Author Topic: How much to feel something?  (Read 6620 times)

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Offline FlashedBIOS

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How much to feel something?
« on: March 20, 2015, 02:24:47 am »
I was watching an episode of Halt and Catch Fire.  In one part Joe and cameron are in the test lab and joe turns on a bench power supply and grabs the terminals and turns the voltage up, but you dont get to see how much.  then he grabs camerons hand and cameron touches the ground terminal i think while joe touches the positive. I have a few questions

Is it dangerous?  Can DC voltage hurt you

how much voltage / amperage would it take to cross two people and have them feel something

and how high the voltage before it hurts you?
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Re: How much to feel something?
« Reply #1 on: March 20, 2015, 02:32:24 am »
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Offline c4757p

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Re: How much to feel something?
« Reply #2 on: March 20, 2015, 02:32:53 am »
Yes, DC can hurt you. How much depends on the phase of the moon and the price of tea in China - as low as 30V if you're a really unlucky bastard, but then, I've touched 600V (not on purpose!) and I'm not talking to you from the Great Beyond...

There are a lot of threads on this here. Have a look around.
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Offline Simon

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Re: How much to feel something?
« Reply #3 on: March 20, 2015, 02:34:11 am »
A friend and fellow forum member was telling me just yesterday that he put a supply up to 70V before he felt anything. Problem is that it's highly subjective and with DC it's harder to let go.

Basically don't try it yourself.
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Offline JohnnyBerg

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Re: How much to feel something?
« Reply #4 on: March 20, 2015, 02:35:04 am »
Is it dangerous?  Can DC voltage hurt you

Yes and Yes

Quote
how much voltage / amperage would it take to cross two people and have them feel something

It is the current that is dangerous. A current of 60mA can disturb a human hart beat, or even stop the hart.


Quote
and how high the voltage before it hurts you?

Ohms law!
If you wear rubber boots you need a much higher voltage to reach a certain current from arm to floor compared to putting the electrodes on your tongue.
 

Offline Simon

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Re: How much to feel something?
« Reply #5 on: March 20, 2015, 02:55:35 am »
I think the question was arm to arm not to floor. 30mA is considered very dangerous even that is what RCD's trip at although they will trip slower at lower currents.
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Offline FlashedBIOS

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Re: How much to feel something?
« Reply #6 on: March 20, 2015, 03:19:30 am »
wow.  under 1 amp can hurt you?  that means a USB port can hurt you!  wow.
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Offline JohnnyBerg

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Re: How much to feel something?
« Reply #7 on: March 20, 2015, 03:30:49 am »
wow.  under 1 amp can hurt you?  that means a USB port can hurt you!  wow.

Always think with ohms law.

If you have a multimeter, set it on Resistance 200K and grap the leads. What resistance do you measure?
USB is 5V, how much current will flow when you grap a usb connector?

Now, still in 200K position, put the leads on your tongue. What resistance do you measure?
What would happen if you put a USB connector on you tongue?
 

Offline Simon

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Re: How much to feel something?
« Reply #8 on: March 20, 2015, 03:32:39 am »
wow.  under 1 amp can hurt you?  that means a USB port can hurt you!  wow.

No  :palm: Ohms law! you need enough voltage to drive that current through your body, your body is a resistor, typically assumed to be 1000 ohms but it will vary, so at 240V that is 240mA so you need the RCD to blow very very fast it needs at least 30VAC to drive the 30mA through you. over 50V is as standard considered dangerous
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Offline IanB

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Re: How much to feel something?
« Reply #9 on: March 20, 2015, 03:58:40 am »
I have been able to feel a tingle in my fingers from 15 V AC.

A 9 V battery across the tongue is very stimulating  :)

Last time I tested 120 V AC across my fingers it caused me to use some interesting language  :o

So what you can feel is very subjective and varies with conditions, especially how damp your fingers are.

I would not want to accidentally touch power supplies set above 50 V, AC or DC. It is best not to deliberately touch any power supply. Just in case things are not what they seem.
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Online Rerouter

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Re: How much to feel something?
« Reply #10 on: March 20, 2015, 04:36:02 am »
at least in Aus, about 50V AC, or above 70V DC is where the line in the sand has been drawn saying this is potentially life threatening and you need an electrical or disconnect-reconnect license to continue.

measure the resistance between your thumbs at random points in the day and you will see it change quite varyingly, i myself tend to lie somewhere within 10K and 370K depending on the day of the week, from this divide the voltage by the resistance (in ohms) and if you exceed 6mA, your in potentially life threatening territory, (6mA because your supply may be continuous)
 

Offline Simon

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Re: How much to feel something?
« Reply #11 on: March 20, 2015, 04:42:34 am »
(6mA because your supply may be continuous)

Precisely there are accepted amounts of current for accepted amounts if time that are deemed limits, so an RCD will trip at a certain speed for 6mA but it will trip a lot faster at 30mA, it's about how much the human body can withstand and for how long.
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Offline C222

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Re: How much to feel something?
« Reply #12 on: March 20, 2015, 05:06:14 am »
Surprised I haven't seen this linked yet:
 

Offline katzohki

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Re: How much to feel something?
« Reply #13 on: March 20, 2015, 05:29:21 am »
People say that current kills, but really in my opinion it's the combination of voltage and current (POWER) that kills. I've been shocked numerous times with up to 4000V, but I was fine because it's low power.

