Electricity kills! As if you didn't already know.

By Percydood ยท 16 replies
Mar 2, 2005
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  1. One of the threads I was on got a bit distracted and I was asked to start a new thread to find the answer to this.

    Here's a poser for all of you. Let's say you are sat in a plastic bath (tub) full of soapy water. You are sat at one end away from any earths and some evil person drops an electric fire or other electrical appliance in the other end. Electricity takes the shortest route which, assuming the appliance is not earthed would be from the live terminal to the neutral terminal. If this is true, why are you at risk of death from electric shock? I have an explanation but no-one has ever categorically explained this and I would like your opinions.

  2. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    Where did that "at risk of death" claim come from if you are not sure and noone has any facts?
    We are constantly at risk of death from anything. It's all about odds anyway.

    Inspired by that runaway thread I tried looking up some things on the net (looks like that your poser is not too original of a subject in forums) and all the places I bothered to look came up with a result of "probably won't kill you".

    Any why the silly provocative tone in your post?
    No need to shout. If you have a theory then present it. If you have a question then ask it.
    And if somone actually tries this and dies - it's a favour to evolution.
  3. Percydood

    Percydood TS Rookie Topic Starter

    Why shouldn't I suggest that an act could have fatal results? You contradict yourself suggesting that I shouldn't say that a person may be at risk of death and then say that we are all at risk of death. Very odd. And to suggest that I can shout using text is ludicrous. It may surprise you that using capital letters is a way of drawing attention to an important statement. It does not suggest I have raised my voice.

    Quite rightly, it was suggested that the thread had got distracted and perhaps I should post it under a seperate heading which I have done. I don't understand why a simple question should sound provocative. It's a bit of an odd thing to say as well since you clearly are being provocative in your text given that you 'bothered' to look it up on the internet. I thought I'd found a website where questions could be asked without anyone being childish and I am stunned to find that a member who is considered a 'TechSpot Chancellor' is quite aggressive in their reply. If you don't like my question, don't answer it.

    And as it happens, as I mentioned in my post, I do have an answer and I was interested in other peoples technical and educated answers. It seems that it is not possible to ask a simple question without someone getting angry about it. Try doing that in the real world and not this anonymous, virtual world.

    Despite my post, this is not a place to argue and since you are likely to reply with something else aggressive following this, I shall not invlove myself with this website anymore, much to your pleasure I am sure.

    As for the favour to evolution, perhaps you should try and resolve this. Next time you are in the bath.....
  4. PFJ

    PFJ TS Enthusiast Posts: 112

    I hope you do return Percydood - if not this reply will be lost to the aether or wherever unread replies end up. Also I am interested in the answer and perhaps a sensible, logical and friendly discourse on the subject.

    I did ponder the question as I have in the past. It would seem strange that the person in the bath would be electrocuted because electricity follows the path of least resistance - to the ground or between live and return/neutral or to the taps.

    I can only pose that there is a chemical change at molecular level because of the 'soapy water' (mayhap therein lies your clue) perhaps or salts due to perspiration of the bather (I'd perspire if I was being electricuted). So does the water itself become a pond of conductivity?

    Or is it a trick question? Perhaps the bather has a very good trip switch (ELCB) and survived.

    If you do return, and I hope you do, perhaps you would be kind to offer your explanation please.
  5. SNGX1275

    SNGX1275 TS Forces Special Posts: 10,742   +421

    I do not know the true answer, but I think the analogies on this page may contain some insight: http://www.physicsforums.com/archive/t-62288_a_toaster_and_a_bath.html

    My bet is the analogy some dude said about pouring water in a sink, eventually it will all go down, if its poured too fast it spreads out since it all can't fit down the drain at once.
  6. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

