Lighting system causes buzz/hum in the circuit breaker panels

[Mike Caldwell]

While were still talking grounding

I'm working with a new install, new building, very simple sound system. The system was speced and designed by an out side engineering company. It calls for a ground buss in the equipment rack with each piece of audio equipment tied to it with a jumper connected at some point on the audio equipment's chassis. The bar itself is connected to a ground reference point in the tel com / data room with a run of number 6 wire, in this case that will be about a 200 foot run.

While I've seen this done in large phone switching systems, server rooms and radio transmitter sites I think it's a little over kill in this system.

Any possible issues with the equipment chassis having two completely different ground paths, one with the AC power and the other via the buss bars back to the tel com / data room.

 

[Mike Sokol]

Re: While were still talking grounding

I'm working with a new install, new building, very simple sound system. The system was speced and designed by an out side engineering company. It calls for a ground buss in the equipment rack with each piece of audio equipment tied to it with a jumper connected at some point on the audio equipment's chassis. The bar itself is connected to a ground reference point in the tel com / data room with a run of number 6 wire, in this case that will be about a 200 foot run.

While I've seen this done in large phone switching systems, server rooms and radio transmitter sites I think it's a little over kill in this system.

Any possible issues with the equipment chassis having two completely different ground paths, one with the AC power and the other via the buss bars back to the tel com / data room.

I'm heading out to teach a class right now on "hums and buzzes", so I don't have time to offer you ideas until later tonight. But at first blush this does appear to be overkill for your situation. I've mostly seen this sort of bus-bar arrangement at studios built right next to radio transmitter sites, where the RF is so strong that just holding VU meter in your bare hands will move the needle. If you can send any more details about the installation on this thread today, I'll take a look at it tonight and see if I can offer any suggestions.

 

[David Buckley]

Re: While were still talking grounding

Any possible issues with the equipment chassis having two completely different ground paths, one with the AC power and the other via the buss bars back to the tel com / data room.

I was musing over whether there are two ground paths or just one ground network...

But then it occurred that I really should be wondering about is what your telecom and other equipment connected to the technical earth is going to think of being connected to a power system earth over 200 feet away. Are the telecom and data guys OK with this...? If their tech earth is clean now, then it probably wont be after suffering this imposition.

 

[Mike Caldwell]

Re: While were still talking grounding

This is what is and should have stayed a simple system. It's eight ceiling speakers in a cafeteria, Shure rack mount strip mixer, CD player, couple of wireless mics, a few mic jacks around the room and a Crown CTs power amp. Now here are a few more over kill items speced in the system, a little processing is always needed but a Bi-Amp Nexia probably not. For nothing more than some bouncing LEDs lets add an Atlas Sound monitor panel. Atlas Sound - MVXA-2016 . Called for it to be paralleled to each input, to bad it only takes line or speaker level inputs!

Ok I'm starting to rant about design "engineers" who don't get out in the light of day too often and use the copy and paste function way too much when designing systems. Don't even get me stated on specs that until a couple years ago were still going out to bid with cassette tape recorders for music rehearsal rooms!

Let get back to grounding buss bars, at this time not sure where telecom is getting their ground reference from in their racks.

 

[Mike Sokol]

Re: While were still talking grounding

This is what is and should have stayed a simple system. It's eight ceiling speakers in a cafeteria, Shure rack mount strip mixer, CD player, couple of wireless mics, a few mic jacks around the room and a Crown CTs power amp. Now here are a few more over kill items speced in the system, a little processing is always needed but a Bi-Amp Nexia probably not. For nothing more than some bouncing LEDs lets add an Atlas Sound monitor panel. Atlas Sound - MVXA-2016 . Called for it to be paralleled to each input, to bad it only takes line or speaker level inputs!

Ok I'm starting to rant about design "engineers" who don't get out in the light of day too often and use the copy and paste function way too much when designing there systems. Don't even get me stated on specs that until a couple years ago were still going out to bid with cassette tape recorders for music rehearsal rooms!

Let get back to grounding buss bars, at this time not sure where telecom is getting their ground reference from in their racks.

