Electric Shock

Well unlike this imaginary hole in the ozone layer, this can be proved and verified if you wish to try it. Unfortunately however it may be the last thing you ever do and you will not be around to tell the tale. You could of course have a self experiment witnessed and at least independent witnesses could verify that you were thrown across the room before you died as a result of a fatal DC current electric shock.

I am not a pathologist but as an electrical inspecting engineer I have been called upon to investigate a number of fatalities involving AC fatal electric shocks. I have never investigated a DC current situation, but I did have to contribute towards implementing safe working practices as a result of an indecent .

The crux of the matter is that the muscles in our bodies are activated by electrical impulse messages sent down from the brain.

Some signals like the message to the heart to keep beating, ears to keep listening, nose to keep smelling and breathing, and lungs to keep inflating, are all sub conscious and are taken care of by a part of the brain which carries on working regardless of what you are actually concentrating on. Just like a computer processor it is taking care of things in the background while you use the whole system for dedicated tasks such as sending a signal to lift your right arm with that pint of beer in the hand.

These electrical signals are however minute and don't work off the standard 9v battery. When a person receives an electric shock from a substantial source, the electrical current is far more excessive that the normal body signals. Therefore instead of getting very small microvolt signal to the muscles in your body, arms and legs, they are subjected to this massive signal which overrides the normal function signals sent from the brain and therefore they respond in a sudden violent reaction.

There is no invisible force which picks you up off the floor and throws you back against the wall, the amount of movement will depend upon the position of your limbs.

DC current provides just a constant violent signal which appears to throw the muscles open to their extreme extent.

If you were part crouching with your knees slightly bent or your arms bent when receiving the shock then your legs will straighten violently and your arms would tend to throw wide open. It is this violent movement which changes the position of the body and is perceived to have thrown you from the point of contact.The medical heart start machines are DC and as you may have seen on the movies, the patient can lift of the table when the current is applied.

AC current, because of the sine waveform gives you a shock 50 times a second on a 50Hz supply and this results in a extremely violent throbbing, vibrating feeling. This time the muscles are subjected to these excessive and duplicate, conflicting messages and they do the opposite - they fully contract. The hands that may be making the electrical contact close and grip firmy, making it impossible to let go. The heart also fully contracts and stops pumping, therefore it is eventually fatal.

If you see anybody in this situation and you go and grasp them to help, you will so succumb to the same fate, you must use a non conductive rope or scarf to pull them away, or a piece of wood to knock the legs away from them. Even if you break their legs you may still save their lives.

In both cases that is not to be confused with blast injury. If a person is exposed to a high current exposed contact situation in the vicinity of a ionised air short circuit, the energy which released is substantial and similar to an explosion. In such circumstances a person could be thrown across the room just by the force of the explosion irrespective of whether or not they have actually received a shock.

Hi Guest,

Most informative! Enjoyed your take on the matter. I understand that it takes less than 1 amp to be fatal. Is this correct?

Can you explain how a person is killed, say, if that person in in a bathtub full of water and someone throws an electrical appliance in to the water? You oftentimes see such things in movies, i.e., Goldfinger, I believe, right at the beginning. In such a scenario would it be fatal if there were no grounding? For example a person in a plastic tub with no metallic faucet, drain, etc.

Just curious.

John

Also, what is the electrocution mechanism if one is in a swimming pool when lightening strikes?

I think about 500mA is in the ballpark for fatal. It is possible to survive marginally higher strength current, but if the current runs through your heart and makes it contract, you're down and out for good. If you're not dead, I think you'd still have some really nasty electrical burns.

30 - 50 ma is more like the minimum threshold to induce cariac fibrillation, and that's about what gfi's are set for

100 ma (1/10 amp) across the chest is all it takes.

Hi Kyoto , you must get googled an awful lot !

Just guessing, but the body of the water in the tub may be enough of a grounding agent in itself. Meaning no direct connection to any other ground is required. The volume of water itself will do the trick. I'm not sure how much water it takes to become an electrical ground.

That being the case, the water becomes electrified and if you are in it so do you. For example a boat in the water with a polarity reversal and a short circuit can electrify the water around the boat and electrocute anyone swimming there.

But Kirchoff's laws still apply. You still need a complete circuit.

Hi sail4evr,

You said: "the body of the water in the tub may be enough of a grounding agent in itself. Meaning no direct connection to any other ground is required."

That just doesn't add up!

Also you said: "the water becomes electrified and if you are in it so do you."

