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New tale of woe...fun with Buzz at the 1984 Juno Awards

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Matthew Knischewsky:

--- Quote from: Ike Zimbel on April 18, 2024, 12:01:40 PM ---It was forty years ago today!
Sergeant Pepper told the band to... no, wait...https://www.prosoundweb.com/three-days-in-march  :P

--- End quote ---

I have had the good fortune to be in a position where I am able to turn down work at that particular venue and the surrounding property. There are some fine folks working in the local but I have heard many a tale of unnecessary struggle emanating from that part of town.

Steve-White:
Chasing hum in a situation like that, most of us would have had a similar experience and never thought to check the ground at the panel - it's assumed...   :)

Tim McCulloch:

--- Quote from: Steve-White on April 21, 2024, 09:14:51 AM ---Chasing hum in a situation like that, most of us would have had a similar experience and never thought to check the ground at the panel - it's assumed...   :)

--- End quote ---

Two stories to tell -

First at an historic vaudeville/movie house of the "atmospheric" motif, so the original electrical service has a very "Dr Frankenstein's lab" vibe, although much of it was decommissioned and replaced with modern service (red herring alert).  In the update the architect specified 208/120 100 amp service for SL and SR (no herring here), below stage level (floor pocket) in power vaults (the orchestra pit and seal room were between them).  Popular band from the 1970s, not my show, call from PA provider about hum/buzz.  "PA is quiet until we connect the monitor split; monitors are quiet until we connect the PA split.  I've used every Pin 1 lift I have, do you have 8?"  PA power is SR, monitor power is SL.

Second is personal, and how I nearly did great bodily harm to another PA provider after I recovered.  "Rock on the Tarmac" at general aviation airport, we're providing additional subs, power, and processing for the subs.  Airport electrician wires in 2 feeders to 2 circuit breakers for 120/240v 100 amp service in a brand new panel in a newly built hanger.  Most of the PA was on one distro, and our sub power and DSP was on a second distro.  Another of those "it's quiet until we put them together" problem.  Audio isolation transformers only changed the sound of the hum; pin 1 lifts were more successful.  I then ask the PA provider if the neutral and ground in each of his distros are unbonded.  "Of course!"  After the show, I do the disconnect at the panel as the electrician is at the other end of the ramp, disconnecting food vendors.  On the second service, the electrician (for reason I'll never understand) stabbed the neutral into the bus bar from the Line bus side.  When I removed it, the neutral feeder wire grazed a line bus 'finger'.  The result was a loud bang and flash (neither of which I remembered immediately after), and a coworker leaning over me asking if I was okay.  Eventually I got up, ears ringing, and followed the feeder to its distro.  I opened the distro, found the neutral and ground bonded (hence the arc flash), so I took my diagonal cutters and installed high impedance air gaps in every conductor, put the cover back on, and vowed to kill that SOB.  Revenge is a dish best served cold and Mother Nature took care of for me a few years later.

So anyone want to guess the problem in the lovey atmospheric theater?

All of this was around 25-30 years ago, and both directly changed the ways I deal with show electrical distribution, how I specify power needs, and how I work as a show electrician.

Geoff Doane:

--- Quote from: Tim McCulloch on April 21, 2024, 01:18:45 PM ---
So anyone want to guess the problem in the lovey atmospheric theater?


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It sounds like the bond screws (ground to neutral) in the disconnect switches had not been removed.  The neutral shares any current it has with the ground, thereby causing a [variable] drop on the ground reference for the two systems.  You might get away with this today, but 35 years ago the pin 1 problem was much more common, and hum was the result.

GTD

Scott Helmke:

--- Quote from: Steve-White on April 21, 2024, 09:14:51 AM ---Chasing hum in a situation like that, most of us would have had a similar experience and never thought to check the ground at the panel - it's assumed...   :)

--- End quote ---

Well, it shouldn't be assumed. If you have anybody (including yourself) tie in a distro, pull out a meter and check every connection. Make sure that everything does what you'd expect, like an actually voltage reading between hot and ground, and a very low voltage between neutral and ground.  And if no discernable voltage between neutral and ground, then make sure there's continuity between the two.

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