Surely 1A @ 1000V would kill, surely also 1000A @ 1V would kill as well. Of course, that's all just non-medical supposition. Let me know if you want to volunteer to try it.
 

Offline Simon

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Re: How much to feel something?
« Reply #14 on: March 20, 2015, 05:32:27 am »
but to get 1000A through your body you need 1MegaV for AC and I hate to think how much DC, it's actually about the amount of current at WHATEVER voltage is required to drive it. If 50V drove enough current to kill you (30mA) how will it be the same "power" if someone else needs 100V to drive the same current. It's your body resistance that counts
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Offline JohnnyBerg

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Re: How much to feel something?
« Reply #15 on: March 20, 2015, 05:35:40 am »
People say that current kills, but really in my opinion it's the combination of voltage and current (POWER) that kills.

The combination of voltage and current is called Ohms law.  :-DD

Quote
surely also 1000A @ 1V would kill as well

..

Let me know if you want to volunteer to try it.

I'll volunteer for the 1000A @ 1V. Just let me know how to set up the gear, and Ill hook myself on to it!
 

Offline Simon

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Re: How much to feel something?
« Reply #16 on: March 20, 2015, 05:37:07 am »
just look up photonic induction on youtube, he shows that 1V 1000A does not kill, how do you think welding is done without killing people ?
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Offline katzohki

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Re: How much to feel something?
« Reply #17 on: March 20, 2015, 06:17:24 am »
I've seen some of his videos, I'll have to check it out. For one thing welding current isn't designed to go through a person.

Maybe I'm wrong, like I said it's just my interpretation based not at all on any medical understanding.

@JohnnyBerg: Yes, Ohm's law. Pretty sure I've heard of that somewhere...

Thinking of the 1V @ 1000A, it's really more of a thought experiment, but if you treat the body as a simple resistor then yes, the required low resistance is off the scale according to this: http://epb.apogee.net/foe/fshrrh.asp.

I wonder if people with metallic implants have different effects from electric shock.
 

Offline JohnnyBerg

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Re: How much to feel something?
« Reply #18 on: March 20, 2015, 06:23:03 am »
@katzohki: just grap the leads of your multimeter when its on 20K resistance, and see how low you can get by sqeezing your fingers.

Then use Ohms law to calculate the current at 1V  :D
 

Offline amyk

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Re: How much to feel something?
« Reply #19 on: March 20, 2015, 09:11:53 am »
People say that current kills, but really in my opinion it's the combination of voltage and current (POWER) that kills. I've been shocked numerous times with up to 4000V, but I was fine because it's low power.
...don't forget time, which leads to energy being the crucial factor.

A perceptible shock from static electricity will be at least several kV if not higher, and the peak current/power thus very high, but the discharge doesn't last long enough to cause adverse effects.
 

Offline 691175002

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Re: How much to feel something?
« Reply #20 on: March 20, 2015, 10:24:22 am »
Whenever people are surprised about how little electricity it takes to kill I'm reminded of this guy:
http://www.darwinawards.com/darwin/darwin1999-50.html

He managed to kill himself with less than 10 volts.
 

Offline Evil Lurker

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Re: How much to feel something?
« Reply #21 on: March 20, 2015, 10:56:49 am »
It's all depends on a lot of variables... moisture/sweat on the skin, the size of the area of contact (next time you have a problem with static electricity and get shocked every time you touch something try using a solid metal key... you will see and hear the spark but not feel it), the part(s) of your body that make contact, frequency, so on and so forth.

Technically a 9V battery touched to the tongue will shock you for what it is worth but you can get bumped by the terminals on a welder and not feel a thing or just a little tingle (unless it is damp). 
 

Offline SL4P

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Re: How much to feel something?
« Reply #22 on: March 20, 2015, 11:09:10 am »
... shows that 1V 1000A does not kill

And if the same power (1000V @ 1A) is used, do you get the same result?
I don't think so!

This topic has been done to death - and a few unfortunates are no longer here to vent their overheated gas.
Read, learn, and consider the liability before someone takes your ill-informed advice.

If you're lucky - it will only be your hand or foot.
« Last Edit: March 20, 2015, 11:19:56 am by SL4P »
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Offline EEVblog

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Re: How much to feel something?
« Reply #23 on: March 20, 2015, 12:29:17 pm »
Over 50V DC starts putting you in the risky area:
http://en.wikipedia.org/wiki/High_voltage
Some meters have high voltage warnings at greater than about 38V or so IIRC.
The IEC standard of <120V is crazy high IMO!
 

Offline HackedFridgeMagnet

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Re: How much to feel something?
« Reply #24 on: March 20, 2015, 12:32:31 pm »
A static shock, something we have all had is a few thousand volts. And ouch it does hurt.
IC's dont seem to like it either.
 

Offline IanB

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Re: How much to feel something?
« Reply #25 on: March 20, 2015, 12:59:46 pm »
Over 50V DC starts putting you in the risky area:
http://en.wikipedia.org/wiki/High_voltage
Some meters have high voltage warnings at greater than about 38V or so IIRC.
The IEC standard of <120V is crazy high IMO!

If you got two sharp needles and stuck them through your rib cage into your heart and then applied 12 V across them it might kill you...everything is relative. The only safe voltage is no voltage  :-\
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