Re: SHOCKING!

[Mike Curtis <wd6ehr@xxxxxxxxxx>]

<Stuff about mic shock deleted>

Tim's absolutely correct - when you're hot and sweaty, and you get across
an inproperly grounded situation (mic and guitar, harp mic and PA mic,
single piece of equipment and wet floor, etc.), it can be much more than
just an unpleasant experience.  It's a good way to get a new job at the 
cemetery pushing up daisies. 

Tim mentioned 200 milliamps.  Actually, the figure is far less.  I'll look
it up, but recall it being around 6 milliamps to cause cardiac arrest. 
Whether this is 6 mA through the heart or 6 mA period, I don't know off
hand, and will also research.  I usually don't post before research, but
this is serious enough to warrant a few possibly errant numbers.  That's
.006 amps.  At 117 volts AC, a body resistance of 20,000 ohms will permit
that much current.  Of course, how much of that gets channeled into the
heart is another question, and is dependent on many factors. 

ELECTRICITY 101

What is "voltage"?  Current (amps)?

Electricity is similar in concept to water, except it uses electrons 
instead of water.  The pressure that makes it flow is measured in volts.  
the amount of electrons that flows is called "current" (yup - just like a 
river current!), and is measured in "amperes", or "amps" for short.  If 
it's less than an amp, we use "milliamps (1/1000 amp) or "microamps" (1 
millionth.)

When you have more pressure (volts), more electrons flow (amps.)

Electricity always requires at least two "terminals" to complete a
circuit.  I can hang onto a 100,000 volt power transmission line with one
hand and not feel a thing.  The problem comes when I grab the other half
with the other hand!  If you've ever wondered how birds could sit on power
lines, now you know.  (Great for impressing kids and band broads :-) This
is why you don't get shocked until you touch two electrical sources.  Of
course, you may not realize them as electrical sources.  When I was a
child, I used to get shocked when I touched both the stove and
refrigerator at the same time. 

The most lethal path is opposing hand/foot, e.g. left hand/right foot, or 
right hand/left foot.  But even a hand/hand, hand/head, etc., can be 
lethal. 

The worst voltage is 440 volts.  Anything higher tends to flash over the
skin, causing surface burns but not as bad internal damage.  Many workers
at Southern California Edison (and I'm certain every other power utility)
have survived 220 kV and 440 kV (KiloVolt= 1000 volts) accidents.  Due to 
the surface effect, they're often referred to as "flashovers".

Anything over 48 volts is considered to be hazardous under normal
conditions.  However, lower voltages can be lethal under proper
circumstances. 

WHAT CAN I DO?

One handy piece of equipment is an electrical outlet analyzer.  You can
get a cheapie from Radio Shack (22-101, $5.95).  It's a little AC plug
with three lights (LEDS), and it will let you know if the socket you are
testing is properly grounded.  Unfortunately, a lot of nightclub stages
are wired by Atila the Hun and his assistant, Foghorn Leghorn.  If this is
the case, find a good outlet elsewhere, run a HEAVY extension cord to it,
and run ALL of the band equipment from this. 

If the outlets are 2 prong, use a 2 prong to 3 prong adaptor (you DO carry
a handful of these, don't you?), and CONNECT the little wire to the wall
plate screw, and CHECK IT with the outlet analyzer.  NEVER, NEVER break
off the grounding prong on your equipment.  It's there to save your life! 

A cheap voltmeter (i.e. Radio shack 22-212, $15; their cheapest one) is a
good way to make sure there are no voltage differences between different
equipment.  Set it to 120 volts AC or greater (300 volts is fine), and
check grounded metal parts of the audio jacks, e.g. the nut on 1/4" 
guitar jacks, mounting plate of XLR mic connectors, the outside shell of
RCA jacks, etc.  You will probably have to experiment with ground switches
on amps. 

You may find SMALL differences.  This is normal.  But if the differences 
are greater than 10 volts, try to find out why and correct it.

If you're playing on a metal or concrete surface, test between it and
other equipment as well.  And if the floor gets wet, don't bother testing. 
Just get it dry immediately! 

A ground fault interruptor (GFI) power strip is a very good investment,
and could possibly save your life.  This is like a circuit breaker, but it
looks for any ground current (there should NEVER be ground current), and
breaks the circuit should any be detected.  If it keeps tripping, you're
likely plugged into bad wiring, or maybe someone has their ground switch
set wrong.  Radio Shack doesn't carry these, but you might find them at 
construction supply houses.

SUMMARY:

1. Use an AC plug tester to make sure the socket is wired correctly.

2. If possible, use a GFI equipped power strip or junction box.

3. Always use a properly grounded outlet, even if you have to install an
   adaptor and connect the wire to the center screw.

4. Use any voltmeter (set to 120 volts AC or greater) to test for voltage 
   differences between component grounds.

5. When playing electric instruments, water is your worst enemy.  If the 
   stage is wet, or if something gets spilled inside an amplifier, etc.,
   shut down and fix the situation before continuing. 

6. It's good if you run all band equipment from the same electrical wall 
   outlet.  This will "common" the grounds for all equipment to a single
   point (which is good.)

7. Carry a long extension cord - maybe 100 feet or more - in case your 
   stage electrical is not up to electrical code.

8. If you find stage electric that doesn't pass the "socket tester", 
   either report it to club management, or to the city building inspectors
   if you're worried about club management being more concerned about
   money than life, blowing the gig, etc.


                           -o-

I used to work as a communications technician for Southern California
Edison, one of the local power utilities.  We had monthly safety meetings,
many covering electrocution and related topics.  Even though I worked with
telephone systems, microwave baseband, and telephone/data distribution
(they have their own in house telephone system serving their many
facilities all over California, with more than 10,000 different telephone
numbers), I was still in the position of being exposed to high voltage
environments.  Our telephone cables were often run under 220 kV and 440 kV
transmission lines, which induces some downright nasty voltages into the
lines.  We measured one trunk cable at 10,000+ volts!  (And yes, it could
deliver more than enough current to provide an all expenses paid trip to
Forest Lawn.)


 -- mike