Re: Preventing a REALLY expensive mistake.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gary Johnson by way of Terry Fritz <twftesla-at-uswest-dot-net>" <gjohnson-at-ksu.edu>

>
>Doesn't a Faraday cage only work if it's a COMPLETELY ENCLOSED room? I don't 
>mean airtight (but there is a specific maximum size hole for a given 
>frequency protection limit)?
>

Christopher:

You have been getting some good advice on this issue. Just thought I would
add my experience. I built a large ag-type building (a Morton Building) to
do my Tesla coil stuff in.  It has roof and outside covering of a steel
sheet metal. I built a room in the corner of this building that I could heat
and cool. It is also covered sides and top with steel sheet metal. Think of
a steel box inside a steel box. Inside the room I have a double wall copper
screen room, 8 by 10 ft by 8 ft high. (The local EE Department was throwing
it away.) My computer and scope are inside the copper screen room while the
Tesla coil is out in the large bay.  Screen room power comes through a 5 kVA
transformer. It is not specifically designed as an isolation transformer. I
am not doing medical research or building an surgery facility for which a
true isolation transformer becomes more important. I just want my scope to
survive whatever the Tesla coil is doing 15 ft away. The main function of
the transformer is to separate the local Tesla coil ground from the utility
ground. The screen room and the equipment inside are all connected to the
local ground.  I disconnect the phone line from the computer when the coil
is running. I don't know how much of this is necessary, but I have not lost
any electronic equipment due to electric or magnetic pulses from the coil,
to my knowledge.

In specific answer to your question, I use a transistor radio to check the
effectiveness of the screen room. The AM radio receives a full range of
stations inside the airconditioned room but outside the screen room. Steel
sheet metal on four walls and ceiling has little effect on reception. Maybe
the signal is coming up through the concrete floor? But as I carry the radio
into the screen room, by the time I am 3 ft inside, it is dead! Just static.
This is with the heavy copper door still wide open. So I never bother to
shut the door when the coil is operating.

Anyhow, based on my one data point, I would be concerned about chicken wire
or any other simple, cheap, quick and dirty scheme using steel sheet metal
being of substantial help.

Gary Johnson