What about "hot workers", those guys that sit on those 500kv lines and work. Just like birds sitting on high-voltage wires. Very happily, I might add. So it seems like just sitting it the water and becoming electrified (long as you're not externally grounded) should, it seems to me, not be a cause for concern.

Take a situation like I mentioned earlier. Say I'm in a swimming pool and a live power line breaks and falls into the pool. How does the current flow through the water, then through my body, to ground to complete the circuit.

Granted, the current can flow through the water then through my body, but then where does the current flow? Back to the water which is still at the same potential as it was when it went into my body? Doesn't seem like there's a path here.

Are you saying that possibly the water acts like a giant capacitor that sucks up the current, causing it to flow through my body? This seems to have more merit than anything I've heard so far.

What am I missing?

John

I'd have thought the water would be a pretty poor conductor unless is was heavilly dosed with detergent or some such.

We use conductivity sensors in commercial dishwashers, and plain hot water is not very conductive especially in soft water areas.

Interestingly the EN spec for commercial dishwashers allows upto 30ma leakage current which is plenty to mess up our probe reading which is driven by a 5v pulse!

Fortunately this doesn't often happen, just try explaining this to the 'engineer' (fitter/installer) over the phone.

Wost shock I've had was 2kv across my hands....I worked in development test and was testing a power supply. I put my meter across the 6.3vAC terminals on the test rig to measure....The idiot who designed the rig didn't label it as being up at 2KV ! and there was no safety cover. (e.g 1 terminal at 2kv DC with 6.3v ac between the two!!!) It knocked me back about 3 foot... and made all my fur stand on end!)

C'est moi!

Fur-got to log in...

Just to clarify folks - there was a reference to fur here , but it sure wasn't me posting. Can you elaborate on the post Guest - I'm curious. I don't mean to sound flippant but it sounds like you had a mega (aka insulation tester , etc) attached to your fingers ! I'm trying to picture what you describe , but with some difficulty.

"I'd have thought the water would be a pretty poor conductor unless is was heavilly dosed with detergent or some such."

Fresh water certainly is less conductive than dirty or salt water and that is part of the problem. The less conductive the water the greater the voltage you will get for any two points that are at the same point and distance apart. If the water is more conductive than your body than the majority of the current will flow through the water that surrounds you body. If however the opposite is the case and you are more conductive than the water then the current will be concentrated through your body and you will cop a stronger belt.

Sea water is pretty close to being as salty as the human body and so has roughly the same conductivity and to electricity it sees little difference. With fresh water you are considerably saltier and so more conductive and you will therefore get a considerably more powerful belt.

Something else that needs to be considered is the distribution of the current through the medium. As I described earlier the current flows between the two contact points and disperses like the magnetic field of a bar magnet. The dispersion pattern is controlled by how conductive the medium is and a less conductive medium causes the electricity to disperse over a larger are. It sort of like having one resistor connecting the two terminals with salt water or hundreds in parallel with the fresh water. With the hundreds in parallel the current is flowing over a larger area.

It sounds strange but this all adds up to you getting a bigger and possibly more lethal belt from fresh water than dirty or salt water and it may be the difference between surviving or not.

At least that's what the theory behind it says, but, I would not recommend trying it at any time especially if you live in Australia where we use a 240 V three supply.

I'm confused!

Can we clarify?

If you are in the fresh water, and the two terminals with the applied voltage are in the water but not touching you I don't see how you will get a belt.

If you grab one terminal and the water is a poor conductor where is the return path?

If you grab both terminals...af course you will get a belt...'cos then the water is then irrelevant.

Wost shock I've had was 2kv across my hands....

I wasn't even thinking water . A fairly common voltage to test for insulation on a domestic appliances will use 2Kv . Just wondering sort of ! Most people worry about radiation with microwave ovens , but open one up and you may find a better reason to worry with the capacitor. Not recommended for the unwary or faint-hearted. With the switch off , a killer shock lies waiting. Insulated grips to short it out make an impressive noise - I'd hate to be on the receiving end !

"If you are in the fresh water, and the two terminals with the applied voltage are in the water but not touching you I don't see how you will get a belt."

Fresh water isn't a good conductor of electricity but it is a conductor and there will be a current flowing from one terminal to the other. As I indicated this current will flow between the two terminals in a manner that looks very much like the lines of magnetic flux from a bar magnet.

Depending on where you are in relation to the two terminals will determine the sort of voltage that you are subjected to, but, in something the size of a bath I can guarantee that you will definitely know about it.

PS The reason water is conductive comes from the shape of the molecule. The two hydrogen atoms are not 180° apart and so the molecule is bent with one side being slightly positive and the other slightly negative.

