Mike

Unfortunately, many "pro sound" amplifiers have "ground lift" PUSHBUTTONS on them - in many instances, a small pushbutton located on the back panel of the amp (I have two at home which have exactly this). So even if the ground wasn't intentionally lifted for noise reduction purposes, it's all too easy for the button to be depressed without anyone noticing.

I'm in a weekend gigging band; hot mics are rare, but they do happen (Gary Thain of Uriah Heep took a nasty shock on stage from one). One thing my bunch has always done is to plug in all the amps, PA, etc. through GFCI "pigtails", which are all tested before every gig. If it trips during a song (which has not yet happened), far from being upset about it, we'll be glad it was there to protect us.

It would seem that, regardless of mic or grounding issues, a properly working GFCI on the sound system AC supply would have detected the current leakage into the pool, and interrupted the voltage, saving the pastor.

Very sad indeed.

Your statement "A common practice in the Audio industry is to disconnect the ground wire (what is really a bond wire to the power system) so that they can reduce the 'noise' on the sound system." is totally incorrect. While some amatuer or well meaning hobbyists might think this is the solution to noise, the professionals in the sound industry are sincerely dedicated to safety and know that the removal of the bond or safety ground is unacceptable and is never done. There are ways hum and other noises can be removed. Balancing transformers are but one example. Lifting the shields from one amplifier to another is also done, but in neither case is the Green "SAFETY" ground wire removed from the active component. In the case of the event in Waco, the heater/pump assembly in the baptistry was improperly wired, the ground disconnected and no GFCI installed. In fact the "Correct" grounding of the sound system was the ground connection the AC used to complete the circuit that resulted in the death.

I feel the sound professionals I work with and are associated with deserve an apology for your earlier comments about grounding.

re: Mike's reply to my reply to his reply....

Mike,

Quite the contrary. The shield on a microphone cable will be connected to signal ground, which, in a properly installed system, will be connected to chassis ground.

I may have misinterpreted your initial comment. I took it as referring to breaking the shielding on audio cables, but I think now you must have been referring to breaking the green wire grounds. Most of my comments have been aimed at signal cable shields.

That said, I don't see a it as reasonable that fatality was caused by lifting a green wire ground. Maybe if this had been bar band equipment or an amp/mixer combo for a small venue, but the information in the press (800 people in attendance, David Crowder as a founder) indicates to me that this would be a professional installation with many components. If that is the case, floating the sound system relative to ground would be difficult -- there are too many interconnecting cables, pieces of equipment bolted in racks (generally with wiremold plug strips bolted the the rack and/or conduit connections, which would effectively ground the rack), etc. Even if the green wire ground on the console's power supply was disconnected, intentionally or otherwise, there would still be multiple paths to ground via the audio cables. I just can't envision an energized console chassis as the voltage source in this case.

The latest reports say that an investigation is in progress. This one will be worth watching.

Martin

P.S. This is a good reason to use wireless mics around baptistries.

You would still need to bond the reinforcing steel that is in the walls of the pool. This is to intercept current that is flowing through the soil such as from a downed power line or a failing underground 120 volt circuit. In 2005 NEC language was added to require nonmetallic in ground pools to have an equipotential grid around the pool to shield the pool from electricity that is flowing through the soil. My experience with tingle voltages shows that you also need an equipotential underneath a nonmetallic pool.

The first time that I had to troubleshoot a nasty tingle voltage involved an ordinary bathtub with a nasty tingle voltage between the drain and the faucet. The basement washing machine as well had a nasty tingle voltage even though it was PROPERLY GROUNDED. The mechanism in this case was a failing underground rigid metal conduit going out to a detached garage. This was leaking 7 amps at 120 volts during a DROUGHT! In the course of returning to the water service this flow of current was energizing the drain pipes and the basement floor. It was neither the faucets nor the washing machine that were hot but rather that the user's feet were hot.

Since the underground metal conduit and the water service were about the same length most of the distance from the conduit to the water service would have been around 40 to 80 volts. This is because about 1/3 of the resistance of a ground rod occurs within 3 feet of the rod hence the 6 foot spacing rule. Fortunately, the bathtub and the washing machine were close to the water service. The kitchen sink, which was close to the deteached garage, had to have some type of ad hoc bonding between the water supply pipes and the drain pipes otherwise there would have been a serious electric shock hazard.

