Lighting kills...

[pmbguy]

The other is something that i did a few years ago to prove that you need earth to get electrocuted. I put a few planks on the floor, with a roll of silicone wire, had my safety shoes on. Climbed on the pile with a live wire in my hand, the other end in a plug. Told the guy to switch on the circuit.....nothing, didnt feel squat, proving (to me anyway, in a weird way), that electricity flows to earth, and wont sit in a general mass or something like the sort. I wont try this with anything over 500VAC though

Correct. As you have proved for yourself you need to be earthed to get shocked. BUT dam dude you got big balls. This must have been after a bottle of Jack Daniels and a dare from your mate. Clearly your wife was not around or you would have had testicular swelling from her slapping you, trying to prevent you from your dangerous curiosity. Now that I think about it, it’s actually a good thing she was not there. If she was and she slapped your loins while you were touching the wires she would earth, shocking both of you and leaving you with boiled eggs.

[adrianh]

Correct. As you have proved for yourself you need to be earthed to get shocked. BUT dam dude you got big balls. This must have been after a bottle of Jack Daniels and a dare from your mate. Clearly your wife was not around or you would have had testicular swelling from her slapping you, trying to prevent you from your dangerous curiosity. Now that I think about it, it’s actually a good thing she was not there. If she was and she slapped your loins while you were touching the wires she would earth, shocking both of you and leaving you with boiled eggs.

Define "Earth" - what about a lightning strike between clouds, doesn't that occur because the potential difference is high enough for a spark to jump?

I suspect that you would have to be earthed if your potential relative to the cloud was neutral. What would happen if you were not earthed but you just played with a Van Den Graaf generator

[pmbguy]

Define "Earth" - what about a lightning strike between clouds, doesn't that occur because the potential difference is high enough for a spark to jump?

I suspect that you would have to be earthed if your potential relative to the cloud was neutral. What would happen if you were not earthed but you just played with a Van Den Graaf generator

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

[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.

[pmbguy]

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

[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.