Conference napalm::commusic_v1

    re .0	Insight No, but I have given it some thought.  Since
    one of my components arrived sans power cable (we had left it plugged
    into the wall at the store in our excitement to pack it up and get
    it home) I quickly grabbed my VT 100 cord, no luck cos its a three
    pin with ground type.  "Hmmm", I thought, "they must let everything
    float to avoid ground loops and hum".  Didn't think much more about
    it other than to check the stereo, no ground on that either, OK
    lets turn it all on.  I don't think I have hum problems, I guess
    I have assumed that there is a "ground at source only" rule, with
    thru being a source.  Len ?   Len ?   WaddYa think ?
    
    	Reg
    

Ground connections for some manufacturers:
    O=open Ch= chassis !=hmmmmm
    p2= pin 2 of midi connector     shl= shell of midi connector

		MIDI IN	   MIDI OUT   MIDI THRU   AUDIO GND    POWER GND
		p2  shl	   p2   shl   p2    shl   
-------------------------------------------------------------------------
ROLAND MKS20	O    O     -    -     Ch     Ch     yes:CH        No	 
		
Casio CZ-1	O    O     Ch   Ch    Ch     Ch     ~100ohms:ch!   yes

Yam. FB01	O    CH!    Ch   Ch    Ch     Ch     yes:Ch        no
		     
Yam. Qx5	O    CH!   Ch   Ch    Ch     Ch     -   -         no

Looks like Yamaha Shell connects to ground, so if you use a cable
whos sheild is connected to pin 2, you form a ground loop with
the Midi out or thru it connects to.

Now, whats this all mean? Well, midi still works, but
    you probably get more noise and hum in the audio. 
    
    How much is the question....    

    Uh, I never did understand ground loops.  I just know hum is bad
    and I unplug things until it goes away.  Then i use ground lifts
    to keep it away.  And I always wear rubber soled shoes, and make
    sure the floors are dry.
    
    But some hum comes from power supplies and can't be made to go away,
    at least not this way.
    
    Sorry Reg.
    
    len.
    

	I don't know if this is on the same subject or not, seein' as how
you all are mentioning hummmmmm as the product of improper grounding...

	But,

	Last weekend I went to pull a unit out of my rack, and upon touching the
rack screws - YEEOUCH!!  Holy Shack-wave, Batman!  I couldn't touch the screws, 
the rack brackets or any chassis without getting a real charge out of the
experience.  I had to power everything down to do what I set out to do.  I 
fiddled around a bit, but left frustrated.  I didn't know what was causing it.
	The next day, I went down to try out an idea I had for the drums and 
found no shock at all.  I'm trying real hard to remember if the day I felt the
charge was before I removed the RD200 to let someone borrow it.  I'm inclined to
think not.  I don't remember ever having that kind of problem before (although
I've had mikes arc to my lips in performances before...).

	Why was the shock there?  If nothing was changed, why would it be 
missing the next day?  If something HAD changed (i.e., removing the piano), 
what was wrong before?  Should I go through and (one by one) reverse prongs into
the power splitter until the problem disappears?

	Dan

    Get out a volt-ohmmeter, and measure the resistance between the outside
    case (metal screws are fine) and each 110VAC prong (with the power
    switch ON but the device unplugged and removed from the rack). 
    
    For the two flat prongs: Anything that shows worse than 50Kohms
    resistance is capable of killing you.  Anything showing less than a
    megohm is capable of giving a feelable "tingle"  (I know, your music
    makes you tingle all over _already_ :-)  ). 
                                               
    For the third (rounded, "ground") prong (if the device has one).
    This should show a direct short to the case; something like an ohm
    or less. If it doesn't, that's not good but it's also not bad; the
    device might have an interior case (grounded) and a floating outside
    case (very rare...).  Worth checking out (call the manufacturer
    and ask!)
    