Ok... ta!

But the lethality (did I just make that word up?) will still depend on the distance between the terminals relative to the vital areas of the body.

So in the James Bond case..it's no good throwing the electric fire into the end down by your victims feet as the 'lines of flux' won't reach up to the body to kill 'em..but their feet will be rather cosy!

Hmmmmm, I'll leave the test and proving to those more foolhard!

"But the lethality (did I just make that word up?) will still depend on the distance between the terminals relative to the vital areas of the body."

No you didn't just make up the word lethality it is a real English word.

The electric shock part is correct as well and it all depends on where the electricity contacts water in relation to your chest. There was a series of experiments carried out on the Mythbusters program bit it was using American supply voltage fresh water. They did however produce what would have been a lethal current through the chest of a dummy that was in the water so it can be lethal.

Hi Del,

Guess I'll just stick with showers. If I have to take a tub bath I'll just use DI water and let the villains come.

On second thought, they'll probably hit me in the noggin with the lamp and do me in anyway.

Cheers

Amen to your last paragraph.

I once did a 'forensic` on a shorted 480V. BusDuct.

There were globules of copper embeded in a cinder block wall.

Also, the tendancy for ac current to run on the outside of the conductor (hence tube cunductors) as opposed to the tendency of dc current to run in the center of the conductor, means the insides are fried more in a dc electrocution.

RichH

hmm

good qs. i m waiting for an answer

Also worth remembering (in case anyone thinks that they have had a lucky break to live through a relatively high-amp shock) that electric shock and lightning strike victims frequently die some weeks later from cerebral hemorrhage... The heart may have survived the shock, but the current flow through the blood can do some nasty things inside veins and arteries, causing curdled and clotted blood.

Bottom line - after any decent shock, get yourself to the doctor.

It's 30 years since my 2kV belt...am I too late to go the doc?

Back to the water!

Sea water of course is nice and conductive...sea water used as electrolyte (google sea water battery).... and of course the sea is grounded.

If you had a glassfibre/plastic/perspex bath with plastic water and waste plumbing one can only assume you would be floating! (lol)

Referring to the earlier posted situatoin -- sitting in bathtub and a non-friend throws an electrical appliance into the tub ---- appliance is shorted to ground via metallic drain pipe and plumbing. Toaster/radio/hairdryer pops fizzes and dies (maybe the fuze circuit breaker/ground fault interupter pops and breaks the circuit) --- you may be a bit suprised but otherwise unharmed -- although you are immersed in the water, you are not part of the series circuit and observe rather than participate in the electron transfer (personal experience - very angry EX-wife) If you however, posess fast reflexes and reach out to grab the aforementioned appliance, you may well provide the "fusible link" in the chain from mains power through your body to the well grounded tub full of water - In this case your nerves, blood vessels and all electron paths from your hands to those body parts immersed in water will fry/pop or sizzle like any other weaker link in the chain. Will the 15 amp fuse or circuit breaker pop before your heart or nervous system? Anybody's guess and not really something to take a bet on.

Good answer Guest. Makes sense. Glad you made it through being a first-hand observer.

John

Ask Roy Sullivan or the BBC

No, I'm not gonna ask Roy.

If I got within speaking distance of that man I'd probably get hit!

The smart move would be to invite him for a stroll , but have him walk about 5 yards to one side. OMG , I may have sparked debate about how far Roy needs to be to act as a safe conductor ! If not , make Roy carry an umbarell . He sounds used to it anyway .

Ok what happens with the toaster in the water is that you are throwing an active wire, that's the dangerous one, and a least a neutral wire and most likely an earth wire as well. The neutral wire is not normally switched and the earth wire is never switched.

What happens is the electricity flows through the water from the active wire to the neutral or earth. Electricity likes to take the path of least resistance for the most but that doesn't mean the flow of electricity between the active and neutral/earthy flows directly between the two points of contact with the water. The current actually spreads out in a pattern that resembles the lines of magnetic flux that you see when you sprinkle iron filings on a bar magnet. Imagine the N and S are the active and neutral.earth and you will get the idea how the current disperses through the water.

Now this is where it really starts to get complicated. The voltage between any two points is proportional to the resistance between those two points and the current flowing between them. You can set up an experiment with a battery and a couple of terminals in fresh water then using a multimeter check the voltage by sticking the two leads of a multimeter in at various points.

As the guest in post #12 pointed out a current of 30 to 55 ma passing through the heart is all that it takes to cause the heart to stop beating. What this means is that if you are in the water and a current is flowing through the water and there is sufficient voltage across you chest to produce the current there is a good chance your heart will stop and if not started again within 180 seconds you are history.

