Newsgroups: rec.arts.theatre.stagecraft
Subject: Re: Sound System electrocution
References: <[email protected]>
Eric N Johnson  writes:

> This incident was covered in a number of media outlets:
> 
> http://www.cnn.com/2005/US/10/31/pastor.electrocuted.ap/index.html
>   WACO, Texas (AP) -- A pastor performing a baptism was electrocuted
>   inside his church Sunday morning when he adjusted a nearby microphone
>   while standing in water, a church employee said.
> 
> What could cause this?  I know one posibility is if the system is not
> properly grounded, but are there others?  

One possibility is that the system is not properly grounded. 
The electrocution was caused by some mains voltage (due bad 
grounding) on the microphone metal case... that going through 
the person to water that has some ground connection. 

Other possibility if there are lights or something in the 
water is that there is some device on the water (for example 
damaged underwater lighting, water pump etc..) that makes 
the wate to become at mains potential. Standing just in the water 
does not kill you but touching something that i heavily 
grounded will ause lethal voltage through you.

> Can phantom power become dangerous
> if the current limiting is not functioning properly?

The phantom power uses 48V DC voltage that is limited to 
somethign around 10 mA. This voltage and current can give 
you electrical shock if you are stading in the water. 
Maybe in very unfortunate case could kill... 
Not highly propable though, because phantom power is DC 
that is less dangerous than mains frequency AC. 

> Does anyone recommend the use of GFCIs (or similar devices) on sound
> systems?

Using GFCI is a good idea on sound systems if they are used 
in dangerous situations. I routinely use GFCI on those 
case where I need to run the sound system on dangerous 
locations (outside locations, inside old buildings where 
there is no grounded power available etc..). 

Using GFCI can save you from electrocution. 
The downside of using CFCI is the system reliabity, 
GFCI can sometimes trip for strange reasons withtout 
real problem and at some inconvient time... 

When you are in dangeous location (everywhere near water) 
I recommend to routinely check the quality of electrical 
installation (everything connected correctly, ground 
connection is not cut etc..) and use CFCI to protect people. 

And then I would heavily recommend to consider using 
wireless microphone when you are using microphone when  
you are talking from water! Wireless microphone is completely 
isolated from everything else, so touching it does not 
get you electrocuted in any case whatever the environment. 
The wireless microphones are inside low voltage devices 
(typically powered with 9V batteries), so they will not 
be dangerous even if you happen to touch the inside electronics 
or drop that microphone to water (will most propably ruin the 
microphone bu no danger to user). 

> It's a truely unfortunately incident, horrific for the entire
> congregation.

According the article:
"Water in a baptistery usually reaches above the waist"..

Water and electricity are a very dangerous combination. 
I would be very worried in using microphone while standing 
in the water. It is potentially very dangerous if anything 
is wrong in the sound system. I think that in this kind 
of environment the safety should have been though more 
carefully in the beginning. 


-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/