 100 amps on a single leg of a 3-phase panel with Triac dimmers, there can be 400 to 700 amperes on the neutral bus between the transformers themselves. That's why the neutral bus in 3-phase lighting installations need to be oversized or it will burn up at relatively small dimmer pack loads. I've also got to believe that these 3rd harmonic Triplen Currents will do all sorts of mischief if connected to a sound system, which could be the source of your buzzing. Any there's probably enough harmonic currents there to actually make a panel physically buzz.

There was also a hybrid Delta/WYE transformer variation of 3-phase power from the 50's/60's called a High Leg (or Wild/Red Leg) Delta connection. See High-leg delta - Wikipedia, the free encyclopedia for an overview. This was done as a way to save transformers on industrial buildings since you can pull 120 volts from Neutral to two of the low busses, and 240-volts between the two low busses, but the 3rd High-Leg measures 208 volts from the Neutral. Be very careful around this type of panel as it's a good way to blow up 120 volt gear, especially lights.
 

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Re: Lighting system causes buzz/hum in the circuit breaker panels

For sure, at large sites with more than one power source, High Leg (or Wild/Red Leg) Delta connection's can cause all kinds of problems co-mingling Neutral and Ground currents. This is a problem that is seldom recognized or discussed.
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Kevin Graf said:
In a thread that drifted somewhat off-topic, Jim Brown posted:[ProAud] Grounding practices inside an unbalanced...and[ProAud] Grounding practices inside an unbalanced...
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Great post!!! Some of the nastiest power I've ever used was in old warehouses converted to clubs. Of course they never ran new power panels or distro since the old ones had so much amperage. Without a dual trace o'scope you can't measure the difference between two legs of 120/240 with a 180 degree phase shift (single phase) and 120 degrees phase shift on two legs of a High-Leg Delta feed, since they both measure the same with a DMM. Standard WYE connections read 208 volts leg to leg and 120 volts neutral to any hot leg so you have a hint you're on two legs of 3-phase power.
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Mike Caldwell said:
At an install where I put in the sound system their lighting system causes buzz in portions of the system when dimmed.
Click to expand...

Standard answer: Although the cause of the noise may be the lights, its not their fault; a correctly configured audio system will reject buzzes and hums from lighting and other external sources, except under a small number of specific circumstances.

Question one: Does the entire sound system operate from one socket outlet using entirely its own distribution? If you use multiple sockets to power the system (say one at stage for the amps and another in the house for the desk) then you have multiple grounds, and with that the possibility of electrical noise appearing between the grounds which may break through into audio. The problem is exacerbated in locations where there are multiple panels, and especially when they are incorrectly wired, or perhaps more honestly, wired in a way that hasn't been acceptable for many years.

Question two: Is there any electrical connection to the sound system to "something else", such as a metal DI box on a steeldeck stage with a parcan from the lighting boys also on the steeldeck? Or is the Lx desk powered off the sound power distribution?

Dimmers often do physically make a racket, and if you get enough of them they can make busbars rattle as well. In RnR you don't normally notice the dimmer racks buzzing over the noise of the PA, but in theatre, dimmers can stick out like a sore thumb.
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Just wanted to follow up on what became of this issue and the fix.
There were multiple problems contributing to noise in the system and the buzzing directly from the breaker
panels all from improper electrical wiring and the power service to the building. The building power service is delta three phase with the 208v. "wild leg"

The power company was called and sent a crew to check the delta three phase service into the building. Of the three transformers feeding the building they found one that was bad and replaced it.

The lighting circuits were all wired on to the same phase. Dividing those circuits between the two 120v phases took care of the breaker panel buzz and helped the buzz in the system.

In the sub panel feeding the lighting and sound system circuits the bonding screw for ground and neutral was in place and the buss bars had both ground and neutral lines coming from the outlets tied together. removing the bonding screw and separating the grounds and neutrals to their proper buss bars took care of the system buzz completely.
 