One of the factors that is critical is the conductivity of the water. The more pure the water the less conductive it is and so the greater the voltage you will get between any two points. If the water is highly saline then the voltage between two identical points will be less. If the water is more saline than your body in general the electricity will tend to bypass you and flow through the water. The upshot of this is that in salt water you will get far less of a jolt than in fresh water and it may be the difference between surviving or not.

The lightning is a different thing entirely because the voltages are extremely high and will cause just about any insulator to break down. With the lightning the point that the lightning hits is analogous to the active wire and everything else that surrounds the water is the neutral/earth. The current will dissipate in a radial manner in three dimensions from the point of contact. The only difference between lightning striking the water and ground is that the area over which the current dissipates will be much smaller in water and the currents in that constrained area will be considerably higher. The same thing as the bath applies and if there is sufficient voltage across you chest in the water to produce the 30 to 55 ma through your heart you are in big trouble. You do however need to be closer to the strike point in water than on land and in salt water, because it is more conductive than your body, the effect is reduced.

There is an interesting feature with lightning and it comes back to the voltage drop you see at points that are different distances from the point of contact. The greater the difference in the distance two points are away from the contact point the greater the voltage you will see. This sometimes manifests itself on a farm if lightning strikes a paddock where sheep and cattle are both present. Some of the cattle will all die while all the sheep survive and the reason is the increased distance between the cattle's front and rear feet. The greater distance between the cattle's feet causes them to be subjected to a greater voltage than the sheep,

The upshot of all this is that if you find yourself caught out in a field in a lightning storm then crouch down and keep your feet together and stay as far away from items that are likely to get hit as possible. Lying down is not a good idea as it will mean that there is a greater distance between the points of contact with the ground and so increases the voltage you will be subject to. Oh yes, lightning dose strike twice in the same place so if somewhere has been hit previously stay clear as it is likely to get hit again.

The best place to protect yourself from lightning it to hide inside something that is conductive like a car. What happens is that the energy travels through the metal of the care and on the inside cancels out the effects. This is actually called a Faraday cage and you can read more about you they work by following the link. An interesting adaptation of the Faraday cage that works well for areas that are prone to lightning, is to bury a loop of un-insulated copper wire about 12 mm thick around the base of the structure. If lightning strikes nearby the area inside the loop is protected by the loop in the same way a Faraday cage works.

masu , your response is , as ever , comprehensive accurate and informative. Pause. I'm going to risk questioning a couple of point. My motive is that I have no idea how much knowledge any reader has. If I can reasonably stir ther pot , increased knowledge may result (probably for me ! ). Perhaps others may learn through my childhood naivety.

Lightning : The direction of the flash observed has only recently been discovered. I won't elaborate because my knowledge is not total on this , and ambiguity of terms may arise if I attempt to explain. It has no relevance in relation to whether a person gets killed by lightning or not , it simply illustrates the debate on the topic. I will simply say anybody should investigate which way a lightning strike flashes in slow motion. It may help to understand the nature of the topic.

The above point has some relevance in relation to which way electricity flows. In practice flow' can be considered as negative charge one way or 'positive' holes flowing the other way. This is a fundamental aspect of electricity , and again I will not elaborate because it is a potentially serious subject and requires better explanation than I can give. By way of explanation I will explain a personal experience ;

In the 70's my parents owned a house that was built (and probably modified many times before) decades earlier (this occurred in the 60's). I tried to sort out a broken light-bulb , assuming (in my early teenage years) that it was safe with the switch 'off'. So , switch 'off' and fingers in light fitting ;

Big mistake. In a typical circuit , a light fitting can function as if perfectly normal whichever wire is 'switched'. IT SHOULD ALWAYS BE WIRED WITH LIVE SWITCHING. If it is incorrectly wired with neutral switching it will appear to a user as normal , but the fitting is still live when apparently (from hitting the switch ) turned off. My early discovery of this fact , whilst painful , was one factor in my engineering interest. I can fully assure you that AC shock does (as stated earlier) cause mussels to contract. Balancing on a chair will cause you to fall (despite your mussels inclination) , and hopefully break contact before you're dead. Painful though.

The above point is not directed at the original question or masus response. It's simply chucking in my two cents in case anybody comes across this site and doesn't have a reasonable knowledge of electricity. My inclination is not to admit I was an ignorant kid once , but in the interest of greater good I relate this so somebody may learn from my experience. In short , If you aren't certain don't play.