    Get anything failing the above tests repaired before you plug it
    in again.  (or at least post something here so someone else with
    the same piece of equipment can check theirs and either verify that
    it's supposed to be that way or tell you your hardware is genuinely
    broken. )
    
    I personally don't trust ANYTHING that depends on a polarized plug
    in order to have a non-hot case.  Then again, I only own one piece
    of equipment that isn't wall-bug powered....

RE < Note 776.5 by CTHULU::YERAZUNIS "Hiding from the Turing Police" >

	By 'worse than 50Kohms', I take it you mean 'less than 50Kohms', right?
I'm not too shmart in dese tings, you know.

	Thanks for the help.

	Dan
                                               

    NO NO NO NO !
    
    The environment (that is, the world, sinks, telephones, pipes, wet
    floors, etc) contain a multitude of paths to ground.  If he happens
    to touch his rack (or anything "grounded" to it) and one of the
    above real grounds, he'll be strummin' with the angels!
    	
    The ONLY safe way is to fix whatever's making his rack electrically
    hot.
    
    (and yes, "very bad" means less than 50,000 ohms,
    	      "bad" means less than a meg or so.
    
    Watch out, as components deteriorate a 500,000 ohm reading may
    deteriorate to a 50,000 ohm reading.  Sharp knocks and jostles can
    also do it...
    	
    Makes you really wanna kiss the mike, eh?
    

	Just to clear up any misunderstandings...

	The rack is wooden, and the rack bracket for the sound units have no
contact through the rack box itself to the power splitter (which is in the back 
of the rack).

	Dan

    
    You have to go through the whole system and make sure that:
    
    the black wire is hot
    the white wire is neutral
    all grounds are continuous to the chassis
    
    It doesn't matter if the internal electronics are floating, that's
    common in a lot of circuit designs. As long as the chassis is grounded
    through both the neutral lead and the third prong.
    
    The most common situation I've run across is when someone buys a
    used piece of equipment (Dan, ya listening?) that some non-electrical
    type has put a new power cord onto. They reverse the black and white
    leads by accident, and they don't care 'cause it works'. Open the
    case and check it for yourself.
    
    Also, it takes a pretty good conduction path from your body to ground
    for someone to die from electrical shock. However, if your studio
    is in the basement on a cold, damp concrete floor (Dan, still there?)
    and you're in bare feet.....you are taking a BIG RISK. Wear sneakers.
    Carpet your studio, even with an old crapped out rug. I've been
    working with electricity for a lot of years now, and it still scares
    the living hell out of me. I take all the precautions I possibly
    can.
    
    CdH
    
    

	Well, just before coming in today I did the quick test of continuity
from case to all the plugs in the power splitter.  No problems there.  In fact,
the problem hasn't reoccured at all since that time last weekend.  I haven't yet
gone in to check all the power connections in each instrument.

	Dan

    Not that I'm an expert or anything, but isn't your studio in your
    basement?  And isn't your basement floor concrete?  And isn't your
    basement damp sometimes?

    Try wearing DRY rubber soled shoes.  I have yet to see a piece of
    equipment that won't unleash some type of undesirable electrical charge
    to the quickest ground path that exists.

    We used to get a kick out of this in our old band (rehearsed in our
    drummer's basement).  The bass player always wore penny loafers and
    spit a lot when he sang.  We'd always make sure he wasn't standing on
    the carpet and that he didn't have a wind screen.  You simply would not
    believe the pyrotechnics - or the chapped lips.

&*}

RE Chris and Brad...

	For the record, my basement is quite dry.  Only in the absolute wettest
of seasons have I had any problem with damp floors.

	Dan

    So, the ground-loop is gone, and all the equipment checks out to
    have sufficient isolation.	
    
    Hmmmm....
    
    Intermittent fault?
    
    Maybe you ought to get a GFI extension cord and use that from now
    on (cost about $20)
    	
    We'd hate to lose you...
    	