If the entire sound system can be powered from a single 20-amp power outlet, and you keep its ground separate from building steel, there's really no need for all the copper bus bars. As mentioned earlier the simplest single point grounded sound system should be pretty much immune to any ground noise. Sounds like somebody is trying to sell you a lot of copper.

I do know that according to the NEC you can't disconnect your outlet grounds by breaking off the sound gear's ground pins and bond it to this external bus bar. And if you mount your gear directly in the rack without isolation washers you'll create yet another potential ground loop path. The big ground bus bar solution is typically a brute force method used in radio stations and such as you originally mentioned. And certainly it's possible for your sound system (if accidentally bonded to the neutral bus or building frame somehow) could contaminate the telcom technical ground system.

I think this all sounds like a bad idea. A standard isolated ground power system and properly connected sound components shouldn't hum at all. Are they more worried about hum, or buz, or RF/Digital interference from the Telcom system? Anything else you can provide?

 

[Mike Caldwell]

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

Yes the system will be powered of a dedicated single 20 amp circuit.

Not really sure what the designer would be worried about, most likely this is a copy and paste item left over from a design that MAYBE actually called for such grounding extremes.

 

[Joel Lefort]

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

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...

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.

Pardon, but I'm having a difficult time seeing exactly what is wrong with this. You mention the ''bond'' but I'm not entirely sure what two items are bonded together.

 

[Tim McCulloch]

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

Pardon, but I'm having a difficult time seeing exactly what is wrong with this. You mention the ''bond'' but I'm not entirely sure what two items are bonded together.

The ground bus and neutral bus are "bonded" (jumped) together inside the device, which violates best practices and most electrical codes.

 

[Joel Lefort]

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

The ground bus and neutral bus are "bonded" (jumped) together inside the device, which violates best practices and most electrical codes.

edit: Sorry, I see the brass jumper now between the neutral and ground bus. wow...

 

[Mike Sokol]

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

The ground bus and neutral bus are "bonded" (jumped) together inside the device, which violates best practices and most electrical codes.

Yup.... and this is exactly the sort of thing that creates safety ground differential voltages in building power, which can result in ground loop currents that cause hum and buzz in audio systems. Perhaps it's also one of the reasons that lighting dimmer systems get such a bad rap from audio techs.

 

[Jordan Lahr]

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

Its also the noise the sinewaved power produces if your audio cables aren't shielded properly when run next to dimmed power.

 

[Mike Sokol]

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

Its also the noise the sinewaved power produces if your audio cables aren't shielded properly when run next to dimmed power.

I used to think it was all about the shielding... but then I got to use some InstaSnakes which are basically XLR to RJ-45 converter boxes that use UTP (Unshielded Twisted Pair) CAT5 wiring to run mic-level signal.

See Energy Transformation Systems ETS InstaSnake PA202 Series 4-Channel Phantom Power Compatible CAT5 XLR Audio Baluns Audio Over CAT5 Systems at Markertek.com

Believe it or not, but I've run InstaSnakes with mic level signals over several hundred feet right along side a bunch of power cables. It's all about the CMRR of the balanced input stage, and an audio transformer typically has a GREAT Common Mode Rejection Ratio. That's why the phone company could run unshielded twisted pair for thousands of miles across the country with reasonable fidelity and S/N ratio.

Interesting, isn't it?

 

[Jordan Lahr]

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

They key with that is the Twisted pair, Also was it dimmed power or clean power?

 

[Mike Sokol]

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

They key with that is the Twisted pair, Also was it dimmed power or clean power?

This was with clean power, but an awful lot of it. Plus it was all genny created power. It would be a very interesting experiment to hook up a pair of InstaSnakes using a few hundred feet of CAT5 right beside a dimmer feed for some big tungsten lighting and let the Triacs have their way with the sine waves.

I really couldn't believe how well these InstaSnakes worked in practice over UTP CAT5, and with mic-level signal to boot. I personally would never have tried it that way, and would have guessed that live-level could work but never mic-level. I don't have any of the InstaSnakes myself as I was just doing the tech setup and operation for a big political event, but I'll probably be using them again for the inauguration in DC next month. I'll do a bit more research and possibly start a new thread once I get the play with them again.