What I had to do to get the tingle voltage out of the bathtub was to bond the cold water pipe, the hot water pipe, and the drain pipe to each other and the main grounding electrode conductor for the electrical service. What I had to do to get rid of the tingle voltage was to cut the power to the detached garage - the tenant's son kind of liked to walk around the basement in bare shoes.

One other symptom was that this house which had gas space heat, a gas water heater, and a gas stove was that the electric bill was around $200 to $500 per month!

These microphone accidents have happened so many times in the past. Being that the microphone is connected to an amplifier, which is an inductive unit, I wonder if the shock from such a thing is much nastier than a regular shock.

re: Mike's reply

Mike, I respectfully disagree that a fault in a sound console will cause 120V to appear at a microphone case if the mic ground was lifted.

Assuming professional quality equipment in good condition and with balanced signal configuration, for a dynamic mic there should be no connection between the signal conductors and the mic case. Even if there is a short to case in the mic there are isolation capacitors, loading resistors, and many other electronic components in the circuit. Any fault in the console that could overcome the input circuit configuration and energize the mic case with 120VAC would cause so much noise in the system that it would be unusable, and/or would destroy the electronics in the console or blow the fuses in the console. There is no low impedance connection from signal leads to the ground plane in any sound console I've ever build, repaired, or evaluated the schematics of. A fault in the sound console power supply might energize the console signal ground plane at 120VAC, but the voltage path to the microphone would then be over the shield, and your working assumption is that the shield is intentionally broken, which would break the voltage path.

Phantom powered mics do have DC voltage returned on the shield, but they don't work without an intact shield.

I realize none of us have been on-site to evaluate the actual installation, but in my opinion this has to be a fault in the pump/heater system. The fault modes that I'm aware of in a modern sound console don't support supplying 120VAC to a microphone case. In the absence of data from a field investigation by a trained professional, I have to believe that an intact, proper shielding system on the microphone and cable provided a conductive path to ground rather than multiple defects in the sound system somehow energizing the microphone case. I understand how an untrained observer (thinking of media reporters here) might jump to a conclusion that the mic must have been energized, but I see no field data or measurement that supports that conclusion, and my experience, both with sound systems and as a PE who does building electrical system design, leads me to a very different conclusion.

I stand ready to be proven wrong.

Martin Shoemaker

Getting shocked by a 1.5 volt D cell essentially proves that any voltage that is hot enough to light a light bulb is a hazardous voltage if you are wet enough and salty enough.

The audio cable shields would still need to be bonded to both the electrical service ground and the reinforcing steel in the pool as well as the pool pump. One way to get a low noise ground for the shields is to use a 4 -prong plug that provides 2 isolated read shilded equipment grounds, one for the equipment frames and the other for the cable shields. Both equipment grounds would need to be connected together at the service and the branch circuit would need to use a metal enclosed wiring method that would shield the equipment grounds from acting as antennas for noise. If you try to implement an isolated ground circuit using romex of PVC conduit the isolated ground will ge just as noisy as the regular equiment ground unless what you are using is a shielded nonmetallic cable such variable frequency drive cable.

Mike Cole, mc5w at earthlink dot net

One of the things that I have learned the hard way ( back when I was kid ) is that it is possible to get a nasty electrical shock from picking up a 1.5 volt D cell by the ends. This was back when I would play with my electrical stuff for hours without washing my hands and if I built up enough perspiration salts on my hands skin resistance would drop like a rock. Since then I wash my hands frequently which actually keeps my skin resistance high enough that 480 volts merely hurts a lot. Some people are somehow more resistant to electrical shock than others and I have met people who can barehand 120 volts. On the other hand, grandmother was someone who could not let go of 120 volts.

Getting shocked by a 1.5 volt D cell essentially proves that

Unfortunately, it is sometimes forgotten that these baptismal pools need to be treated as a swimming pool if somebody is going to get into it. My experience with getting rid of tingle voltages shows that the source of hazard current can be failing underground wiring on a neighboring property.