Taking the latter point masu , there was a nice example of Faraday cage effect on the BBC show 'Top Gear' . I wont elaborate - anybody puzzled will find out more by looking it up , and there are people more qualified than me to explain. My intended delay in information will make the point 'look before you touch'.

As I always like to end on a light note , it would make a good discussion thread to post 'Engineering confessions/embarrassing mistakes'. Does anybody think it worth initiating ? I have zero shame about mistaken knowledge - it can save lives , trouble , and give all a good giggle in the process. What think ye all ? Specific electricity questions can be answered here , but perhaps a general humorous/funny confession thread on engineering related mistakes may serve a useful purpose.

Hi Kris,

As I always like to end on a light note , it would make a good discussion thread to post 'Engineering confessions/embarrassing mistakes'. Does anybody think it worth initiating ? I have zero shame about mistaken knowledge - it can save lives , trouble , and give all a good giggle in the process. What think ye all ?

Sounds like a good idea to my and you have my support.

On the subject of people switching the neutral line instead of the active, it can be a real nightmare.

I had a similar problem when I was working an a computer control system for a skyscraper. One of the electrical apprentices that was installing a sensor complained that he got an electric shock while connecting a reed switch that checked that a fire door was closed. He complained to his supervisor who told him he was imagining things as it was only a 5 V signal from the computer. None the less the apprentice insisted and the supervisor decided to prove it was safe by touching the cables. After he picked himself up of the floor he came screaming to me that complaining I was trying to electrocute him. I gave him the same story he gave the apprentice so he said come with me. I was a little more cautious and used a test pencil and multi meter and was astounded to find that there was 110 V AC on the cables.

The problem was fare worse than we thought as we soon found that somehow there was 110 VAC on the low voltage common ground line and that every common ground on the entire system which included several thousand separate sensors had 110 VAC on them. The low voltage common ground is not connected to earth so it did not affect the operation of the computer but you got one hell of a belt if you touched any part of the low voltage circuitry.

It was pretty obvious that somewhere somebody had connected a 110 VAC active to the computer systems low voltage common ground but with several thousand separate sensors where do you start. Compounding the problem was the fact that the voltage would come and go making isolating the source even harder.

We ended up having to shut down the entire building incase somebody got hurt and using the principal of halving the system we tracked it down to a lift control panel that had just been started up and was in the process of being commissioned. The lift system used some really strange colour codes and voltages and the people that installed the interface between the lift system and the computer system had mixed up the wires and connected a wire with a switched 110 VAC signal on it to the common ground. We were lucky because the building was not finished and so there were few tenants but it took the best part of a day to isolate and inconvenienced a lot of people.

Something to watch out for with modern electronics is that triacs work better when used on the neutral side of the load. There should be some secondary circuit that can be used to isolate the active line from the load but like the situation that Kris found you can never be positive and it always pays to check before touching.

phew - sounds like quite a mess. As you say , it was lucky from a problem solving point of view that not too many tenants had moved in.

In the UK every Bank Holiday leads to scores of injuries as amateur DIYers to a bit of home improvement. The situation is perhaps worse now - high market prices mean people tend to stay put and increase house value with DIY. The law has tightened on home electrical work but not much - a person merely has to be 'competent' whatever that means - no specific certificate of ability is needed (correct me anyone if I have this wrong). The screw up of using neutral switching on light circuits happens quite a lot. I wouldn't trust things even on a new build house. It's no big deal to do a visual check behind a few face plates and use a socket tester for polarity and earth loop impedance etc. I'm not a qualified sparky , but I'd certainly look for any glaring errors.

There is currently a thread about somebody's plumbing problem. It sounds like a landlords DIY mistake to me. As ever the rule should be 'don't play with it if you don't know what your doing' , but some DIYers get a bit too enthusiastic and people will always try to cut corners on hiring a pro. I'm still mulling over a possible thread title - there is a lot of possibility for various accents on topic. I'll let this sit here for a couple of days and see what I hear.

Cheers , Kris

Hi Kris,

You said: "the rule should be 'don't play with it if you don't know what your doing' , but some DIYers get a bit too enthusiastic and people will always try to cut corners on hiring a pro. I'm still mulling over a possible thread title - there is a lot of possibility for various accents on topic."

Several years ago when refrigerant R-12 was it for automotive AC use (before R134A) there came a time when such an uproar was made about CFC's polluting the atmosphere that certification was required before one could purchase it. Certification consisted of taking a written test, mailing it in, and, if you passed it, you were issued a certificate & a wallet card by mail. A retailer would sell R-12 to you only if you presented the card (this was, and is, a law in the U.S). Not too many folks using R-12 any more though.

