http://aolsvc.news.aol.com/news/article.adp?id=20051030192209990001

Very strange.. I wonder what was hot?
Normally the microphone would be grounded.

Microphone may have a grounded shell and shielding, but is still connected to an amplifier of some sort.

That's really sad. While in retrospect, it's really, really stupid to grab an electrical appliance like a microphone while standing waist-deep in water, I can see how it might not register on the mind that a microphone is an "electrical appliance."

The scary part is that I can imagine myself doing the same thing, without even thinking about it.

I KNOW THATS SAD.

There is quite a lot of older P.A. system gear in operation all over the country (and world.) Most of it had a capacitor/resistor combination tying one side of the A.C. line to the chassis for noise suppression.

Bear in mind that most such gear did not have a polarized plug, indeed most came with instructions to the effect of "in the event of excessive hum/noise, reverse the AC plug..."

It would not take much leakage or breakdown of that cap/resis combo to cause a strong or fatal shock. Even if the combo was on the neutral side of the line, there would still be potential for enough leakage to cause this.

A lot of houses of worship now seem to go with wireless microphones for baptisimal pools and other portions of services where there is contact with parishioners.

techie wrote:


Depends. Older gear, "grounded" to chassis, yeah. But not in the proper sense of the word grounded. Some modern gear uses isolated, electronically balanced inputs. So the shield of the cable (and body of the mike) may or may not be grounded. Take some voltage measurements from mike to a known ground on your next gig and you may be surprised.
I've been bit a few times by "hot mikes."

... I once got a nice jolt from my guitar amp,a vintage, 2-pronged plug, tube style Ampeg,and the microphone,which was plugged into a different amp(also a 2-pronged plug),and the polarity was reversed... the case,carried current and when my lips touched it....yyyouch!! the circuit was complete,..from the guitar strings,thru my body to the microphone.. Stung like a witch,..
Russ

I was onstage doing a comedy routine many years ago, when the 'MC' got electrocuted by a hot microphone. He took off like a Whirling Dervish. That was very, very frightening. He was saved by our quick-thinking Sparks, who happened to be right by the switchgear and shut the power off immediately. No harm, apart from a bruised face where he punched himself hard in the chops, and shock. One sugar cube and off to the hospital, but all ended ok.

Alan

That story is tragic.


I once got a very good jolt when my lips touched a microphone and my hands were on the guitar,

I screamed a dirty word. Unfortunately it boomed out over the PA system, right into the middle of the Church Fair that we were supposed to entertain.
My stepdad taught me about polarity while I was (not electrically) grounded.

For those looking for an easy laugh:

First, find an overly pious preacher.

Ask him if he really believes. He will, of course, answer 'yes.'

Then ask him if his church has a lightning rod on the steeple. Watch him turn purple, as he realises the trap he's fallen into.

Never been to a hospital on acid

mxslick wrote:
Take some voltage measurements from mike to a known ground on your next gig and you may be surprised.

Just the other day I had the exact same complaint from a customer of a new home I wired. They have a band and practise in the house, and apparently they are getting shocks when their lips touch the mics....would a GFCI prevent this???

Off the topic here....they are also having a hum from the bass. We have electronic dimmers throughout the house, and the homeowner has also installed quite a few compact fluorescents. Would this cause the hum?

Not likely that a GFCI would see that current unless is it comming directly from the building power supply. It is most likely from the load side of a transformer or power supply in the equipment and the line side GFCI will not "see" that leakage current.
Don

Those leakage currents can still be a problem in modern gear.

Just a few days ago I was working on a home video system and got bit as I pulled out a metal-bodied coax plug while leaning on the case with my other arm. It wasn't exactly a powerful shock, but it was certainly more than a mere tingle -- enough to make me jump.

That was the combined leakage currents from two TVs, two VCRs, a DVD recorder, and a digital receiver.

And the simple improper use of an expension cord that powers the amplifier. Was there an adapter used to defeat the EGC and a simple 2w extension cord the possibly reversing the line and neutral conductor, a defect in the EGC, broken ground EGC ground plug? All thinks that are either overlooked or disregarded by people who don't have a clue or know the importance of proper grounding. Never the less, even if all of the safety precautions were met and a GFCI outlet was used it would be in your wildest dreams that I would ever allow a wired mic be used in such a manor.
At least purchase an inexpensive cordless mic.

A somewhat off-topic remark.

If your lips are touching the microphone head, you're not using proper miking techniques.

Ideally, your mouth should be at about a fist-length away from the mic's head.

I wonder if some of these cases might be caused by the "phantom power" supply required for electret mics. Consider the tingle you get when touching your tongue to a 9 volt battery. Aren't most pop screens metallic?

To check it out, I would use my Fluke on AC & DC between the contact points(body of mic/pop screen, both to flooring matl) If I saw any substantial potential, I would probably put 100kohms in parallel with my Fluke to get a handle on the source impedance. I wonder how many amps out there have their chassis ground referenced to the negative side of a bridge rectifier???

I wonder if some of these cases might be caused by the "phantom power" supply required for electret mics.

I was wondering when someone was going to bring that nonesense up. Answer is that's ridiculous.

Obviously the mic was hot with respect to ground or the pool was hot with respect to the grounded mic. Which and why we will probably never know.

This subject has been beaten to death both over in the Mike Holt forum and in the pro audio forums. Unfortunately this is only one of may such electrocutions caused this way.

Before anybody condems the sound system exclusively this is one instance where there could also be another cause.