The same thing situation almost happened with the new mikvah bath over at Revere Road Synagogue in Akron, Ohio. Sombody forgot to install a bonding wire for the reinforcing mesh of this bath and after I pointed out what was wrong either the concrete contractor or the electrical contractor had to saw into the concrete and hook up a bonding wire.

However, what really gets me is that the Summit County electrical inspectors are very strict about bonding and grounding of swimming pools but they allow aluminum SER cable to be used for a panelboard feeder for a swimming pool or hot tub in NEW INSTALLATIONS!

Mike Cole, mc5w at earthlink dot net

I have to agree with those how have said that it is unlikely that this was a problem with the sound system. If the sound system was "floating" and supplying lethal voltage on the microphone shield relative to ground the musicians and the sound board operator would surely have been "shocked" during normal operation of the system. This almost has to be a problem with the pump or water heater (or a related system) energizing the water, with the sound system providing a return path. That implies that the sound system was in fact properly grounded. If the sound system grounds had been lifted there would have been either no ground path, or at worst a very high resistance return path through the electronics in the sound board.

There may have been a needed polarized plug somewhere in the system that had been replaced with a non-polarized one that could have been the culprit. It was very tragic in any case. My sympathy goes to his family.

You don't need to use the Equitec systems to get a noise less sound system. In reality in a very large audio system the Equitec cqan actaully contribute to the problem. A properly design system with all the grounding connected and everything properly bonded will be both safe and noise free. In this instance I'll bet your right that someone cut the ground pin from the plug. I run into this very often, its always followed the line "we have a guy in the congergation whos good with sound that make it work". Usually it the one with the largest home stereo. You should look at the tech notes put out by audio companys such as at www.rane.com, www.benchmarkmedia.com and www.jensentransformers.com. They have lots of info avaiable on how to maitain a safe and noisless signal pathe without ever lifting the power ground. There is an orgization called Syn-Aud-Con (www.synaudcon.com)that offers trainig in proper design of systems and they stress the importance of the saftey bonding.

Hello Mike. Thanks for your comments and forum comments. I have learned many things from your site. I am an Electrical Contractor in Abilene, TX. Both my daughters ar at Baylor University in Waco, TX. My wife, daughters and I were attending "their" church in Waco the morning of October 30th., which was University Baptist Church where Pastor Kyle Lake was electrocuted, within 30 feet of us. I have been trying to make sense of all this. Thanks again for your educational articles. Maybe readers will take this knowledge, apply it and hopefully some other lifes will be spared. Be Blessed... Jerry Weems

If the pool water was at line voltage than the microphone ground will complete the circuit thus the deadly current. However the pool should had a GFCI installed, was it?. The pool GFCI would have tripped off in ample time to prevent the electrocution. If the microphone shield got shorted to the line power hot than the person who handed the microphone to the pastor would got a nasty shock. Bands do not like GFCI's because it could trip off during a performance. Some microphones have an enable switch that may have been faulty. When the pastor pushed the switch ON... then!

Les Vass WWW.TESTEQUIPMENT4UL.COM

To me, it doesn't semm plausible that the microphone supplied a high enough voltage to electrocute someone. I believe there must have been a water heater in the pool or attached to the pool through metal pipes. The pool was probably not grounded (fiberglass) and the water was probably energized already from a faulty element and when the pastor touched the grounded microphone he completed the circuit.

Hard to believe, something is missing... microphones are either passive or have a 'phantom power' that's 48Volts, mostly harmless for use in a pool...

THANKS FOR SHARING WITH US THE UNTIMELY DEATH OF PASTOR WACO .I AND MY FAMILY WISHES DEEPLY FELT CONDOLENCES TO JENNIFER AND THE FAMILY .

A very real and disturbing article. What should have been a birth by baptism turned into a real tragedy. How often one walks around only see the "equipment grounding (bonding) conductor" removed from either equipment or cords. Education, the key to helping eliminate such a tragedy from ever happening again. One often believes they understand Article 250 but after 20 years in the role of inspector/instructor the one that I have learnt is constant vigilance on Article 250 is a must. From Inspectors/Installers/Teachers Article 250 is one of the most misunderstood Articles in the NEC.

