Re: Dont get zapped.

To: tesla-at-pupman-dot-com
Subject: Re: Dont get zapped.
From: Terry Fritz <terryf-at-verinet-dot-com>
Date: Thu, 10 Sep 1998 18:42:24 -0600
Approved: terryf-at-verinet-dot-com
In-Reply-To: <7110.9809101056-at-quartz.kbss.bt.co.uk>

Hi Julian,

At 11:56 AM 9/10/98 BST, you wrote:
SNIP........
>
>Be aware of variacs and neon sign transformers, I got careless and a zap.  
>The variac was turned all the way down, neon sign transformer plugged in and
>I made an adjustment to the spark gap - ouch.   The varaic was outputting 
>2 volts and through a 1:50 transfomer this harmless voltage is stepped up to
>100 volts.  
>

Beware that variacs are NOT isolated from the AC line.  Even though the
voltage on the output may be zero between the output wires, the output
wires could easily be floating at 120 volts above the ground potential.
This is the case when the HOT wire is connected to the common of the
variac's windings.  You should have the neutral wire connected to the
common wire of the variac.  However, always switch off all the power before
working on the system.  It is too easy to get between the HOT AC line and
the grounding of the system.  The off switch should switch both the hot and
the neutral wires to insure that the system is totally isolated from the AC
line power no matter what.  I have a red light bulb (25 watt) hooked across
the variac's input so that there is a big red light glowing whenever the ac
is present.

It is easy to check if the variac is wired properly.  Apply power to it but
have the voltage turned to the minimum.  Connect an AC voltmeter between
the outputs and ground.  You should read a very low voltage like 1 or 2
volts.  If you get 120 volts, reverse the input wires. 

Also, beware that most switches only switch one side of the AC line which
SHOULD be the hot wire.  If your wiring is reversed somewhere, it would
allow the hot wire to stay live presenting a danger as you work on the AC
side of the system.  Always pull the plug!

	Terry