These baptismals have heaters, lights and a pump. In my book that would make them a pool or spa yet I don't think they come under the applicable articles of the NEC though that might be a moot point. Keep in mind that houses of worship traditionally rely on congregants to provide the electrical and audio work.

In my opinion this is a recipe for disaster.

-Hal

To expand on that information, "phantom power" is supplied to a microphone over what is known as "balanced" audio lines. On the common three-pin connector on pro mics {known as "XLR"} the power is carried on pins 2 and 3 (+) and the negative (-) is on pin 1 (the shield of the cable.) It is a DC voltage, current limited, and anywhere from 12-48 volts. (48v being the most common.)

The normal connection scheme for balanced audio mics is Pin 1 = shield; Pin 2 = "signal hot" (or +); Pin 3 = "signal return" (or -). {Note that some brands of gear reverse the signal polarity of 2 and 3}.

A "dynamic" (does not need phantom power) mic is connected between pins 2 and 3 and thus does not see any voltage across the element if the phantom is accidently left on. (Both pins are at + vDC potential).

Since the (-) end of the phantom supply is tied to pin 1 , (and thus possibly to the chassis) it would be at the same reference as the chassis and the shield of the cable, and therefore the phantom could not cause a shock as described in the thread.

And if the (+) side of phantom shorts out to shield, the supply in virtually all gear shuts down to protect itself. (That's in case a mic where pins 3 and 1 are tied together in an "unbalanced" arrangement, which obviously creates a short across the supply.)

Hal brought up a great point, that the pools have heaters, filters, lights etc. any one of which could have energized the pool.

So a properly connected mic, with a mixer or amplifier in proper working order, may have actually provided a ground path in this case.

Like Hal said, we may never know....

mxslick
quote:I wonder if some of these cases might be caused by the "phantom power" supply required for electret mics.

I was wondering when someone was going to bring that nonesense up. Answer is that's ridiculous....

I hate it when people think I'm more ridiculous than I actually am. On background, I have been Chief Engr. & Maint. Supr. of 2 major market UHF stations and part of the design / build team of a place called Beachwood Studios. I did not mean to express or imply that "phantom power" could be the cause of an electricution! In a perfect world, pastors don't get zapped and musicians don't french kiss mics. I did mean to say that I wouldn't rule out the possibility that a phantom supply could cause a tingle similar to placing your tongue on a battery.

In this case, it would still seem most like ly to me that he was the victim of a hot chassis on a transformerless PS piece of audio gear with a polarized plug. The waveform that killed him would not be a nice sine wave. On his way to Heaven, he probably experienced CROSSOVER DISTORTION!!! <Nyuk,Nyuk>

Ohhhh thats bad!

-Hal

Hi Joe:

Hope you didn't think I was trying to imply you were being ridiculous, I was quoting someone else to expand on thier comments.

I hope my explanation of how a phantom supply works was accurate...

I like the testing method you suggested in your first post...it would still leave open however which source the voltage was coming from, the pool or the mic...of course, if you tested each to a known ground than the answer would be clear.

Crossover distortion, that was bad!!

Well Joe, you did say that you wonder if some of these cases might be caused by the "phantom power" supply.

Mxslick gave an excellent description of what phantom powering is and how it is applied so you can see why it couldn't be an issue with electrocution.

Edit: Oh yeah, I really do like the idea of someone walking around with a voltmeter before a performance or just periodically checking for leakage or voltage on the mics and instruments. Should be made mandatory!

-Hal

[This message has been edited by hbiss (edited 11-10-2005).]

I didn't get my feelings hurt folks & I understood how I could've been misunderstood. The posts got pretty divergent and I was responding to parts of a couple of them.

I do agree that you would have to have a pretty messed up mic(and musician) to touch both ends of the phantom supply with moist body parts.(Nor would I pay to watch a movie showing such a thing)

I don't recall the article saying, but it is quite possible that this fatal shock didn't damage a single piece of equipment. I find it very hard to believe that he provided a path to ground for installed equipment. This should be no mystery to local authorities if they took control of the accident scene and have the equipment. It would be extremely easy to reproduce the conditions.(except for the Assistant Pastor's part)<G>

There was other talk about zaps, hum, 3rd harmonic and the like. Remember to avoid letting the cases of your XLR(3 pin happy face) connectors touch concrete floors. Ground loops are a common source. If your noise source is 3rd harmonic, it shouldn't sound like 60 Hz. For my band, I would choose the members whose families were most likely to sue me first. Then, I would plug their amps into isolation transformers and tie their chassis into a star grounding scheme. But seriously, I would not let a hot chassis situation go because anything that zapped you, might have been able to kill you.
Plus, it is most likely causing distortions in your audio path now.
Joe

I just want to add that mxslick did do a very thorough explanation of phantom power. He did mention that the phantom supply will shut down to protect gear. I'm thinking that most probably keep operating but have sufficiently high output resistance that they just get pulled down to near zero volts across the load.

I also wanted to add that I found these forums by accident. You're an impressive bunch of folks with probably centuries of combined experience. Thanks for making me feel welcome here!!!
Joe

Aw, shucks, Joe, now I'm blushing...thanks for the compliment!


And oh yeah, welcome aboard! You'll find a lot of great info here too. Don't be afraid to browse the archives of all the threads (using the page numbers at the very bottom of your screen when looking at a selected topic area) there are a lot of older topics that are really informative!

[This message has been edited by mxslick (edited 11-12-2005).]

Some light reading of the big book... and I came across this gem...

I've not seen a phantom power circuit that's designed to shut down. Normally, they just have a 6800 ohm (IIRC) resistor in series with the 48V phantom supply before it connects to the mic connector.