Lighting kills...

[pmbguy]

So being earthed or not is relative to the strength of the differing potential (current strength)

[IMHO]

So why does this stupid guy not get electrocuted?

http://www.youtube.com/watch?v=ut5DXxK1dvk

[Dave A]

So the best bet is not to have such a structure then?

If it's lightning that is worrying you, you're far better of in a metal container than in than a tent.

No one minds getting a contractor to do all the checks but what if the contractor skipped a step how would a layman know?

Out of idle curiosity, do you ever go on or under a bridge? Use a lift? Take a trip in an aeroplane?

The main, relatively obvious thing to look for would be an earth strap between the container metal and (directly or ultimately) the main earth point of the electrical installation. The rest would require electrical testing equipment and a reasonable understanding of the subject.

If I remember correctly, the regs also require that everything is on earth leakage protection. And our experience has been this is where the biggest safety problem starts, especially on big construction sites with this sort of "temporary accommodation unit." The moment nuisance tripping kicks in, some bright spark decides they know enough to "fix" the problem.

What would happen if you were not earthed but you just played with a Van Den Graaf generator

That brings back memories of a misspent student youth. The main thing you (or anyone else watching) will notice is your hair stands on end. And the next time you touch something that is earthed, you're in for the brief whack that goes with a static discharge. It'll sting some at the discharge point if you do it slowly. The best thing to do is grab a water tap - the discharge goes virtually unnoticed that way. Of course, the idea is to charge up, then whack an unsuspecting victim (which somehow seemed to reduce the sting you felt yourself for some reason).

Probably worth mentioning if you're a long haired lout, like I was at the time, your hair stands up in clumps - it's not an even frizz by any stretch of the imagination.

Playing with static electricity amply demonstrates that it's current that kills, not voltage. Of course, you also need enough volts to generate a lethal current through your body.

[Dave A]

So why does this stupid guy not get electrocuted?

High current, but low voltage. Ultimately you could probably cook that rod with a 12 volt car battery (I'd better point out - keep an eye on the battery though - it's going to overheat in more dramatic fashion than that electrical meter did).

Effectively he's made a step down transformer. And he makes sure he's not earthed when holding the rod.

[adrianh]

Hey I just fix printers I am certainly no expert in the field but I think that when lightning travels from cloud to cloud its because of differing potential between the two being great enough for it to jump. Lightning works the same when it hits the ground, its because of the differing potential between the clouds and the earth. The stronger the current the bigger the gap is it can jump, so you might think you not earthed but if the current is big enough it will jump, so passop met daai genni

I don't think that you should be using the term current, it is potential difference, current is a measure of flow of energy over time. Isn't it 1amp flows through a wire at 1V with a 1omm resistance over a period of one second...or something like that whereas potential difference is the sum of negativity vs positivity of the objects being measured. I suspect that excess electrons are pulled free if the potential difference is high enough or of course added if the potential difference is high enough. So, in essence a whole bunch of electric charge moves at one hell of a speed (it's got to be the speed of light otherwise you wont be able to see it from one point to another because the one point sorely wants to get rid of all the excess electrons that it carries. I would think that the voltage would be extremely high and also the resistance V=IR thus I = V/R which means that if the voltage is very high and the resistance is very high then the current is going to be very low.

I think that a good analogy is hydraulics (pumps and water flowing through a pipe) High voltage low current would be a massive pump pushing water through a thin pipe at a very high pressure. So in an lighting strike you have a massive build up of charge and when the arc jumps the energy moves from one point to another at the speed of light. (Massive pump - little pipe = high speed) Low voltage high current would be a less powerful pump moving lots of water through a big bipe which of course = low speed.

I think that this is the reason the lightning strikes cause such terrible burns. A huge amount of emery is passed through the body in an instant probably causing water to vaporize within the body. This is probably also the reason why people have a better chance of survival if they are wet, the energy takes the path of least resistance that would be the water outside the body. The water may vaporize, like it does when you wet your finger and touch a soldering iron but your finger is ok because the water dissipates the energy when it vaporizes.

Low voltage high current probably stops your heart and blows your mind because there is a lot of energy flowing at a slower pace. Those little circuits in your body simply get overwhelmed and f*ck out because they cannot cope with the continual flow of lots of energy.

Ok, these are all my layman's theories and they may all be total crap!

http://en.wikipedia.org/wiki/Electrical_burn

Electrical burns can be classified into six categories, and any combination of these categories may be present on an electrical burn victim:

Low-voltage burn. A burn produced by contact with a power source of 500 volts or less is classified as a low-voltage burn. The current at this voltage is not enough to cause tissue damage along its path except at the contact site. This type of burn may be mild, superficial, or severe depending on the contact time.[10]

High voltage burn. This burn is very severe as the victim makes direct contact with the high voltage supply and the damage runs its course throughout the body. Exterior injuries are misleading as most of the damage occurs underneath the skin. In this case, subdermal tissues are severely damaged.[5]

Arc burn. This type of burn occurs when electrical energy passes from a high-resistance area to a low-resistance area.[7] No contact is required with an arc burn as the electricity ionizes air particles to complete the circuit. The heat generated can be as high as 4,000 degrees Celsius - hot enough to vaporize metal and ignite a victim’s clothing. A form of explosion dissipates excess energy from the arc.[10] In addition, a high-amperage arc can produce a pressure wave blast in excess of 1000 pounds per square inch of pressure. This can throw the victim and cause severe injuries.[11]

Flash burn. Flash burns are caused by electrical arcs that pass over the skin. The intense heat and light of an arc flash can cause severe burns. Although the burns on the skin are largely superficial and cover a large area, tissues beneath the skin are generally undamaged and unaffected.[7]

Flame burn. Associated with flash and arc burns, flame burns are caused by contact to objects that were ignited by an electrical source.[7]

Oral burns. This is caused by biting or sucking on electrical cords, and it most commonly happens to children.[12] Electrical current typically passes from one side of the child’s mouth to the other, possibly causing deformity.