    	-Bill
    

RE < Note 776.14 by CTHULU::YERAZUNIS "Hiding from the Turing Police" >

>    Maybe you ought to get a GFI extension cord and use that from now
>    on (cost about $20)
    	
	Whazat?    

    GFI = Ground Fault Interrupter.  This a gadget that senses "bad"
    current flow to ground and opens the circuit, presumably before
    you get electrocuted.  You see them in modern bathrooms - they're
    the outlets with the little "push to test" buttons.
    
    len.
    

    >"push to test" buttons.
    
    Uh, what happens if it *fails* the test?
    
    Edd

	I was just thinking about the nature of the replies and had a thought.
You know, none of the units in the offending rack have three prong plugs.  
Therefore, it would seem to this puny mind that ground (at least from the AC
side of things) has nothing to do with it.  Am I missing something?

	Dan

    GFI: Ground Fault Interruptor:  A little box that counts electrons
    going OUT to your rack, and electrons coming back IN from the rack.
    If the counts match, no problem.  If either more go out than come
    back, or more come back than were sent out, WHAMO, it disconnects
    BOTH wires internally. (you reset it by pushing the second button
    back in).  The GFI reacts much faster than your heart does to the
    shock event; hopefully fast enough that you feel a mild jolt and
    hear the WHAM of the GFI breaker tripping, but your heart continues
    to beat. (40 milliseconds is the max. delay time allowed for a GFI to
    be UL rated)
    
    
    Why this is good: MOST (not all) user-zap effects are caused by
    a user bridging his (her) body between one of the two power lines
    and an external ground (damp floor, water pipe, etc).  This causes
    an imbalance in the IN/OUT electron count, which is what the GFI
    triggers on.                                          
    
    The type you want is built into the end of a 12-foot heavy duty
    extension cord (outdoor armored, even resists beer). Channel 
    Hardware has them. 
    
    _Go_Get_One_ ...  _Now_!
    
    --------------------------------------------
    
    Lack of a third prong has nothing to do with your problem; you've
    got an intermittent short of hot to chassis and the third prong
    won't eliminate the hummm (though it MIGHT _but_not_for_sure_ cause 
    the fuse to blow the next time that intermittent crops up.)
    

RE < Note 776.19 by CTHULU::YERAZUNIS "Hiding from the Turing Police" >

	Browsing through the NEWARK catalog I see GFI units (though not
part of extension cords) going for upwards of $50.  Is that what you're
refering to?

	BTW, where's Channel Hardware?

	Dan

    Channel Hardware, in Framingham, Massachusetts, USA.
    
    Right across the hall in the same mall as Newbury Comics (of CDNOTES
    fame).
    
    $50 is what you might have to pay for a fuse-box mounted GFI/breaker
    combination.  The GFI that protects my bathroom cost me $19 (and
    fits in a regular outlet box).
    
    The extension cord units are comparible in price.  Where are you?
    	
    	-Bill
    

    re: .21 and $19 GFCI's
    
    Even THAT's too much.  On sale, you can get them for about $9.50
    these days.
    
    Just open up your power strip, put in in as the first outlets and
    everything that goes through it will be protected as well.  Throw 3 110
    VAC MOV's on the line before it and you're protected from just about
    everything nature can throw at you. Good stuff cheap. 
    
    -joet

    > put in in as the first outlets 
    
    ...except most GFI's are square-format outlets and most power strips
    are the double-oval format.
    
    You'll need a bit of hacksawing, but that's not that hard...
    
    and it WILL work.  Nice idea, actually.  Maybe I should mung my
    power strip to be that way...
    
    	-Bill
    	 

RE < Note 776.22 by JOET::JOET "Deatht�ngue lives!" >

>    Throw 3 110
>    VAC MOV's on the line before it and you're protected from just about
>    everything nature can throw at you. Good stuff cheap. 
    
	Wazzat?

