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Author Topic: Dangerous AC situation in reception hall - PLEASE READ  (Read 87208 times)

Mike Sokol

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Re: freak accident? help!
« Reply #210 on: November 19, 2016, 08:13:15 am »

Thanks Mike!  That looks...well, ideal for my needs.  Not to disparage my new home town, but so far I'm batting less than .500 when it comes to finding a good, working plugin at gigs.  (Both power and Ethernet!)  $300 is cheap insurance if it saves my ENG camera and laptop from flaky power connections.  At home I have a hodgepodge of mixed aluminum and copper wiring that I suspect has not been given due care over the years.  (I found 25VAC G-N on one circuit that was supposed to be dead when I checked before removing 3 taped-together switches.)  Either way I think I'll get my money's worth in peace of mind.

I'm sure that 99% (or more) of outlets in modern homes or performance venues are properly wired. But it's that possible 1% that can bite you in the butt. A lot of that is due to the fact that we interconnect a lot of sensitive electronic gear that's often powered by multiple outlets of unknown pedigree. For instance, if you plug a toaster or slow coodker nto an ungrounded outlet or even an RPBG in your kitchen, you'll never know it. And many modern power supplies are auto-switching which means they don't care if they're plugged into 90 or 250 volts. And even a grounded appliance such as an air conditioner in the bedroom can be plugged into an RPBG outlet for decades and you might not know it for decades because you won't get shocked while standing on a wood floor. But plug your computer printer into that outlet and plug your computer power supply into another outlet and the USB cable will melt down as your computer fries.

I generally put my Suretest Analyzer on the outlet and look for obvious miswiring, then do a quickie test with a NCVT to check for an RPBG. Remember that while a Suretest or Amprobe INSP-3 will find a bootleg ground created by a G-N bond in the receptacle itself, they won't detect one at least 15 feet upstream. And they won't notify you of a hot ground created by any RPBG. See https://www.youtube.com/watch?v=_04HmpFBxdQ

Kevin Graf

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Re: Dangerous AC situation in reception hall - PLEASE READ
« Reply #211 on: November 19, 2016, 08:57:42 am »

I don't think it's 99 %. This Audio Precision note is from 3 years ago:

New Facility
Audio.TST June 2013       
Notes from the Test Bench
By Bruce Hofer, Chairman & Co-Founder, Audio Precision

Recently, AP celebrated the 15th anniversary of our custom designed building. Photo albums were displayed showing the construction and the move into our facility back in 1998. (My, how some people have changed in appearance!) Among my many memories of that time, I was reminded of a particularly nasty problem we experienced as we restarted operations in our new production environment.
Almost immediately after moving we began to experience failures of certain bench tests that are performed by our technicians during the course of product assembly and adjustment. After some research, we discovered our new building had some extremely large magnetic fields in the production area, almost as if it was haunted. These fields coupled high levels of hum into our products that were causing the test failures. AP products are designed to reject reasonable levels of stray magnetic fields that would typically be encountered in a lab or production environment. However the magnitude of the fields we faced were at least 20 dB worse.
We ultimately discovered that several of our AC outlets had been wired incorrectly, having their neutral and ground connections swapped. This is a big no-no from the safety viewpoint, but it also caused all of the neutral currents in a particular circuit (outside of our production area) to return through the safety ground connection and ultimately through plumbing and drainage pipes. Some of these plumbing pipes were located in the space directly above our production area while the main drainage pipe was buried directly below; thus our production area was effectively inside of a huge coil. Our electrical contractor was embarrassed but confirmed our diagnosis, and the problem was quickly fixed.
Sometimes one has to think “outside of the box” to correctly perceive or understand a given problem. In this case, our new building plans provided the necessary insight to recognize the inadvertent source of our unwanted magnetic fields (plumbing that formed a coil around our production area). Perhaps you might want to check the neutral and safety ground connections of the AC outlets in your own work space—there could be some ghosts present!

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Stephen Swaffer

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Re: Dangerous AC situation in reception hall - PLEASE READ
« Reply #212 on: November 19, 2016, 10:17:31 am »

I don't think it's 99 %. This Audio Precision note is from 3 years ago:


I would agree-I was in a code update class yesterday-one student that, from overheard conversations, is in at least his second 3 year license cyle meaning he has been a licensed electrician for over 6 years + the time to get his license asked a question about grounding signs-using a "concrete encased electrode."  The instructor was talking about equipment grounding conductors-an intentional metalic path back to the service by definition-he seemed perplexed by the concept that an EGC needed to me metallic.

Another interesting historical fact that was mentioned was that when dimmer's first came out they included a "ground" wire-but that ground was actually used as a neutral for the function of the dimmer-this allowed them to be used in the place of switches that had no neutral installed in the box.  Code was changed a few cycles ago to require neutrals at switch locations to allow for this.  Still, especially with audio and sensitivity to ground loops and objectionable current on grounds, this could be a problem in some buildings.