[tec0]

So why does this stupid guy not get electrocuted?

http://www.youtube.com/watch?v=ut5DXxK1dvk

You get crazy and you get stupid crazy. If you check the last bit of that video his finger was so close to become the shortest path between those two thick wires and with the amount of AMP they were playing with... He wouldn’t have done anymore thinking for a good long time. BUT he got lucky... I wouldn’t do that... I got my own Tesla coil that I play with but nope I wouldn’t do that...

[pmbguy]

I heard that its not the amount of voltage that kills you but that its the amount of Amps that will determine how dangerous the shock is. Is this true?

[adrianh]

This is also interesting to think about; the guys that do live HV line maintenance. They wear suits that are essentially faraday cages capable of carrying the current. The guy inside is ok because the current flows around him. He gets picked up off the ground by a helicopter and a long insulated cable which insure that the helicopter doesn't get electrocuted. I suspect that when is picked up and lowered to the ground he would have to dangle a cable hitting the ground so as to dissipate the charge to ground so that is cage has the same potential as the ground.

[adrianh]

No, its not necessarily true. Possibly for 12V - 220V but 200,000V low amps will cook you like a microwave and 12V 100amp will stop your heart and blow all your circuits.

[adrianh]

Think about connecting a 300mA 100V transformer to a 12V radio. The radio ain't going to work anymore .

[adrianh]

You get crazy and you get stupid crazy. If you check the last bit of that video his finger was so close to become the shortest path between those two thick wires and with the amount of AMP they were playing with... He wouldn’t have done anymore thinking for a good long time. BUT he got lucky... I wouldn’t do that... I got my own Tesla coil that I play with but nope I wouldn’t do that...

It's not a big deal at all. He is using an isolation transformer. It means that the transformer is not referenced to ground. That is exactly the type of transformer used in your swimming pool light. You have 220V coming into the primary side on the transformer and 12V coming out the secondary side. Lets say your light gets messed up and the wires are exposed in the pool nothing happens to you. If they secondary side of the transformer was referenced to ground you would get cooked. Because the transformer is not referenced to ground you get 12V floating about in the water that doesn't do too much harm. Remember that water is a good conductor and that the electrical energy now dissipates through the water.

A isolation transformer can be thought of in the following abstract way. You are sitting on earth and the earth is travelling at 64,000kmh relative to the sun. You now get in your car and travel at 100kmh. The speed difference relative to the sun (common electrical earth in this case is massive at 64,100kmh but you are measuring your speed relative to the earth (lets call it unreferenced electrical earth) and you are travelling at 100kmh.

[tec0]

First and foremost “I am not expert” Secondly I stand to be corrected otherwise I will probably get someone screaming about details again. So I start with the facts here

The Fatal Current

Strange as it may seem, most fatal electric shocks happen to people who should know better. Here are some electro-medical facts that should make you think twice before taking that last chance.
It's The Current That Kills

Offhand it would seem that a shock of 10,000 volts would be more deadly than 100 volts. But this is not so! Individuals have been electrocuted by appliances using ordinary house currents of 110 volts and by electrical apparatus in industry using as little as 42 volts direct current. The real measure of shock's intensity lies in the amount of current (amperes) forced though the body, and not the voltage. Any electrical device used on a house wiring circuit can, under certain conditions, transmit a fatal current.

While any amount of current over 10 milliamps (0.01 amp) is capable of producing painful to severe shock, currents between 100 and 200 mA (0.1 to 0.2 amp) are lethal. Currents above 200 milliamps (0.2 amp), while producing severe burns and unconsciousness, do not usually cause death if the victim is given immediate attention. Resuscitation, consisting of artificial respiration, will usually revive the victim.

From a practical viewpoint, after a person is knocked out by an electrical shock it is impossible to tell how much current has passed through the vital organs of his body. Artificial respiration must be applied immediately if breathing has stopped.

The Physiological Effects of Electric Shock

The chart shows the physiological effects of various currents. Note that voltage is not a consideration. Although it takes voltage to make current flow, the amount of shock-current will vary, depending on the body resistance between the points of contact.

fatal current

It is also fact that if you have a weak heart that the effects might be worse for you.

[tec0]

Now I didn't know half of this...

[tec0]

This is scary stuff...

[Jacques#1]

Here is a question, lets say you were to get very close to a 32KV line (you do not touch the line), would the electricity to induced on your body by the ionisation of the air around the cable or static electricity or simply by the magnetic field. There is a line that runs close to Grand West and I often pass by it. The sound that comes off the line, I suppose due to the ionization is very noticeable. I wonder what sort of effect the general electrical and magnetic discharge from those line have on animals.

I had a callout a few years back on an electric fence (yes, the fence was erected by an idiot). Anyway, they had an alarm. So the first thing you do is disconnect the HT cables and bridge out the energiser terminals to determine if its an earth fault or a continuity fault. I switched off the energiser and it still smacked me. I quickly carried on connecting with the constant coltage on the line (used to getting choked I guess). I checked the voltage on the line and it was around 1300V. After walking through this unknown 1.5km fence around a complex, I noticed that it had NO earth spikes, and an overhead line running parralel straight over about a 500m section of the fence. If there was spikes, I wouldnt feel the voltage, but the emf had no where else to go except constantly through the wires.