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.