[AMPS] volts, Hertz

George T. Daughters gdaught6@leland.Stanford.EDU
Mon, 6 Oct 1997 09:17:54 +0008


peter quoted rich, 

> >IMO, the electric-mains is a greater danger.  With HV, the careless
> idiot often gets blown clear.  With 120v/240v, he typically can not let go.  
> >Next stop, "Silent Keys" in *QST*.  

and added,
> It is claimed in many places that the most dangerous voltages are
> between 400 and 1600 DC, as that usually leads to ventricular
> fibrillation. Some people claimed  that sweep tube linears were safer
> because the voltages were lower - another myth! 
> But having had a number of bad shocks in the past, I suggest being VERY
> careful. It's surprisng, as Rich says, how many people get blown clear -
> it happens on the 25KV overhead electric lines used here for the railway
> - about 10% get blown clear, while very few survive the 750volt DC used
> on the third rail systems here. That's not enough to rely on it, though.

my nickel's worth is that it also depends on whether it's ac or dc.  
medical research has shown that the most lethal shock (i.e. lowest 
current necessary to cause death) is ac in the vicinity of 50 or 60 
Hz... the choice of our power providers!  (i know there are good 
reasons for this choice, too)  so treat the mains with a great deal 
of respect! (even though they are "low" voltage compared to tube 
plate voltages, for example)  but a nice-well filtered dc hv power 
supply will make you *just as dead!*

the basic rules i follow (i claim no originality here)

1.  turn it off
2. unplug it
3. short it with a low value resistor, then with a wire (that's any 
and all points in the circuit where electrical energy can be stored.)
4. work on it.

if you *must* work on it "alive," apply the "1 hand in a pocket" 
rule.  (work on it with one hand only.  the other hand is in a 
pocket.  this way you don't provide a path across your thorax, where 
your heart resides.)

73,  stay safe!
George T. Daughters, K6GT

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