Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ncar!noao!asuvax!mcdphx!mcdchg!ddsw1!corpane!sparks
From: sparks@corpane.UUCP (John Sparks)
Newsgroups: sci.electronics
Subject: Re: Electrocution -- Is this possible?
Summary: transformers can short from primary to secondary
Message-ID: <474@corpane.UUCP>
Date: 21 Mar 89 12:38:37 GMT
References: <7571@polya.Stanford.EDU> <7528@batcomputer.tn.cornell.edu>
Organization: Corpane Industries, Inc., Louisville Ky
Lines: 38

<19861@prls.UUCP>

In article <19861@prls.UUCP>, gordon@prls.UUCP (Gordon Vickers) writes:
>       Normally, the audio is coupled from the output stage of the amplifier
>    to the headphone jack with a transformer.  Normally when a transformer
>    faults, it is an open on either the prymary or the secondary side. An
>    electrocution would require that the transfromer shorte from primary
>    to secondary. Not unheard of, but very rare I beleive. 

Unless a transformer is wound with the primary and secondary on separate posts
of the same core, it is just as easy for a short to occur between the primary
and secondary as it is between each side alone. On most transformers the
primary and secondary are wound together on the same core post. So the wires
are lying side by side, a simple scratch could short them together. 

Also on most older TV's all circuits reference the same ground, that includes
one side of the AC line which is usually connected to the metal chassis.
The manufacturers used polarized plugs to make sure that the AC neutral wire
was the one use for reference. 

If the prison's outlet was wired backwards, or the polarized plug was replaced
with a non-polarized plug and was plugged in backwards, the metal chassis and
all of the d.c. circuits would have been referenced from 120VAC, since they
shared the same ground. If the transformer output was grounded on one side, or
if it used a transistor output, the electrocution would have been possible.

I got a nasty shock once while working on an old TV that didn't have a
polarized plug. I plugged it in and picked up the metal chassis, intending
to flip it over. BBBBZZZAPPP!! 

It was a shocking experience to say the least (pun intended!).

And don't make fun of my last name :-)
---- 
John Sparks   |  {rutgers|uunet}!ukma!corpane!sparks  | D.I.S.K. 24hrs 1200bps
______________|          sparks@corpane.UUCP          | 502/968-5401 thru -5406
 
186,000 miles per second: it's not just a good idea, it's the law.