    
    Re: .22,.24
    
    MOV = Metal Oxide Varistor
    
    Sort of like two diodes back to back, wire between hot and ground,
    any voltage surges get shunted to ground.  This is what you'll find
    inside most cheap "surge protector" outlet strips.
    
    

    re: .24, .25
    
    Actually, you wire them between each pair of wires in your strip (hot
    to ground, hot to neutral, and neutral to ground) and they'll catch any
    spikes coming down the line.  Radio Schlock has 'em, just make sure you
    get the 110 volt and not not the 5 volt variety. 
    
    re: .23 (I think?)
    
    You really should make up your own power strips.  That way, you can
    fuse 'em, switch 'em, light 'em, GFCI 'em or whatever else you like
    (leaving out what you DON'T like) and you know that they're made
    of quality components.  They might weigh a ton, but they'll outlast
    the K-Mart variety by years.                    
    
    -joet

    where did the original problem go?
    
    so the GFI trips when the symtoms occur again....
    
    you havent fixed it....youve designed a sensor to 
    tell you when the problem occurs!
    
    (Did you BTW happen to have a polarized plug in backwards
     because you defeated it with an extension cord or something?)
    
    ron
    

    Well, the simple problem is that it's an intermittent; he can't
    find it if it never crops up again and it'll fry him if it does.
    

RE < Note 776.27 by JON::ROSS "shiver me timbres...." >

>    where did the original problem go?

	I'd like to know that meself...
    
>    (Did you BTW happen to have a polarized plug in backwards
>     because you defeated it with an extension cord or something?)

	There may well be a cross-polarization (is that a good way to say it?)
as all the units are simple two-pronged power plugs (with the possible exception
of the TZ - still haven't checked).  I do not recall having to force any plugs,
which means the plugs and/or power strip may not be set up for polarized 
connections.
    
	Dan    

    
    If you have an intermittent short of AC hot to the case, there should
    be arcing going on inside the case and you should be blowing fuses.
    If a power cord is wired backwards everything would work but you
    might get zapped if you touched the right two cases.
    
    Either way, the best thing to do is to pull all items out of the
    rack, open the top of the case and take a peek around where the
    line cord enters. You might have a pinched cord at the strain relief
    that is shorting hot to the case. The line cord, fuse holder or
    circuit breaker may be loose and the black wire may be touching
    the chassis. At any rate, make sure the black wire (hot) is the
    one connected to the fuse or breaker. If it's white it's wired
    backwards according to the NEC.
    
    GFI outlets may be great for when you're playing out but are just a
    band-aid for Dan. He should really trace his problem down and fix
    it. I don't use GFI's because if by any chance they do trip, they'll
    cut out the rack power which will send a nasty spike down to the
    amp inputs, which might blow your speakers. 
    
    CdH
    

    Better to lose rack power and possibly a speaker driver than to
    require the services of a mortician...
    
    ------------------------------
    
    > If you have an intermittent short of AC hot to the case, there should
    > be arcing going on inside the case and you should be blowing fuses.
    > If a power cord is wired backwards everything would work but you
    > might get zapped if you touched the right two cases.           
    
    I don't think so... he's stated that none of the equipment has a
    3-prong plug, hence it will NOT blow a fuse if ONLY hot or neutral
    (with flipped polarization) is shorted to the case.
    
    In fact, your model of one device, with one intermittent short of
    one of the line leads to case, fits the observed behavior perfectly;
    
    	- It never happened before (neutral intermittent shorted to case)
        - It was pretty bad 
    		(luck of draw, plug flipped, now hot was shorted to case)
    	- It's gone now and hasn't been reproduceable
    		(plug is flipped again, neutral intermittent shorted
    		 to case, so it's not greatly noticeable)
    
    We also know that his power strip is grounded, so hot and neutral
    on the powerstrip are "correct" (provided the outlet was wired
    correctly, not always a valid assumption) 
                                  

