Killed By Volts

[Supermike]

On Bill Roach's Who Do You Think You Are an expert was saying that electrical voltage would kill you. I thought that amps played a big part in the current that would kill you as some people survived being struck by lightning. Am I wrong in this assumption?

[factor-fiction]

Yes - i think it's the current (measured in amps) that kills you. This requires a Potential Difference (the voltage) and a circuit. I remember V= IxR

[J9PUR]

IIRC, the reason that warnings signs show voltage is that it looks more dangerous. Which are you more likely to keep away from?

a) Danger: 500,000 volts!

b) Danger: 10 amps!

[Supermike]

Thanks both. I agree high volltage does sound more dangerous than low amps. I thought I must have misunderstood my elementary electricity from my schooldays.

Thanks again M

[LazyGun]

This guy aint scared of no volts ;)

http://www.bbc.co.uk/...ainment-arts-19812217

His latest stunt....

[vascop]

Surely knowing the voltage makes more sense, because the current depends on the resistance it's applied to. More resistance means less current from same voltage.

[HowardKennitby]

It is the amps that ultimately make the difference. While load resistance is a factor it is not the only one.
Electric fences for containing cattle produce a high voltage but the source cannot supply any significant current - thus we do not see lots of electrocuted cattle lying around.
The voltage applied to to the sparking plug of an internal combustion engine is similar. I speak as someone who has accidentally touched the end of a plug on a running engine and I am still here - I think.

[peter_jameson]

Hello Supermike

vascop and HowardKennitby are absolutely correct. Here's a little more for you with a bit of maths:

You would need a current of about 1 ampere in a 1/10th second pulse (much less current for a sustained electric shock) passing through your body to stop your heart.

If we assume that your body has an electrical resistance of say, two hundred and forty ohms, and that is only a guess, then according to the formula: voltage = current multiplied by resistance, 240 volts will be lethal (240 volts = 1 ampere x 240 ohms), however it depends upon the time that the current is available from the voltage source. Obviously, 240 happens to be the voltage of the mains in the UK, so that's why the mains which can supply a current indefinitely can kill you.

We all encounter tens of thousands of volts every day from objects all around us in the form of static electricity, such as by taking off a pullover or brushing our hair but the current is only available for thousandths of a second as there is so little energy available and therefore we are not killed by it. The only result is a slight prickling sensation or we may hear a crackling sound. Lightning is a form of static electricity, but it kills people because the clouds it discharges from are so huge that they can supply a large sustained current through the strike. If your pullover were a mile square, then taking it off would probably be fatal!

So in a nutshell high voltage from say, the mains will certainly kill you so don't risk contact with it. High voltage static electricity from your pullover is safe as it cannot supply a sustained high current.

Regards

Peter Jameson

[Old_Geezer]

As I understand it, it is the current and thus the Amps that causes death. Consider static electricity that for a fraction of time may be thousands of volts, but as soon as a small current flows, the voltage dissipates to near nothing and so you survive.

But since your body will be a particular resistance, the number of amps you pass will be proportional to the constant potential difference, that is volts, either side of you pushing the current through you. So whether you refer to amps or volts as being the danger doesn't much matter.

[shooty]

Its the volts that jolts and the mills (milli-amps) that kills.
The human heart can be put out of sync with as little as 50 milli-amps.
Hence, this is why 30 mA RCD's or RCBO's are now a legal requirement under BS 7671(wiring regs).

In a laymans analogy, If you think of voltage as the speed that electricity is delivered and the amperage as the weight of an object hurtling towards your head -

1. A feather (30 mA) travelling at 400 miles (400 volts) per hour.

2. A house brick (20 Amps) travelling at 230 miles (230 volts) per hour.

As you can see, one of the above will kill you, the other will only hurt.

[Supermike]

Thanks everyone for your very helpful answers. M

[peter_jameson]

Thank you so much for nominating my answer as best, Supermike. Its my first!

ALL the answers are interesting and well informed though...

I've just noticed that you also asked why some people are struck by lightning and survive. Well, the main reason for that would be because with a nearby lightning strike one can get a non-lethal shock from a capacitance-induced discharge. That's too complicated for me to explain here as some lengthy maths and diagrams are involved. Also, having retired from physics a long time ago my poor old brain is getting sluggish these days and I don't want to risk giving you incorrect information. Give it a Google and see what you get, or perhaps some of some of your other answerers can pick up on it?

Regards

Peter Jameson

[Supermike]

Thanks Peter an welcome to Answerbank. As you say all of the answers were very helpful and certainly clarified to situation for me.

Regards Mike