A not so gentle reminder - HV is unforgiving

[Sandy W5TVW]

        I read Dave's story and cringed thinking of a similar happening I
had!  I was doing a job on a ship transmitter and had no indication of any
plate current on the panel instrument.  This was a kilowatt rig with around
2900-3000 volts of B+ on the final anodes.  For a quick check, I switched off
the rig and pulled the interlocks. I then hooked my little Triplett meter in
series
with the high voltage (via the "Millen" connector on the rear of the RF deck),
and stood off the little meter with a couple of thick manuals for some "safety"
insulation in case the meter case decided to 'flash over".  Turned everything
back on and verified that there was some idling plate current.  Shut things
down, pulled the interlocks again, waited a few minutes and then proceeded
to disconnect my meter when....ZAAAAaaaaappp!  the "hammer" hit me hard!
Then the smell of burning flesh and plastic!  I looked and found three places
on my right hand that looked like moon craters surronded by blackened skin.
They burned like hell.
        What happened?  My first mistake was not to pull the main circuit
breakers on the three phase supply to the Radio Room.  This was a
foreign flag ship and the arrangement of the electrical equipment was
typically different, and I didn't bother to find out where the main breaker was.
        Why did I get jolted, in spite of pulling the interlocks?  Becuse the
damned main contacter relay's contacts that supplies the three phase
to the HV transformer's primary had stuck in the energised position!
Even though the control circuits AND interlocks were off, the relay had not
dropped out!
        Why didn't I short the HV to ground before I removed the leads of my
'little' meter?   Good question!  Probably because I'd worked on so many of
these rigs, that "familarity had bread contempt" had prevailed.  This wasn't
the only jolt
I've gotten, but surely the worst one!
        Fortunately, I didn't suffer any other ill effects.  One of our
techs got
electrocuted in a similar situation while working alone, as nearly all us ship
radio techs do, when working on radio room gear.
        I *SHOULD* be aware of all the precautions, as I cut my teeth on tube
gear before there was any "solid state" stuff!  I ignored some of the things
I shouldn't have!  One *MUST* be careful around high voltage.  It sits there
sometimes very silently waiting to strike the careless like a coiled snake.
As the old QST line used to go: "SWITCH TO SAFETY".  Your linear's
power relay may hangup someday, waiting to give you the jolt of your
life!  Maybe the last jolt!  BE  CAREFUL!
73,
Sandy W5TVW

--- --- --- --- --- --- --- --- --- --- --- --- --- --
To subscribe: listserv at listserv.tempe.gov
and in body: subscribe HEATH yourfirstname yourlastname
To unsubscribe:  listserv at listserv.tempe.gov
and in body: signoff HEATH
Archives for HEATH: http://www.tempe.gov/archives
--- --- --- --- --- --- --- --- --- --- --- --- --- --