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Re: Lighting system causes buzz/hum in the circuit breaker panels

Mike Caldwell said:
In the sub panel feeding the lighting and sound system circuits the bonding screw for ground and neutral was in place and the buss bars had both ground and neutral lines coming from the outlets tied together. removing the bonding screw and separating the grounds and neutrals to their proper buss bars took care of the system buzz completely.
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If I had a nickel for every sub-panel Neutral/Ground bond I've found, I could buy each of you a very expensive drink. I think that's perhaps the leading cause of hums and buzzes in modern sound systems. And I've met modern-day electricians and inspectors who still do this on new installations. Got-Ta-Keep-Em-Sep-Par-Ra-Ted :D~:-D~:grin:
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Mike Sokol said:
If I had a nickel for every sub-panel Neutral/Ground bond I've found...
Click to expand...

Yeah, know what you mean.

I had a dimmer on the workbench a couple of years ago, an old specimen, but one of which there are loads of around New Zealand, they are the "standard" dimmer. Anyway, I plugged it in and the bench RCD (GFCI) tripped. Odd, I thought... So I opened her up and...

tl_dimmer_bond.jpg


When the faxed diagram arrived, the bond was shown on there too. Just to be clear - this is a dimmer with a 5 pin plug on it intended to operate off a three phase socket.

Turns out that every dimmer that left the factory for decades had this bond, and worse than that, many are still in use every day. and still have this bond.

Un-be-fookin-leave-able.
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Mike Sokol said:
If I had a nickel for every sub-panel Neutral/Ground bond I've found, I could buy each of you a very expensive drink. I think that's perhaps the leading cause of hums and buzzes in modern sound systems. And I've met modern-day electricians and inspectors who still do this on new installations. Got-Ta-Keep-Em-Sep-Par-Ra-Ted :D~:-D~:grin:
Click to expand...

It's funny how everyone talks about "bad power" and "bad grounding" when so often the real culprit is "bad neutraling" :)

Jason
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Jason Lavoie said:
It's funny how everyone talks about "bad power" and "bad grounding" when so often the real culprit is "bad neutraling" :)

Jason
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I just did a sound consult at a church over the weekend that had all sorts of system hum, and I suspect that at least some of the ground loop current is due to non-isolated ground Edison outlets in metal boxes tied to metal studs in the wall and sub-panel double G-N bonding. Lucky for them they have a licensed electrician in the church so I gave him a check list of things to look for this week. He's going through every sub-panel looking for extra neutral/ground bonds and swapped G-N wires, identify all metal outlet boxes tied to the building frame, and will be moving the metal amp rack over so a steel tension cable isn't dragging on it anymore. He's to report back to me in a few weeks with what they've found, and I'm betting he's going to discover at least a few "Bad Neutraling" things. :lol:
 
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Re: Lighting system causes buzz/hum in the circuit breaker panels

Jason Lavoie said:
It's funny how everyone talks about "bad power" and "bad grounding" when so often the real culprit is "bad neutraling"
Click to expand...

Nope, the issue is bad grounding.

If a sound system has a single consistent ground then you have a fighting chance of building a quiet system, in terms of interference. It doesn't matter what phases the system are on (myth: sound all needs to be on the same phase) or if you are on the same phase(s) as the lighting, a/c, elevators, motion control platforms or whatever (myth: sound need to be on a phase the lights don't use), you need the ground right.

Even if the building is riddled with bad bonds in all the wrong places, if you have a single ground point for sound you can still run clean. It's just much harder as, for reasons I noted above, just a DI box resting on the steel deck next to parcan can wreak havoc.

If the sound system is powered from several outlets around a facility then problems are likely. This happens universally in poorly thought through permanent installs.
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

David Buckley said:
Nope, the issue is bad grounding.

If a sound system has a single consistent ground then you have a fighting chance of building a quiet system, in terms of interference. It doesn't matter what phases the system are on (myth: sound all needs to be on the same phase) or if you are on the same phase(s) as the lighting, a/c, elevators, motion control platforms or whatever (myth: sound need to be on a phase the lights don't use), you need the ground right.

Even if the building is riddled with bad bonds in all the wrong places, if you have a single ground point for sound you can still run clean. It's just much harder as, for reasons I noted above, just a DI box resting on the steel deck next to parcan can wreak havoc.

If the sound system is powered from several outlets around a facility then problems are likely. This happens universally in poorly thought through permanent installs.
Click to expand...

