[LAU] Terrible mic ground noise

[Gene Heskett]

On Monday 01 April 2013 19:37:44 jonetsu at teksavvy.com did opine:

> Le 01-04-2013 09:58, Gene Heskett a أ©critآ :
> > THE IMPORTANT PART of this msg:
> > 
> > At the lumberyards, like Lowes or Home Depot, in the electrical
> > aisle, they
> > have shirt pocket sized electrical 'Sniffers" not much bigger than a
> > pen or
> > pencil.  Often their power switch is the pocket clip, you grab the
> > end and
> > squeeze the clip shut, then the other end has a plastic coated blade,
> > and
> > it will trill like a canary & blink an LED you can see when that
> > blade is
> > within 1 to 2 inches of a live wire.
> > 
> > They sell for something in the ten dollar range, very cheap for
> > something
> > that can save your life by finding hot stuff that isn't supposed to
> > be,
> > like your refrigerator, often installed within reach of the usually
> > well
> > grounded stuff of the kitchen sink?
> 
> The reply was an entertaining read !
> 
> Now if I understood the above correctly, a hot device would be one from
> which someone would get a shock by touching it, is it ?
 
That depends to a surprising extent on the surroundings.  If everything is 
hot, then so are you by capacitative coupling from the environment, so a 
shock is not real likely because the currant would have no place to go.  
OTOH, if standing on a metal railing that is grounded, and bare foot too, 
then touching anything electric without first probing it with one of these 
sniffers could be the last thing you touch.

I have found also that even if the metal surfaces are well painted, you can 
often detect a hot item by touching it very gently with the back of your 
hand and sliding along it with the touch.  A hot item will feel faintly as 
if its vibrating, whereas the properly grounded item will have no vibration 
as the back of the hand is brushed across it.

HOWEVER, if there is even a remote possibility of more than the std 127 
volts of AC in the area, I don't recommend it.  If the paint has a pinhole, 
you can get a quite nasty buzz.  In this regard, DC is the much more 
dangerous situation as you probably won't feel it until it has a good grip 
on you.

IOW, get the sniffer AND learn how to use it, although that part isn't at 
all difficult.  I don't care if you're flipping burgers at Mac's for 
minimum wage, it could save your life.

Something else to consider is that there is a lethal "window" to the 
currant passing directly through the heart.  It can develop a rhythm loss 
and go into fibrillation at currants above 20 micro amperes, a lethal 
situation because its just sitting there shaking without moving enough 
blood to sustain life.  You have maybe 1 long minute to get that fixed else 
brain damage is bound to occur.  This can happen at currants so low you may 
not even feel the shock.  And the defib machine paddles will be needed a 
very large percentage of the time as its a condition that isn't self 
fixing.  The shock from the defib paddles works by momentarily freezing the 
heart, and when it next beats it will beat in unison with itself.  Most of 
the time...  If not, the techs will let it charge again, and slap you 2x 
harder, wash, rinse & repeat until you are either running, or the machine 
has hit you with its max jolt quite a few times.

Going up in currant, at currants above 20 milliamperes the heart just 
freezes.  There, you have that same long minute to remove the shock before 
brain damage will set in, but when the currant is removed, the heart 
usually starts right back up and goes about its business as if nothing 
happened.  Typically the major after effects of that will be caring for the 
2nd degree burns it causes, and often, because your immune system has been 
knocked around pretty badly, a few days later a session of the shingles 
will set in for about a 2 month visit.  BTDT, ain't no way in hell you 
could call _that_ fun.

This sniffer I preach about doesn't work well for high voltage DC, beeping 
once or twice as its brought near, and one or 2 times as its pulled away.  
The characteristic coaches whistle trill they do is because the AC field is 
turning it on and off at 50 or 60 hertz.  But high voltage DC isn't 
normally a worry for the general public except around high power broadcast 
transmitters, some of which use over 20,000 volts.

And TBT, I don't often write this stuff for its entertainment value, it is 
supposed to be educational.  If I throw in a little humor, its as much to 
keep you reading as for the humor in it.

Cheers, Gene
-- 
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