    People have been talking here about the possiblity of fatal shocks.
    I've gotten some very nasty shocks before ranging from the old finger
    in the light socket when I was a kid (I just didn't believe mom) to a
    400V+ shock from the filter caps on an old Fender deluxe amp. The worst
    injury was a bit of light-headedness and a very deep burn on my finger
    tip from the Fender. Is death *really* a possibility here. I always
    thought that you'd need alot more power to kill a person. I've only
    heard of a few case where people have been kill by electric shock from
    amps and such.
    
    pcv

    
    Re: .31
    
    If it's a two wire plug and white is grounded to the case, then a
    short between hot and the case would at least arc and might blow
    fuses, no?
    
    Re: .32
    
    I can dig up some numbers somewhere in the NEC stuff I have at home
    but the point is, a concrete floored basement, bare feet, and ground
    problems CAN KILL. Every concrete basement is damp, concrete is
    >50% water. Otherwise it would be a pile of mortar dust, like how
    it started. 
    
    CdH
    

RE < Note 776.31 by CTHULU::YERAZUNIS "Hiding from the Turing Police" >

	A lot of this goes over my head.  But I did want to make one point...

>    I don't think so... he's stated that none of the equipment has a
>    3-prong plug, hence it will NOT blow a fuse if ONLY hot or neutral
>    (with flipped polarization) is shorted to the case.

	I haven't yet verified whether ALL the equipment has no 3-prongs.  I
know the Roland doesn't, I know the Korg doesn't, there's still the TZ and
(I was forgetting this one) the Kawai mixer.
    
	As far as how sever the shock was, well, I don't know what to say here.
Not being a lover of pain, I may have exxagerated.  I usually test 9-volt
batteries by touching both prongs to my tongu, but that's about as far as I'll
go.  I WAS able to repeat touching the offending hardware, though not for more 
than a second.  It didn't feel dangerous, just not advisable.

>    We also know that his power strip is grounded, so hot and neutral
>    on the powerstrip are "correct" (provided the outlet was wired
>    correctly, not always a valid assumption) 

	I can't say whether the system was properly grounded.  It used three 
prong plugs, sure, but where the wall plug takes that ground - I have no idea.

	Dan

    Under perfect conditions (grazing contact, dry skin, healthy body,
    circuit avoids current through thorax), a 110VAC shock is rarely fatal. 
                                                       
    However, if any of the above are untrue it is perfectly possible
    to go into cardiac arrest on a 110VAC shock.
    
    1) Clenching contact instead of grazing contact.  In a grazing contact
    the muscle jerk tends to pull you away from the charged surface.
    In a clenching contact, the muscle jerk pulls you tighter to the
    charged surface- which further increases the current, which increases
    the muscle jerk.  How do you hold the microphone?
                                                          
    2) Damp skin.  Most of the insulating value of dry skin is in the
    porous top few layers of dead cells.  When dry, they insulate. Moisture
    in the pores negates this insulation. Note that perspiration is salt
    water- which conducts electricity VERY well.  Do you perspire when
    you perform?  :-) 
                                                          
    3) Overall health of victim.  'Nuff said.
    
    4) Does the current pass directly in the region of the heart and
    diaphragm, or through the brain?  Bridging a 110VAC line with two
    fingers of the same hand will hurt, but not much.  Bridging them
    with two fingers on OPPOSITE hands will route the current through
    the chest area, possibly causing cardiac arrest.  Current through
    the brain will cause convulsions and loss of the memory of
    the few minutes directly preceding the shock (erasure of short-term
    memory).  
    
    This is the reason for the electricians "one hand in your back pocket"
    rule; if you're wearing insulating boots, and avoid all other
    connections to ground (like having one hand in your pocket instead
    of on the fusebox case) then any current will tend to stay out at
    your hand and not go through your chest.
              