Certification did not mean that you were in any way an expert in the use of CFC, but mainly that you understood the importance of capturing and recycling CFCs and that you would not wantonly dispense the stuff into the air.

The point I'm trying to make (if there is one) goes to your "future" thread. What do CR4'ers think about some sort of competency test for DIY'ers, especially when it comes to "dangerous" components such as most electrical (other than face plates, etc.).

As you said: "a person merely has to be 'competent' whatever that means - no specific certificate of ability is needed "

Such a test might cure ignorance, as the saying goes, but certainly not stupidity. DIY'ers the world over will probably have their shorts in a wad over a suggestion like this but it's just food for thought anyway.

Such a test might prevent a lot of heartache if a "civilian" is contemplating the purchase of something like a:

"DRILL PRESS: A tall upright machine useful for suddenly snatching flat metal bar stock out of your hands so that it smacks you in the chest and flings your beer across the room, splattering it against that freshly-stained heirloom piece you were drying."(as Milo said in This list of tool names came in my email)

Cheers,

John

Hi john ,

lots if interesting issues in that - CFC handling is almost a forum in it's own right . The certification bit is interesting. For portable appliance testing (PAT in the UK - refers to mainly 'white' household appliances) a person can obtain a recognized certificate. It is effectively handed out for a fee in return for attending a few hours at some dubious colleges. The requirement to have the certificate is also not there in legislation. Things may hopefully be better outside the UK. My point is that if the government can't regulate professional trades-people , they have no chance with home enthusiasts. Gas work (in the home ) is normally done by Corgi registered people. Most consumers are not aware that a CORGI card in itself means nothing. I have seen tradesmen try to do work they are not certified for (most folk do not know to look on the back of a CORGI card to see what the person is qualified + legally allowed to do). There are many good field Engineers working in the UK home market , but there is an awful lot of rogue ones.

I'd seen milos thread - great fun , though 'many a true word is spoken in jest'.

What do you think - 'botched engineering in the home' or 'embarrassing lessons learnt' ?

Kris,

You said: "My point is that if the government can't regulate professional trades-people , they have no chance with home enthusiasts"

The suggestion I was making was to regulate retailers and thus home enthusiasts indirectly.

Of course the retailers would then be up in arms as well as the DIY'rs and this would probably lead to massive protest marches which might then, conceivably, degenerate into immense hoarding of light switches, gas valves, etc. Black market would thrive. Maybe not such a good idea after all but still something on the palette for thought.

John

I see what you're saying John.Let me elaborate -

I don't know how things work in the states , but over here the more the government try to stop you doing something the more folk want to do it. This is probably truer in the home than any other place. Most hardware stores are pretty responsible about warning people of dangers/laws etc. In theory , an ordinary Joe should not tackle anything more than change a light bulb at home. I would have no hesitation in fitting extra power sockets and so on. I am also looking at the consumer unit (main inlet fuse-board) with studied intent. I'm well aware of the 60 amp that can flow before the 'service-head' blows , and working live is not my thing (however I know many that would ! ). I will possibly use an underhanded method to get the power company to isolate it for a few hours while I do the job. They are welcome to inspect afterwards - I shall say a 'qualified person' did it if asked.

Just for general interest , the 'car-boot sale' is a thriving black market industry here. People hoard tools and components (the harder to get hold of , the more people want them ). My own tool kit is , shall we say , 'comprehensive' .Most components can be purchased in any high street store (even though people can not supposedly install them). I wouldn't go near gas jobs with a 10 ft barge pole (English expression) , but anything else , well

Just in case anybody from a UK power company is reading , my suggestion of working on a consumer unit is just hypothetical. honest.

Kris

Oh my goodness - I'm the guy that posted the first reply and never realised how things can get out of control - from toasters in the bath tub to dodgy workmen.

I will endeavour to offer some answers to some of the questions bearing in mind that all references are to UK standards.

10mA is sufficient electrical current to upset the heart rhythm and cause fibrillation, but RCDs set to this current are practically useless due to nuisance current tripping as all installations have a certain degree of leakage.

10mA RCDs are available and indeed are specified for extremely hazardous conditions - such as TV repair workshops, because TV sets traditionally worked with a Live metal chassis.

Next pure distilled water is a very bad conductor of electricity, it only becomes a conductor when impurities are added particularly minerals. In fact the purity of water is measured by its conductivity - such as power station boiler water. Low conductivity is relatively pure, but when the conductivity rises it has to be treated to remove impurities.

