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Old 05-17-2006, 09:02 PM   #1
PeteS in CA
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Default Hazardous-voltage primer

Hazardous-voltage primer
Understanding the hazards associated with voltage and knowing the principles
of safety and the importance of certification are the keys to safe design
and product use. Even low voltage is hazardous and can damage products and
harm users.
By David Lohbeck, National Instruments -- EDN, 5/11/2006
Quote:
It is common knowledge that wall-outlet voltages of 120V in the
United States and 230V in Europe can cause severe shock or death, but did
you know that many people consider 120 and 230V to be low-voltage? Believe
it or not, according to most standards, voltages less than or equal to 1000V
are low. Voltages greater than 1000V are high and are not commonplace in the
typical home or workplace. More specifically, peak voltage greater than
42.4V is hazardous; voltage less than or equal to 42.4V, or SELV (safety
extra-low voltage), is nonhazardous. It is difficult to know when
electricity can cause serious injury or be fatal.
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Old 05-18-2006, 12:11 AM   #2
arneson
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Default Re: Hazardous-voltage primer

It's amazing were still alive.
Warning stickers are good.
Monitors are notorius for zapping people.
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Old 05-18-2006, 01:54 AM   #3
kc8adu
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Default Re: Hazardous-voltage primer

Quote:
Originally Posted by arneson
It's amazing were still alive.
Warning stickers are good.
Monitors are notorius for zapping people.
monitors are far from the most dangerous item in a normal home.
watch out for the nuker!
transformer secondary up to 4000vac.
a guy i fix stuff for told a relative in ky to stay out of the works of one and wait till it could be brought up here to me.would not listen and now qualifies for a darwin award.
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Old 05-18-2006, 02:28 AM   #4
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Default Re: Hazardous-voltage primer

Fluke 1AC-E Voltalert and 1000v insulated screwdriver



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File Type: jpg volt.jpg (50.1 KB, 84 views)
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Old 05-18-2006, 07:15 AM   #5
tiresias
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Default Re: Hazardous-voltage primer

As important as the voltage/current involved is the nature of the current:

From Basic Res. Cardiol. 78, 604-616 (1983): graph showing fibrillation threshold in mA vs. frequency of sinusoidal AC:




Note how the most lethal AC frequency is around 30Hz, although as you can see 50-60Hz isn't much safer. This experiment was carried out on isolated heart tissue - in "real life" the highest AC frequencies are even less likely to cause VF due to their reduced degree of penetration into the body.


....

PS. If any of you are interested, let me know and I can forward you the "full text" of the experiment.
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Last edited by tiresias; 05-18-2006 at 07:22 AM..
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Old 05-30-2006, 09:48 PM   #6
Rubycon
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Default Re: Hazardous-voltage primer

I can tell you from experience first hand that the ring voltage on a telephone line is quite painful - when the wire is in your mouth.

The microwave is definitely lethal with 2kV at 500mA most common. Neon sign transformers at 15kV and 60mA are extremely dangerous. Put some caps across the output and the arcing is deafening. Ask any tesla coiler that's used a pole pig in reverse - stepping up 240v "house power" to 13kV or higher - often at currents over 1 AMP! Makes the lights dim in the neighborhood. Touch that and you'll be riding in a Caddie for a dirtnap.
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Old 05-30-2006, 10:31 PM   #7
arneson
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Default Re: Hazardous-voltage primer

Air conditioners have nailed me a couple of times.
Those are big caps and compressors are high current.
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