Bad dimmer noise (interference?)

JD, and everyone else, you'll probably jump all over me for this, and deservedly so, but I once eliminated a great deal of 60Hz buss in a road audio system by tieing the ground and neutral together at the main audio distro, by using a MM cam and a 10' 4/0 cable into the CamLok pass-thru outputs. The House Electrician would not do it at the beginning of the feeder, but said he had no problem if we did it at the end of the feeder. Again I AM NOT advocating this. I'm interested in hearing what those with many years of experience think.

Previous to this, I was once told, by a University's Buildings and Grounds Electrician, to tie the neutral and ground together at the lugs of a portable dimmer pack, as he had only run 4 wires (no neutral) and I had five lugs. His exact words "Tie the neutral and ground together, the potential difference is zero." Again I AM NOT advocating this. I'm interested in hearing what "experts" think.
 
Thank you for the lesson. I did not completely understand everything, which just reinforces the point that I really need to learn electrics to be responsible doing sound on my own (like for small afairs that only need one techician).

Because when everything works it is great, but if something goes wrong it can go very wrong.
 
you'll probably jump all over me for this, and deservedly so, but I once eliminated a great deal of 60Hz buss in a road audio system by tieing the ground and neutral together at the main audio distro, by using a MM cam and a 10' 4/0 cable into the CamLok pass-thru outputs.

Ground loops can be really tricky. When balancing safety issues, one most also take into account the effect of six to ten thousand rioting fans bludgeoning you to death because the show is not starting! Within reason, you do whatever you have to, to get the show to go on, so no flaming from me. Many times, ground loops and induction/transmission can be fixed in several ways, depending how much time you have. In this case, bonding at the sound distro probably diverted the inducing current away from the route that was causing the problem. Somewhere, something else was wrong, but it is so common in a live show to have 50+ channels of mix, and the nasty thing is loops don't always make the noise on the channel that is causing them! So, you could either spend the next 15 hours getting to the root cause, or work around the problem.

The kicker is that sometimes the buildings themselves are the problem!
I did a show in a place called AG Hall in Allentown PA, and we had a horrible buzz! We ended up bonding our G/N at our main distro and the problems was gone. I had about an hour before the show, so I spent some time looking at the building structure. What I found was that the cable at their transformer pad (other side of wall) was snapped off the grounding stake! In effect, there was no main ground and the system was finding its neutral-ground bonding in building wiring boxes that were attached to the steel frame of the building! The problem here is that often the electric company ties it's low line on the 13.5k feed to the secondary neutral, which can bring in all sorts of problems from the outside world!

The following is NOT recommended for anyone, no way, no shape, no how!: Being the nice dumb guy I was back in the 80's, I climbed into the cage and reconnected their ground. We then pulled our "bond" off at the distro, and sure enough, the problem was gone.

Although ground loop and buzz problems always have a simple cause, often finding them makes you feel like you should be calling in a psychic! To make matters worse, nothing gets tempers flaring between road crew, house crew, promoter, band/act, and lighting & sound contractors like a good unresolved buzz hours (or minutes) before Showtime!

Clarification: Forgot to mention that sound and stage were getting their power off of our distro, thus the problem and extra tension! Also, the distro bond did not get rid of all the noise. Reconnecting the ground stake did.
 
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Just want to throw out the fact that if something like this "just happens overnight", try to find out what the cause is. If the cleaning crew tripped over a wire and plugged it back into the wrong outlet, that is one thing. If something has happened to your feeder cable, distro, etc. This little clue can help prevent other serious issues / injuries if there is something damaged in the high current end.

On the com side, I have found that the RTS wireless packs will introduce a nasty hum into the intercom channel. I won't say how "I" fix it but you can imagine.

kw
 

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