I suspect that in Mike's area-and in most large cities-licensing and inspection has been required for a few decades.  Most of Iowa had no licensing or inspection requirement until 2007-and there are electrician's that were grandfathered in that shouldn't be wiring buildings. 

Since most inspectors in this area do a 100% test of receptacles with at least a generic 3 lamp tester, I might allow that 99% correct in any new construction that has actually been permitted and inspected :)
« Last Edit: November 19, 2016, 01:32:36 pm by Stephen Swaffer »
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Steve Swaffer

Mike Sokol

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Re: freak accident? help!
« Reply #213 on: November 19, 2016, 10:40:02 am »

I'm sure that 99% (or more) of outlets in modern homes or performance venues are properly wired. But it's that possible 1% that can bite you in the butt.

Note that I said perhaps 99% of "modern homes or venues" are properly wired. If you factor in all the old wiring that's been grandfathered in, then that number has to plummet. But to your point about swapped G-N wires on receptacles, I too have found these in a number of performance venues where there was all sorts of ground-loop hum that couldn't be explained. A few of these have been big conference halls with hundreds of vendor spots, and I was only measuring where I was plugging in my own gear. So how widespread are these mis-wiring conditions? I just don't know. But I do find at least several obvious mis-wired outlets every year, and I'm just casually inspecting outlets that I'm going to plug into myself. That is, I'm not doing a formal assay of a bunch of facilities. That being said, I was recently brought in to consult on a rewiring job at a church to assure there's no ground-loop hum on their youth stage. And a big performance theater in the area has asked me to figure out why some of their outlets meter at 130 volts before they install a bunch of new LED lighting gear and controllers. According to the theater tech, they've blown up a lot of control electronics, and have decided to look at what caused the failures before they hook up their new expensive gear. 

Bill Koonce

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Re: freak accident? help!
« Reply #214 on: November 19, 2016, 12:26:54 pm »

I'm sure that 99% (or more) of outlets in modern homes or performance venues are properly wired. But it's that possible 1% that can bite you in the butt. A lot of that is due to the fact that we interconnect a lot of sensitive electronic gear that's often powered by multiple outlets of unknown pedigree. For instance, if you plug a toaster or slow coodker nto an ungrounded outlet or even an RPBG in your kitchen, you'll never know it. And many modern power supplies are auto-switching which means they don't care if they're plugged into 90 or 250 volts. And even a grounded appliance such as an air conditioner in the bedroom can be plugged into an RPBG outlet for decades and you might not know it for decades because you won't get shocked while standing on a wood floor. But plug your computer printer into that outlet and plug your computer power supply into another outlet and the USB cable will melt down as your computer fries.

I generally put my Suretest Analyzer on the outlet and look for obvious miswiring, then do a quickie test with a NCVT to check for an RPBG. Remember that while a Suretest or Amprobe INSP-3 will find a bootleg ground created by a G-N bond in the receptacle itself, they won't detect one at least 15 feet upstream. And they won't notify you of a hot ground created by any RPBG. See https://www.youtube.com/watch?v=_04HmpFBxdQ
In my case, I have two potential problems to contend with.  The first is widespread deployment of aluminum wiring here since 1960, before compatible terminal gear was available.  (In Chicago, the Sears Tower had to have all switches and outlets replaced after it was discovered that they were only Cu rated when installed c. 1970 with all Al wiring.)  In my own home, I have a couple of later additions that muddy the waters even more--the additions used copper wire since that was cost effective at that time.  And I think that a lot of the home wiring was done by the owner, who was a police officer, not an electrician.  I'm pretty sure that a few of my problems are coming from less than optimal Al-Cu splices, and tired outlets.  IME when I find a flaky outlet, just cutting off the old oxidized wire, exposing shiny wire and attaching that to a shiny new socket will make it rock solid.  That's the time to fix any wrong wiring too.

At work there's the possibility of flaky Al-Cu joins, plus wall outlets that have been treated roughly by cleaning crews who think nothing of unplugging a vacuum cleaner by tugging on its power cord until something gives.  Up north a conference room will often have a "conditioned" outlet behind a panel that is verboten for the cleaning crew to use, along other structured wiring hookups just for AV use.  Although I'm just starting to explore the various venues of Albuquerque, the ones that I've worked in to date don't have modern structured wiring, and wall outlets that have taken a beating over years.  Like the old XLR jack for the PA that has had the push-to-disconnect tab mangled.

I'm a subcontractor for this gig, and would love to be able to grow my role by being the AV/PA provider too (I already lug a lot of stuff to each gig as backup in case the hotel system fails), but so far my client's client isn't interested.  C'est la vie.
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