    You can suggest whatever you want, but you have to be able to back it up.
    With the kind of proof you are offering I might as well claim that a giant furry purple elephant will appear on your desk tomorrow. It could happen thanks to quantum physics but the odds are unrealistic.
    It is widely known in the online community and also mentioned in TS forums guidelines (you did read those?) that text in all capitals is shouting. We use bold to emphasise things in a civil way.
    Nothing wrong with your question..
    But the thread title actually makes a statement.
    Then you say you actually don't know anything.
    Then you ask a question.
    And then you say that you have an answer but you won't tell and you are expecting everyone else to post instead.
    I don't quite see what my status label on these forums has got to do with anything. Why do you think I would fail to see other peoples shortcomings and be nicer myself if my status was anything else.
    And if you don't like my answers, don't read them.
    Telling someone that you have an answer to a complicated problem, but you are expecting the others to make their (wrong) guesses first while you giggle away in your safe position.. That's real nice.
    Thank you for being so unchildish.
  7. Spike

    Spike TS Evangelist Posts: 2,168

    the answer to this is simple.

    If the bath has a path to earth hat isn't insulated from the water, like the taps or plug hole, you're at risk.

    If there's no path to earth and you're lying in the bath, and along comes a live electrical device, you're smiling. It's when you touch the metal taps or srep out of the bath that you start frowning.

    If the bathwater itself isn't insulted from earth, then there's a arisk from the force of the initial electrical surge as it spreads through the water.

    If you drop an electrical appliance in one end of the bath, as the charge equalises through the water, the voltage at the appliance end will be higher than at the other end of the bath, thus creating a potential difference, and so allowing acurrent flow. It's the current that kils you with electricity, not the voltage. This may only be for fractions of a second, but if the current is high enough, then fractions of a second is all it needs.

    The same thing applies to lighning strikes. The old advice of getting down on all fours to avoid being killed by lightning is bad advice. It's safer to crouch on two feet. This is because when ligning hits the ground, the voltage radiates out like ripples in a pond, getting weaker as it goes, and so creating a potential difference. If the drop is sufficient between where your hands are, and where your knees are, you're going to get hurt.

    The truth is, in a bath, there's no way to be sure, and so the safest thing to do is not thake your electric fire to the bathroom with you, to bath alone, and lock the door if you thing someone might want to drop an electric heater on you for some reason or other.
  8. Percydood

    Percydood TS Rookie Topic Starter


    "Despite my post, this is not a place to argue and since you are likely to reply with something else aggressive...."

    ...like I said.

    To everyone else.

    In answer to my question, Spike is correct. Assuming that the water has less charge than that of the electrical appliance being dropped in and it will have considering the water will have come out of an earthed pipe, the electricity will form a field across the water until the water becomes charged. The potential difference from one side of the field to the other can be significant and with wet skin being quite a good conductor (relatively speaking) the potential difference from your feet to your back (assuming you are sat in the bath) could be enough to electrocute you. Exactly what happens there and how a person may die depends on the circumstances. The body would convulse which could lead to drowning etc, etc.

    This effect is similar to a broken power line touching the ground. Again, a field is produced while the current travels mainly to earth around the area of the conductor. Stand with your feet together to ensure the smallest potential difference. Cows have no chance!!

    As for the soap, well, you have to keep clean!!

    Soapy water may well contain salts and other deposits which contaminate the water and make it a better conductor.
  9. PFJ

    PFJ TS Enthusiast Posts: 112

    Isn't it nice to share :) . Now I'm a little bit more educated then I was yesterday and isn't thats what it's all about - shareing acquired knowledge (in a friendly manner of course) as Techspotters.

    That probably concludes this thread unless others have knowledge to impart or argue other points of view. Spike als explained it well - good work.

    Nice to have you back Percydood.
  10. Spike

    Spike TS Evangelist Posts: 2,168


    not nessecarily. It depends on the resistance and temperature of the water, and the voltage and current of the electricity, not to mention the the amount of charge availiable, what protection is available in the house in terms of earth leakage detectors/fuses/residual current detectors, etc.

    It's worth remembering, if you're going to think about this, that... ...the current is proportional to the voltage, whilst inversely proportional to the resistance, PROVIDED THAT the temperature and all other constants remain the same. - Ohms Law.

    Incidentally, it doesn't take much current at all to kill you, and wouldn't nessecarily cause convultions. I'll see if I can find a table later somewhere from google with the values and effects of electrical current.

