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

> Clive Mitchell  wrote:
> > I think there are a few on this list that would like to have examined 
> > that whole installation directly after the event.
> 
> Yeah, I'm one of those...
> 
> Interesting that the UK regs are moving towards fault current detection on
> sound system circuits.  I haven't heard of any similar pushes in the US, but
> I've not been looking either.  It makes a lot of sense to do so, although
> given the nature of sounds system, I wonder about the level of nusance
> tripping.  

Using fault current detection on sound system mains circuit is 
a good idea. Especially on the mobile systems that are 
moved from place to place often. It makes lots of sense to use them. 

> Here's an interesting question: Is there a way to structure a sound system to
> only disconnect a portion of it when there is a fault current?  Given that
> fault currents can flow through the screen/shield from device to device, it
> seems like you'd have to cut off the whole thing, or break it up into
> sections that were all isolated from one another (transformer or optical
> isolation).  

You don't need to cut the whole thing. The ground current in 
case of fault flows whatever route to gound it takes. 
The fault current detecotr that is powering the failed 
equipment trips, because that's where the current on live 
and neutral wires do not match. 

> Aren't most audio "isolation transformers" only rated for
> noise isolation?  I don't recall seeing a rated breakdown voltage listed
> for safely isoation applications.

Most  audio "isolation transformers" seem to be designed fro 
low voltage noise isolation. But there are also models that 
can handle higher voltags. For example Lundahl lists on their web site 
at http://www.lundahl.se/ models that have isolation voltage rating 
from 1.5 kV to 4 kV. I think there are other transformer 
manufacturers that have models with this kind of isolation ratings.

> I realize that no one likely knows what happened in that particular church.
> I'm using that incident to start a discussion, and to get people here
> thinking about it. 



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