[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: Terrified Parents



Original poster: "Stephen Mathieson" <s.mathieson-at-charter-dot-net> 

I too have had an experience with traveling wave tubes (in an AN/SPG 55B
Mod3) that literally knocked the %$&!*$^% out of me.

The incident with the Simpson meter is not an urban legend. It happened at
Baylor Company, Sugarland, TX around 1993.  We had been doing R&D (repair
and destroy) while developing controls for a 1000KVA hybrid on-line rotary
UPS. We had a low voltage on one leg of 480 and the maintenance dept.
thought they could fix it as the maintenance / safety manager was licensed
as a "master electrician."  HV probes have max voltage ratings, this was
ignored. They are in fact a voltage divider, which in this case was not
properly grounded. Without the ground the "divided" or low voltage output
going to the Simpson meter was equal to the applied voltage of 13.2KV with
the shortest path to ground being through the screw holes in the back of the
Simpson, through the assistant and out his back to the metal light pole.
Since the HV probe was not rated for 13.2KV current was not limited and the
assistant was killed instantly.

The problem was eventually traced to a bad PFC cap on one leg of the 13.2KV

Always have a safety "observer," there was no reason for the assistant to be
holding the meter. Also, "floating" a scope is an unacceptable practice when
it comes to safety, make a HV measurement differentially using two channels.


Stephen A. Mathieson

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Saturday, November 29, 2003 7:33 PM
To: tesla-at-pupman-dot-com
Subject: Re: Terrified Parents

Original poster: dhmccauley-at-spacecatlighting-dot-com

Definitely an urban legend.  HV probes always have dividers built in them.
Thats the whole purpose of a HV probe.   If it didn't have the divider, it
would basically be
just a metal rod with an insulated handle.

However, i do have a story that is true.  A technician at my company was
working with a radar transmitter in the high voltage cabinet, and was taking
oscilloscope measurements from a
modulating high voltage deck.  The deck itself is low voltage (28VDC with
+/-1000VDC for the grid modulating system), but the entire deck is floated
at the cathode voltage of the TWTs
which is about 45-60kV depending on TWT.  Anyways, the oscilloscope was
being floated on top of the deck to measure something in the deck, and the
technician went to change a setting
on the scope and . . . well . . . you can imagine what happened next.

Dan

  > Sounds like an urban legend to me. Aren't most
  > handheld Simpson meters "low" voltage (<13 kV)? Every
  > HV probe I've encountered was a voltage divider.
  >
  > Adam
  >
  > --- Tesla list <tesla-at-pupman-dot-com> wrote:
  >  > Original poster: "Stephen Mathieson"
  >  > <s.mathieson-at-charter-dot-net>
  >  >
  >  > Terror is your friend. I have been coiling for a
  >  > number of years thought and
  >  > dealing with high voltages much longer. Nothing
  >  > compares to seeing a Master
  >  > Electrician attempt to measure 13.2KV with a HV
  >  > probe, gauntlets and the
  >  > works, but his assistant was holding a Simpson meter
  >  > and leaning against a
  >  > light pole. The arcs came out through the screws in
  >  > the back of the meter
  >  > and the current blew a 12" diameter hole in the back
  >  > of the assistant
  >  > killing him instantly.
  >  >
  >  > As I said, terror is your friend. You can overcome
  >  > it but it will always
  >  > make you think twice about what you do and what you
  >  > touch. Terror can help
  >  > keep you safe!
  >  >
  >  > Stephen A. Mathieson
  >  >
  >  > -----Original Message-----
  >  > From: Tesla list [mailto:tesla-at-pupman-dot-com]
  >  > Sent: Friday, November 28, 2003 9:35 PM
  >  > To: tesla-at-pupman-dot-com
  >  > Subject: Re: Terrified Parents
  >  >
  >  > Original poster: Tesla729-at-cs-dot-com
  >  >
  >  > In a message dated 11/28/03 7:02:46 AM Pacific
  >  > Standard Time,
  >  > tesla-at-pupman-dot-com writes:
  >  >  >All figures available at
  >  >
  >  >
  >

 ><http://www.cpsc.gov/library/data.html>http://www.cpsc.gov/library/data.htm
  >  > l
  >  >  >
  >  >  >So... statistically, Tesla coils have a better
  >  > safety record than consumer
  >  >  >electronics, trampolines, and candles.
  >  >  >
  >  >  ><In fact, every job, hobby, sport, activity, or
  >  > just
  >  >  >about anything worth doing carries a certain
  >  > amount of
  >  >  >risk. Tesla coiling occupies a pretty low spot on
  >  > the
  >  >  >risk scale, way below skateboarding, woodworking,
  >  >  >cycling, swimming, football, or even driving a
  >  > car.>
  >  >  >
  >  >  >Absolutely!!
  >  >
  >  >
  >  > Hi all,
  >  >
  >  > Yes that's very true but you also have to realize
  >  > that there is
  >  > relatively very few people that play with Tesla
  >  > coils, probably
  >  > less than .01%  of the general population. .01% of
  >  > nearly 300
  >  > million US citizens is still like 30,000 and I
  >  > seriously doubt that
  >  > there are 30,000 active coilers in the USA. I'm sure
  >  > that there
  >  > is a MUCH higher % participation in the other "more
  >  > hazardous"
  >  > activities (mowing grass, burning candles, driving a
  >  > car, ect.) than
  >  > there is in coiling. Since so realtively few people
  >  > practice coiling, there
  >  > is consequently few incidents. I'm sure that most
  >  > coilers playing it
  >  > safe does go a long toward keeping the accidents
  >  > low, too, though.
  >  >
  >  > David Rieben
  >  >
  >  >
  >
  >
  > _