    That said, personally, I thought that the best advice in my post was...

    The truth is, in a bath, there's no way to be sure, and so the safest thing to do is not thake your electric fire to the bathroom with you, to bath alone, and lock the door if you thing someone might want to drop an electric heater on you for some reason or other.

    ... that way you don't have to worry about the soap :)
  11. Percydood

    Percydood TS Rookie Topic Starter

    While I agree Spike, I would imagine that dropping a 240 appliance (UK) that is not earthed into a bath of mineral rich water which is also not earthed (plastic drain pipe), there will almost certainly be time enough for the field to charge the water sufficiently before the supply breaker was able to blow. Remember, that a 30 amp breaker will maintain 30 amps for some time, and may not even trip at all at this current. Breakers, like fuses, will probably require a significantly higher current than it's rating in the form of a transient since they have to account for inrush currents. Breakers are designed to protect the appliance wiring and not the operator, which of course is why earth trips are used and will trip at around 30mA. This is still enough to kill you if the current is across the heart though. I'm not sure how much difference there is in the resistance between hot water and cold water. I imagine that, like wire, resistance increases with temperature, reducing overall current but I would think that it wouldn't be more than a few ohms per metre. Interesting point though. It might be worth getting a plastic bowl, multimeter and some soapy water and seeing if this does actually work. :rolleyes:
  12. Spike

    Spike TS Evangelist Posts: 2,168

    I disagree.

    Most breakers these days in the UK are RCD's (Residual Current Detectors), particularly in newr homes. These ARE designed to protect both the istallation and the operator.

    Instead of detecting the earth leakage of a system (thus indicating a fault), or measuring resistance (thermal protection like a fuse - heat increases with current and resistance.), RCD's detect the residual current between live and neutral and trip at very low values, and so on a RCD protected ring mains, dependant on the system values, dropping an appliance in water would produce a live/neutral short, which would trip out the power almost instantaneously. This is in much the same way that RCD's often trip out when lightbulb wear out and blow.
  13. Spike

    Spike TS Evangelist Posts: 2,168

    Here it is.... ...a list of effects on the human body of electrical shock, and the current required for your average person....

    taken from...

    It should be noted that tissue burns start at around 200 mA

    It should also be noted that I have no idea what frequency these values are typical of, and that Ventricular fibrilation can in some cases start even as low as 30 mA. The human body is most suceptably to AC current electrocution when the frquency is between 50 Hz and 60 Hz. Co-incidetally, mains frequency in the UK is 50 Hz
  14. Percydood

    Percydood TS Rookie Topic Starter

    Do earth trips work in a similar way? As I understand it, they measure the current in both the live and the neutral and they should be the same, current in a series circuit is the same at all points, and so if there is a difference, it must be going somewhere else, probably earth and maybe a person. This is unlike the older detectors which actually measured the current in the earth. That way an earth trip can trip at a much lower current.

    Clearly you have some more experience than I do. It's been a long time since I have been involved in domestic electrical protection.

    Also, it is interesting that the human body is most susceptible to AC electric shock at those frequencies. I did hear that, when the power grid was being designed, there were two trains of thought. Someone was developing low voltage DC and the other, high voltage AC. In order to demonstrate that high voltage AC was incredibly dangerous, the other guy invented the electric chair!! Do you know if this is true? :confused:
  15. Nodsu

    Nodsu TS Rookie Posts: 5,837   +6

  16. Spike

    Spike TS Evangelist Posts: 2,168

    I don't know if the electric chair thing is true. lol

    DC current is also very dangerous at high levels, but is far less efficien in transferal from generation to supply.

    The two types of protection you are thinking about are ELCB (earth leakage circuit breakers) and RCD, and you seem to have the two confused.

    NO ELCB detects residual current, and no RCD detects earth leakage. ELCB simply detects a current in the earth and breaks the live when it trips out.

    Both have their flaws though. :)
  17. tbab

    tbab TS Rookie

    excelent reply :hotouch: :hotouch:

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