Traditionally baths were made of cast iron or steel - both excellent conductors and they were well earthed by lead or copper pipes, in bygone days the electrical installation usually used the water pipe as the main earth.

In todays modern world of fibre glass baths and plastic pipes and wastes - the James Bond scenario might not have worked.

The wet body is a very good conductor and house water will contain some degree of minerals and therefore will conduct, so if you have an ample behind which itself is in contact with a large mass of steel, the current will most certainly travel the path through you body, unless it the Live part touches direct against the bath itself.

Many people have been electrocuted in this fashion by taking portable radios, TV sets, etc. into the bathroom.

The UK regulations specifically prohibited any switches or sockets located in a room containing a bath or a shower.

The gentleman man who was in difficulty in the swimming pool is indeed correct - if you are treading water and not touching the bottom or sides of the pool then you will not create a path and therefore in theory will not get a shock, mind you the simple act of power line falling into the pool would be a big enough shock for me!

But the concrete shell of a swimming pool under the tiles incorporates a steel reinforcing cage which again is well earthed and if you are in contact with the floor or sides, the mass and surface area of you body will present an excellent conductive path.

It all about potential difference, if you are touching the ground or any earthed material then you are earthed at the transformer reference point.

Similarly when you are touching the live part and no earth then you are at the potential of the Live source and are safe - its when you have a foot in both camps that the trouble starts

When we talk about our bodies not being conductive when immersed in water, remember our bodies are 80% water more or less with lots of salts and other minerals thrown in.

As a marine electrician (ABYC certified), among other things, we were taught that if a boat has a faulty circuit breaker (that doesn't trip) and something shorts out to ground and the boat is grounded into the water through a metal keel or an engine shaft and prop or a ground plane, an electric current will pass into the water and thence electrify the water around it to a degree depending upon the size of the shorted current. If in fact someone is swimming in the water immediately around this boat they will be subject to electrocution. I don't recall whether they actually gave a case study about someone who was so done in that way, but I tended to accept what we were taught.

If you all refute this, I can go back to instructors more knowledgable than myself for a more succint documented case study.

On US Naval vessels, the 3-phase 450 AC distribution system is ungrounded as opposed to a typical landbased system. If one leg grounds itself there will be no big problem; but if two, well then, there's fireworks and the circuit breakers trip. This system was derived to prevent loss of power to battle damage. Even though the power system is ungrounded, you can still get electrocuted due to the capacitance between the current carrying conductors and the steel hull. Typically, the voltage is about half between a live conductor and the hull/ground, but for some reason the measured voltage varies depending on where you take your measurement.

Regarding one response about grounding a residential distribution system to the home water piping, the National Electrical Code, which is the electrical bible for installations/inspections in the US still requires the grounding conductor be attached to a cold water pipe. This is in addition to a required grounding rod. Back in the 70s, I was living in a house on the beach in SC. One day I was standing barefooted on the tile floor in the bathroom washing my hands in the sink and thought I felt like a was getting a slight shock from the water. I could not believe what I was feeling. Water is grounded for God's sake. I got out my old trusty VOM and stuck one lead in the toilet and the other in the water stream from the sink. The meter was reading 20 volts. We called the owner of the house we were renting and she called an electrician who came over and removed the ground wire from the cold water pipe. I said, you can't do that, the NEC requires it be connected. We don't go by the NEC here he said. Oh well. We went out to the meter base, pulled the power meter, and opened it up. The connections were all corroded, especially the neutral connection, probably from the salty atmosphere at the beach. The guy drove another grounding rod and connected the neutral to it, another violation of the code. The code says the only place the neutral is to be connected to earth ground is at the transformer (If you look in your electrical breaker panel, there are separate grounding and neutral bars and they are not supposed to be connected together). Well, it wasn't my house, but it did fix the getting shocked in the sink problem. That was truly weird.

Thanks Guest,

That's a very good down to earth (ground) explanation. I think I'll still lean toward caution though as SAIL4EVR alludes to. Good post.

John

The picture is cool John . Which way does the strike go though ?

Hiya Kris,

The lightning goes from "John" to "to" or maybe from 'to" to "John"? All depends on whether you're grounded or not.

Actually, it doesn't go any direction unless you're looking at it. It's sorta like: "this sentence is in Spanish when you're not looking at it".