Any thoughts on 640.10 (A) Of the code? GFCI protection would have saved this poor man I do know but I do wonder about nuisance tripping due to Integral transformers tieing XO to the frame of the amp.?

I'm not familiar with the actual fault circuit involved in this tragic incident, but it seems to me that a ground-fault interrupter on the amplifier's electrical outlet might have saved the pastor's life.

If this is the case, then it might be a great public service if one of us were to place a note in whatever religious magazines we can find. It would just say something like, "Pastors: if you use your microphone in baptismal services, be sure to install a 'ground-fault interrupter (GFI)' on the electrical outlet that supplies your sound system."

Then sign the note with your name and title. I'm sure that the magazine editors would be pleased to run such a notice, and it could be sent via e-mail. The magazine editor may also ask you for a few details.

What I may do is check with the churches around here and find out what church magazines the pastor has and make a list of their e-mail addresses, and then send the notice out to all of them.

I'd like to comment on the mailing regarding the death of a pastor in Waco TX. I feel for the congregation and the family. It is an unfortunate occurance, that likely could have been prevented.

The statement "A common practice in the Audio industry is to disconnect the ground wire" (edit) " so that they can reduce the 'noise' on the sound system."

I would like to argue the term "audio industry"... Any PROFESSIONAL sound engineer would NEVER disconnect the "ground wire" on the power cord of any audio equipment. Low-voltage (balanced audio) signal lines, are an exception, however, the equipment would still be (safety) grounded.

As a professional audio engineer, I come across MANY systems (some in churches, as well as other venues) that have equipment with the ground pin cut off from the power cords. Every time, I find that it is an untrained person who has done this to "fix" the problem.

Any person knowledgeable in sound systems can easily find the real problem, and apply a proper fix (usually an audio level isolation transformer).

Also, a properly designed and installed sound system should not need ANY ground "lifted".

To use the term "audio industry" is very misleading, and unfair, to the many competent sound people, who know better.

Thanks for your time, and keep the good work coming!

Sincerely,

Shawn Coppel

Hi there: Sad story re: pastor electrocution. Mike Holt's Comment: A common practice in the Audio industry is to disconnect the ground wire (what is really a bond wire to the power system) so that they can reduce the 'noise' on the sound system. For more information on the proper grounding (bonding) of sound systems, and the elimination of 'noise,'>>

While I have yet to view the link provided, it should be noted that a common practice to get rid of noise IN AN IMPROPERLY IMPLEMENTED, PERHAPS POORLY DESIGNED AND/ OR INSTALLED AUDIO SYSTEM, is to lift (disconnect) the electrical ground. It is also a common END-USER practice, once a sound system is installed, to add on to the system and not follow noise-free connection protocol, and then lift the ground in an effort to reduce noise.

Mike this is a very unfortunate event that does happen quite a bit, It has been one of my pet peeves that the manufactures have known about this problem but have done nothing in the design of their equipment to block this from being able to happen, By simply isolating the audio shielding from the supplying power circuit grounding would go a long way in preventing this. There is no reason to physically couple these two together. There are many audio system that use this approach in many applications, Almost all home audio systems do without any problems and they do not even have a equipment grounding conductor in there supply cord. Yes metal cases of professional audio equipment does have to be grounded to the power supply's grounding but the low level audio signals do not need this as we know that there are some cases where it will become a parallel path for neutral current which can kill, It is this path that also causes the 60hz hum that sound-men will lift or defeat the equipment grounding to eliminate. It is a very common problem that has gone on long enough and manufactures need to redesign there equipment to stop these unnecessary deaths. Here is a thread you might want to follow with as there are some good post in it. http://www.mikeholt.com/cgi-bin/codeforum/ultimatebb.cgi?ubb=get_topic&f=13&t=000766&p=2#000023

Sorry I missed you when I was down in Florida as my Aunt had a stroke and I had to get up there to Morehead City,NC. in a hurry. I would like to take to someone as to what training literature to buy from you to help in training real green electricians.