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Author Topic: Dangerous AC situation in reception hall - PLEASE READ  (Read 122751 times)

Mike Sokol

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Re: freak accident? help!
« Reply #50 on: May 07, 2012, 01:34:21 pm »

I just did a consulting gig at a medium sized church in New Jersey, and EVERY outlet I looked at was bootleg grounded, but none that I tested was reversed polarity. Of course, bootleg grounded outlets by themselves are not dangerous to humans or sound gear, but there was ground loop hum galore that was modulated by the current draw of the amps. The sound techs in the church had attended one of my training classes last year, so they knew better than to cut off ground pins on the extension cords. And they had put in a few HumX ground lifts which cut the hum considerably, but I don't think there was a single properly grounded outlet in the entire place. Yikes!!!!!

Mike
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Paul Dershem

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Re: freak accident? help!
« Reply #51 on: May 07, 2012, 03:49:32 pm »

Thanks for the info, Mike.

After reading your posts, I started researching non-contact units like the one you recommend. One article said some are powered by small disk batteries (like watch or hearing aid batteries), while others are powered by AAA cells, which can be purchased just about anywhere. Pragmatism draws me to AAA batteries.

Sadly, it's hard to determine from websites like Amazon what kind of batteries a specific unit takes. Can you shed any light on this? How often do yo have to replace batteries on units that are always on vs. units that have to be switched on?
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Samuel Rees

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freak accident? help!
« Reply #52 on: May 07, 2012, 04:28:33 pm »

This has been a great thread. I learned a good bit about a serious safety issue that I was apparently ignorant of previously, and I'm going to pick up the recommended gear to test with ASAP.

OP - Thanks for the post, glad no one was hurt.
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Chris Hindle

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Re: freak accident? help!
« Reply #53 on: May 07, 2012, 04:47:39 pm »


Sadly, it's hard to determine from websites like Amazon what kind of batteries a specific unit takes. Can you shed any light on this? How often do yo have to replace batteries on units that are always on vs. units that have to be switched on?
I have had the Fluke <no tone> model for 10 or 12 years now. It is always on, and the AA (or AAA - I forget) lasts me 4 or 5 years. I probably use it at least a dozen times each show, and whenever I am screwing with the house or office electrical.
A little tap on the sensor prong makes it blink - easy test before each use
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Mike Sokol

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Re: freak accident? help!
« Reply #54 on: May 07, 2012, 04:56:57 pm »

I have had the Fluke <no tone> model for 10 or 12 years now. It is always on, and the AA (or AAA - I forget) lasts me 4 or 5 years. I probably use it at least a dozen times each show, and whenever I am screwing with the house or office electrical.
A little tap on the sensor prong makes it blink - easy test before each use
The Fluke VoltAlert takes AAA batteries which, of course, are available anywhere. I think that most any brand non-contact tester made by Amprobe, Sperry, Triplett, and others... would work for detecting a RPBG. You DO NOT want a low-voltage non-contact tester (24 volts), get one listed for 80  or 90 volts to 600 or 1,000 volts.. A low voltage tester will blink and beep anywhere NEAR a powered outlet, when you want a tester that will allow you to differentiate between the hot and neutral contacts in a wall outlet.

Mike

 
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Paul Dershem

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Re: freak accident? help!
« Reply #55 on: May 07, 2012, 05:46:23 pm »

Thank you, gentlemen.
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Mike Sokol

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Re: freak accident? help!
« Reply #56 on: May 07, 2012, 06:18:15 pm »

Thank you, gentlemen.
I'm glad this info is helpful... but realize that most of the pro-audio and electrical test gear manufacturers aren't aware of how dangerous RPBG outlets can be, or that their own test gear won't identify the condition. 

So to promote this issue to the various manufacturers and agencies I need pictures of any examples you've come across. If you have pictures of any burned up audio gear or hot electrical outlet grounds, please post them here or email them to me directly at mike@fitsandstarts.com   

Thanks.... Mike
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John Roberts {JR}

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Re: freak accident? help!
« Reply #57 on: May 07, 2012, 07:02:46 pm »

I'm glad this info is helpful... but realize that most of the pro-audio and electrical test gear manufacturers aren't aware of how dangerous RPBG outlets can be, or that their own test gear won't identify the condition. 