Right, but the point is that it is often bad/improper neutral bonding that causes the grounding issues that force you into single point grounding.
if everything is done properly we *should* be able to plug in equipment wherever we want.

and I agree about the phases. so many people have told me that and I ask them how much of their hardware converts the AC to DC? and the answer is all of them.. and then the question is, well, once it is converted to DC how does the timing of the AC make any difference?

Jason
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

Jason Lavoie said:
Right, but the point is that it is often bad/improper neutral bonding that causes the grounding issues that force you into single point grounding.
if everything is done properly we *should* be able to plug in equipment wherever we want.

and I agree about the phases. so many people have told me that and I ask them how much of their hardware converts the AC to DC? and the answer is all of them.. and then the question is, well, once it is converted to DC how does the timing of the AC make any difference?

Jason
Click to expand...

Exactly right.... and using different phases generally has nothing to do with hum or buzz. That's an old-wives tale....

In my experience, neutrals with noise often contaminate the safety ground bus with all sorts of induced voltages. But remember that even a "clean" neutral that's been accidentally double bonded at a sub panel will induce 60-Hz ground loop hum (without harmonic content). That's because there's always some kind of voltage drop in a neutral (or any wire) carrying current. All you have to do is poke your DMM between the neutral and ground pin of a properly grounded outlet and you'll generally find a volt or two difference if there's anything turned on in the building. If you don't see that normal voltage difference, then some ill-informed electrician has bonded the neutral and ground bus'es together in a sub panel trying to make a "better" ground. That's a violation of the NEC, but happens all the time to me, even in new buildings.

That's what seems to induce 60-Hz ground loop current "hum", while higher frequencies on the neutral from triac dimmer spikes or Triplen currents from 3-phase Delta wiring seem to cause the "buzz".

Yikes....

I still contend that you can figure out the best place to begin troubleshooting audio system noise by just listening to the frequency and harmonic content of that noise. Of course it helps if you're a musician (I'm one of 56+ years), but a simple RTA FFT program will show you what your sound system "noise" is composed of. Not a 100% obvious identifier, but certainly a start. Also, a clamp-on ammeter around the exterior of an XLR mic cable with show 60 Hz "ground loop" currents rather easily since they're on the order of 1 amp per 1 volt of ground differential.

I've done a lot of experimenting with this on the bench, and have included a picture of the portable demonstration kit from my No~Shock~Zone and ASSIST installer seminars. Note the little red "Glo-Melt" resistance soldering transformer in the middle which I've wired to inject up to 3 volts and 30 amps of ground-loop hum between any two pieces of audio gear. In class we use a bunch of different brands of amplifiers and active speakers to listen for the "pin 1 problem" as it's often called.

Good times.... :lol:

Mike Sokol
 

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Re: Lighting system causes buzz/hum in the circuit breaker panels

Using one's ears is very good advice.

If one stands next to a transformer, if one hears the deep hummmmmm of the fundamental, then that is lovely. If one hears the buzzzzzzzz of the third harmonic, one knows there are triplens present, and one ought to expect big neutral currents. And heat. And trouble generally.
 
Re: Lighting system causes buzz/hum in the circuit breaker panels

David Buckley said:
Yeah, know what you mean.

I had a dimmer on the workbench a couple of years ago, an old specimen, but one of which there are loads of around New Zealand, they are the "standard" dimmer. Anyway, I plugged it in and the bench RCD (GFCI) tripped. Odd, I thought... So I opened her up and...

tl_dimmer_bond.jpg


When the faxed diagram arrived, the bond was shown on there too. Just to be clear - this is a dimmer with a 5 pin plug on it intended to operate off a three phase socket.

Turns out that every dimmer that left the factory for decades had this bond, and worse than that, many are still in use every day. and still have this bond.

Un-be-fookin-leave-able.
Click to expand...



I know exactly which dimmer this is. I discovered the same thing when it was attached to a RCD protected distro outlet, thing kept firing for no reason. Till I opened dimmer and removed that link. There must be hundreds of them still around like that. We have a couple of the newer rack ones, and they're ok. :)~:)~:smile:
 
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