Cheers

Aw John gimme more . I saw a nice program on lightning , mainly addressing the nature of lightning with high-speed cameras. I think the flash goes from ground to sky and then back , but I can't remember ! I was also being lazy and not doing a search on it. Do you (or anybody ) know the answer to this ? Kris

From what I have seen and remember the direction a lightning bolt travels depends on the sign of the charge within the cloud. However, generally there is a lower intensity path that spreads from the cloud down to the ground and then a massive surge that appears to propagate from the ground back up to the cloud. This is however only what one perceives and as with any electrical charge the actual flow is always from the negative to positive potential.

Lightning is also far more complex than most people realize and a single bolt is normally made up of several short duration bursts. This can cause problems as most lightning arresting systems can only protect you or the equipment from the first pulse and so the second and subsequent pulses inevitably cause damage.

Something else is the misconception that lightning never strikes in the same place twice. This is complete garbage and lightning will inevitably go for the shortest path to ground. Something else I have personally seen is a repeat bolt. I was filming a storm that was raging off the coast where I live and when I played the recording back I was astonished to see two bolts that were almost identical in position and shape. I checked and there were around 3 to 4 minutes apart and were surprisingly similar in shape size and position. I am not 100% sure of the mechanism here but clearly there was a preferred path through the atmosphere that the lightning was using for multiple discharges.

Finally there are more types of lightning that one might think. There are things called sprites, blue jets and elves that are highly energetic bolts of lightning that shoot upwards from the top of the clouds towards space. Little is know about these types of lightning and they have only be know to exist for less than 20 years, but, the make the more common type of cloud to cloud or cloud to ground lightning look like minor static discharges.

Hi masu,

Speaking of "other" forms of lightning such as sprites, blue jets, etc., have you ever heard of ball lightning? When I was a kid my grandmother used to tell us ghost stories and one of them was about a ball of fire that attached itself to their horse drawn wagon wheel one night (while they were riding in it). Now I realize this was told as a scary story for kids but I just wonder if it may have been based on some form of ball lightning that they saw. Ever heard of it or know anything about it?

"the direction a lightning bolt travels depends on the sign of the charge"

It's "up, up and away" if its sign is Aquarius.

John

Whoops, just found it at http://en.wikipedia.org/wiki/Ball_lightning

Gidday John,

I certainly have heard of ball lightning and I may have even seen it once, although, it was at a considerable distance and through a pair of binoculars so could have been any number of things.

One theory is that it is an electromagnetic wave that has caught its tail not that unlike an electron that is associated with the nucleus of an atom. Sort of quantum physics on a macro level. Another is that it is a ball of plasma that is generated by a lightning bolt and is held in place by some strange property of magnetic fields that we don't yet understand.

One of the real questions about lightning is what actually causes the ionized path that the lightning arcs through. While the voltages in lightning are astronomically high they are no where near the what you need to form an ionized path and cause a flash over. When scientists study lightning they give the lightning a path by firing rockets into cumulonimbus clouds that trail a thin copper wire behind them. The copper wire is what allows the ionized path to form and the lightning to discharge. The question is what natural event is doing the job of the copper wire?

There was a scientist doing a spectral analysis of lightning when he noticed that each bolt was preceded by a short burst of gamma radiation that appeared to come form outside the Earth. He postulated that the high energy photons in the gamma radiation were energetic enough to form an ionized path and allow the lightning to discharge. If that is the case then there are two prerequisites for lightning rather than one. I havn't heard any more on how he is getting on and whether he as finished his work but it's certainly interesting.

Lightning is a really unpredictable beast and trying to protect things from it is a hit and miss affair. The only guarantee when it comes to lightning suppression is that it's not going to work the way you thought it would. I have had a fair amount of experience with the damage lightning causes to electronic equipment and you can never guarantee to protect against it. Some years back I was working with a company that was installing an RS-422 communications network at the university I was working for. During the consultancy phase I stipulated a whole host of lightning arresting equipment and recommended that for inter building communications they go to the expense of using fiber optics. Management howled me down taking the word of the supplier that they had installed their system in numerous locations prone to lightning and had never once had lightning damage the equipment. Guess what, first thunderstorm and the lightning blew the crap out of the entire network, it was down for over 2 weeks while they replaced absolutely everything.. The only thing salvageable was the cabling, all the electronics was completely fried and beyond repair. You know I really enjoyed saying "I told you so" to the amoeba brained management that didn't listen to me. But, do you thing they learnt their lesson, no of course not. All they do now is have lots and lots of spares and replace the network each time it gats clobbered by lightning. Boy am I glad I don't work for that Mickey Mouse outfit any more.

Regardless of all this, we clearly do not fully understand lightning and there needs to be a lot of research done before we can even say we have witnessed every type of lightning let alone understand it.