    -------------------------------------
    
    Other interesting facts:
                                                                 
    The most dangerous currents are those in the range of 4 to 20
    milliamperes (through chest).  At less than 4 (or so) the heart can
    continue to beat, at greater than 20, the heart siezes in a contracted
    state but when the current is removed, normal heartbeat usually
    returns.  In the 4-20 mA range, the heart does not stop, but begins to
    fibrillate (uncoordinated contractions of heart muscle). A fibrillating
    heart is ineffective as a pump, and since the fibrillation often
    continues even when the current is removed, the victim needs immediate
    CPR or defibrillation. 
                                                        
    At high voltages (440 V or more) the skin is ineffective as an
    insulator because it quickly heats, chars, and flakes away, leaving
    a low-resistance path through the muscle and circulatory system
    for current to pass.  Hence, even a grazing contact at 440+V is likely
    to kill.                                                   

    I can think of several things that might have saved you on the Fender
    amp incident:
    	
    - the filter caps discharged through you, but the recharge circuit
    couldn't keep up with the drain you were making;
    
    - the circuit didn't go through your chest;
    
    - the muscle twitch pulled you away from the contact;
    
    
    You're actually a very lucky person.  HV can kill. 
    
    I bet it hurt like ****, too.  

    RE: making your own GFI power strip
    
    Wouldn't it be easier to plug an off the shelf strip into a single GFI?
    Would this work the same?
    
    Tim
     

    Yes, it would.
    

Looks like those wall-bug power supplies are a good idea after all.

    re:.36
    
    2 out of 3.
    
    I wasn't following the one handed approach, so the circuit went right
    up one arm across my chest and through my other arm. As far as muscle
    twitch is concerned, I'd say a more appropriate term would be "muscle
    knock out of chair" Not only did it hurt like ****, it scared the ****
    out of me. I remember the rest of the band was in the other room
    practicing, and saw me fall out of my chair. At first they thought I
    was kidding, till I showed them my finger with a burn spot on it.
    
    Just think, you guys may save a life yet. Thanks for the info, I'll be
    more careful from now on.
    
    pcv

    Luck us, here in the USA. In Europe, where they run 220 volts, a
    few people are killed each year, as they arc-weld thier lips to
    a microphone. I have a freind in Stockholm Sweden who has been hurt
    badly by this in the past. I guess, thou, we can't all use batteries.
    
    							Jens

    I got hammered by a CRT anode once (I believe that's around 10kV).
    
    I was following the "one-hand rule" (CRT's, even then, scared the ****
    out of me), and I was wearing rubber shoes on carpet at the time. The
    tube must have been mostly discharged as well. 
    
    Basically, I didn't even touch the anode: it arced right to my
    finger... 
    
    I didn't get burned, but I did jump a few feet, and my finger felt
    like I hit it with a hammer for the rest of the day...
    				- HBM

    
    re .42
    
    	I wouldn't know, I've never hit a finger of mine with a hammer
    for the rest of the day.

Nothing like bringing an old topic back to life :-)

I just went through this note and read all the replies.  I found it very
interesting to read 1000 ways to fry yourself.  I am going to soon go home
and check all my stuff out to make sure everything is cool in the hook-ups
(and to eliminate the hum!).

My question is related to voltage and dying.  One time at the science museum
there was some sort of presentation about electricity and so forth.

They had to big tesla coils there, both at very high voltages.  One of them
had a pointy tip and a real lot of little arcs going into it.  The demonstrator
explained that the frequency of this was some real big number (I forget,
this was years ago) and that although one would be shocked, one
wouldn't be killed by coming into contact with the electrical arcs.  The other
one had a round ball tip (maybe I am reversing the two ?) and a few big
arcs going into it.  He explained that the frequency of this was about 60hz
or so and was very deadly.  He said that what kills people who come into
contact with exposed plugs etc was that the frequency was low enough
that the heart tried to match it, ie, beat at 60hz and this is what caused
the cardiac arrests.  He went on to say that at a real high frequency,
it was too fast for the heart to react too so that it didn't try to match
10000hz or so.  Of course, he did mention that the high voltages can cause
great damage to your body (ie, don't do this at home kiddies :-)

I bringthis up because it sems at odds with what I've read hear and I am
wondering about it.  Bill?