So to promote this issue to the various manufacturers and agencies I need pictures of any examples you've come across. If you have pictures of any burned up audio gear or hot electrical outlet grounds, please post them here or email them to me directly at mike@fitsandstarts.com   

Thanks.... Mike

I wouldn't say this problem is exactly unknown to manufacturers and safety agencies...

As i posted UL has a ground bonding test that confirms properly designed "safety" grounds will not vaporize or allow dangerous voltage rise while passing several tens of amps, long enough to trip the primary breaker.

There is a gray area perhaps regarding non-"safety" grounds, like your sundry examples that inadvertently got in the primary current path and did not hold the current as is UL's plan for safe shutdown of the fault.  IIRC there is some fine print in the UL regulations that qualify bonding only for external connections labelled as "Ground".  As i recall my in house guy told me I could relabel my barrier strip ground screw as 0V instead of ground and wouldn't need to pass the ground bond test, but i redesigned the board to pass because it was the right thing to do (damn I can't imagine not doing that). 

I am not suggesting that all these companies are skirting the safety regulations, because XLR pin 1 is not formerly labelled as a "safety ground", and many legacy designs (and probably some current ones) wouldn't pass the safety bond test. Maybe pin 1 should be formally labelled "ground" and safety tested... ? 

For awareness, how about being sued, when a customer got killed between one rouge power outlet and one correct one, while using two very UL ground correct guitar amps. UL is aware of this also since they were right there in court too.

I agree this is poorly understood by many and you need to keep raising a stink... but this isn't exactly a secret...

JR
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Mike Sokol

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Re: freak accident? help!
« Reply #58 on: May 07, 2012, 07:28:00 pm »


I agree this is poorly understood by many and you need to keep raising a stink... but this isn't exactly a secret...

JR
I agree it's not exactly a secret. But testing for raised potential on grounds isn't known by most electricians and inspectors. The standard check by inspectors is still the 3-light testers, and as you can see from the beginning of this thread most everybody will assume that a 3-light tester or metering between H-N-G will guarantee a safe electrical outlet, when in fact it will miss this dangerous condition. I've also raised the idea of hot grounds with the RVIA and RVDA (Recreational Vehicle manufacturers associations) and they didn't want to promote hot-skin testing of RVs since it would "scare" consumers into not purchasing an RV or trailer.  Perhaps there's a little of this with audio manufacturers as well, since their own equipment is not at fault, but plugging into a mis-wired outlet can certainly wreak havoc.

Another really interesting tangent to the idea of RPBG is that lightning strikes on buildings can burn out the exterior grounding rod. In one case the ground rod fused the sandy soil into a ground rod Popsicle made of glass, essentially insulating it from the earth. I found this out when the facility noted that the lighting board operator could feel tingles in his fingertips that matched the lightning flashes outside. The ground-neutral bond in the main panel was floating above the earth by 40 volts or so, but when a lightning cloud went overhead it would pulse to a few hundred volts. The entire building's electrical system had lost its ground reference, which of course is what the ground rod is supposed to supply in the first place. From my conversations with several power station operators, there is no code requirement for a building ground to be retested after a lightning strike. So the first strike can take out the ground rod connection, leaving everything inside the building susceptible to side flashes from the next near lightning strike.

The point is that while the majority of building electrical systems are safe, there are a few of them with incorrect wiring that never seems to get fixed. That's largely due to the fact that when a piece of gear blows up, very few people perform a system test to REALLY see what happened. They mostly assume they did something themselves to get shocked or blow up gear. And that's often not the case.

Mike
« Last Edit: May 07, 2012, 08:04:04 pm by Mike Sokol »
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Kellen Tyburski

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Re: freak accident? help!
« Reply #59 on: May 07, 2012, 08:08:58 pm »


Just to confirm, you are talking about the $25 gadget shaped like a pen? At that price, why wouldn't everyone carry one? I will be adding it to the tool box this weekend.

I have one of these (and the GFCI tester too) and I will def be carrying them with me on gigs from now on. Just so I am clear, I can quickly test for the RPBG outlet by just putting the tip of my Fluke Voltalert into the ground socket to test if its electrified?

This is a very cool thread, I will definitely be reading and re-reading it and I'm sure it will be the basis for further research...
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