Chad

    When you walk across a rug on a dry day you can generate many thousands
    of volts in static electricity, but almost no current. You need
    high voltage to ionize the air into conducting electricity. This
    is what you see when you see an electrical arc, ionized air.
    
    	The culprit in most electrocutions is CURRENT. Too much electrical
    current through the body can disrupt biological processes in an
    undesireable way. Have you ever noticed what happens to two pieces
    of metal that had been shorted together with a large current present?
    Usually one will be pitted. This is caused by large amounts of current.
    
    	Frequency can cause problems even if the amount of current would
    not normally be dangerous. You had the right idea in that the heart
    gets confused by the charge coming in. If the frequency is too close
    to the normal "messages" from the brain the heart could go into
    fibrilation (sp?). This is when the different areas of the heart
    begin to contract and expand all out of sync with each other. Result:
    a lot of work done, but very little circulation to the body.
    
    	Some new medical techniques for disolving gaul stones and kidney
    stones use ultrasonic shock waves. The patients heart is monitored
    to avoid causing fibrilation. Apparently there is one key phase
    in the cycle of the heart beat where the heart is vulnerable to
    disruption. Monitoring the heart allows the equipment to avoid this
    phase.
    
    					Mark
    

    I am uncertain, since body tissue is inhomogeneous, but sufficiently
    high frequencies may display skin effect and not penetrate the body.
    Tom

< Note 776.44 by NORGE::CHAD "Ich glaube Ich t�te Ich h�tte" >
                                -< a question
 >-

Chad,

It's not really a matter of frequency. It gets back to good old Ohm's law.
It's the current that can kill. I've been shocked by 30KV from a tv set,
and aside from a painful arm, suffered no other physical damage. Mentally...
well...

Anyway, since it is   current = voltage / resistance, the amount of current
will depend on your body resistance and whether or not you are playing around
with batteries (say a 12v car battery), line voltage (110-120 vac rms), or
high voltage such as a tv set picture tube. If you take a VOM and set the
resistance to measure around the 100Kohm range, hold one probe tip between
index finger and thumb in each hand, you will see that your body resistance
"hand to hand" is approx 100k ohm. This reading will vary with how tightly
you hold the probes because of surface area, contact resistance, moisture,
etc. I was trained as a technician in the 60's, to keep one hand in a pocket
or behind my back when probing high voltage areas. This is because if you get
one hand on earth ground or electrical (chassis) ground, and the other hand
on high voltage, your body has completed the electrical circuit, and the
current passes thru one arm, thru your chest (and heart tissue) and down
the other arm. The same thing applies to having your feet be grounded and
touching high voltage with a hand, although the body resistance from a hand
to a foot is somewhat greater. The thing that kills is the current.
Approximately 10-20 milliamps is required to kill, and it must be sustained
for a period of seconds if your heart is healthy. It paralyzes your muscles,
interrupts the nervous system involuntary muscle signals from the brain which
regulate your pulse, and that is what stops your heart. Doctors can also
restart your heart beating again by using a CVRM
(Cardio-Vascular Resuscitation Machine) which uses a high
voltage spike to cause the heart muscle to contract suddenly. The hope here is
that this will stimulate the heart to beat rhythmically again. This voltage
spike is very short so that it does not paralyze the heart and diaphragm
muscles. They use conductive disks connected to high voltage insulated probes.
They use a silicon grease paste on the disks to reduce body skin resistance.
It is important that none of the other people in the area touch the
patient when using the CVRM, because the same electrical spike could cause
irregular heart beat, ventricular fibrillation, and finally heart stoppage to
a normal person. 

dave

    Its the volts that jolt but the mils that kills!! (mils=milliamps).
    
    Ken