Severity of electrical shock.

Discussion in 'Electricians' Talk' started by Jamesdod21345, Aug 20, 2017.

  1. Jamesdod21345

    Jamesdod21345 New Member

    How much greater would the severity of electrical shock be when a circuit has no load. EG ring main with nothing plugged in. Compared to a circuit with many different loads plugged into the circuit.

    (Edit) severity of electrical shock with fixed loads.
     
  2. MGW

    MGW Screwfix Select

    In the main no difference, there are however two types of electric shock, there is the shock when current goes through a metal part into your body, and there is when the atmosphere becomes ionised and the air conducts, this is normally started by a spark but can have explosive results causing people to be propelled many feet. The latter uses a lot of power and so having other items using the power so the overload activates sooner could affect it. Also of course if there is earth leakage on a circuit then the current required to trip the RCD can be reduced, however it takes just under 40 ms for an RCD to trip and until that time has gone you will get the same shock so RCD's do not stop you getting a shock they only reduce the time you get the shock for.
     
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  3. KIAB

    KIAB Super Member

    I qoute:

    There are three primary factors that affect the severity of a shock that a person receives when they’ve become part of an electrical circuit:

    1. The amount of current flowing through the body
    2. The path of the current flowing through the body, and
    3. The length of time the body is in the electrical circuit.
    4. The voltage of the current
    5. The addition of moisture into the environment
    6. The phase of the heart cycle when the shock occurs, and
    7. The general health of the person before the shock.
    In addition, the four other factors may affect the severity of the shock a person receives:

    And there are other factors affecting severity of electric shock, your body's resistance,it's lower in females than males, & age also plays a part.
     
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  4. unphased

    unphased Screwfix Select

    Its not a reasonable question to be asking, to be honest. Some shocks would kill, irrespective of the severity, others would burn or mame, others would just hurt and leave no after effects. Its pure luck what happens. There is no difference as far as I am aware to the outcome whether the circuit is loaded or not.
     
    seneca likes this.
  5. MGW

    MGW Screwfix Select

    I was very lucky, I had a new fridge/freezer so 22 years ago which needed a cold water feed, as it happened the loo was right above it, so micro bore pipe down the wall to a washing machine type tap, so lump of metal to space out two hack saw blades and slowly cut two parallel cuts the knock out plaster and fit pipe, quick test top and bottom no sign of cables.

    However it transpires some 30 years ago when the kitchen extension was built, the two way switches at the doors where not wired up to ceiling and then down to new switch, but horizontal around 4 corners to new switch, and I sawed through that cable, all house was RCD protected, so the RCD did trip, but with such good contact I ended up out for the count on the floor, still here 20 years latter to tell the tail, maybe if I had not been an electrician I would have tested for horizontal cables, but as an electrician I didn't expect anyone to run horizontal cables around a corner and around a pillar to the back door, without any conduit or trunking.

    Had the cable not been RCD protected likely I would be dead. I had a son would became a radio ham, and I had fitted two RCD's one for each fuse box old Wilex type now with MCB's in it back in 1991 at that time it was rare to have 30 mA protection never mind also on the lights, so had my son not passed his RAE at 16 I would not be here today.
     
  6. KIAB

    KIAB Super Member

    Like most trades, always expect the unexpected,dosen't surprise me horizontal cable runs, had it here for light drops & kitchen ring final & cooker cable was run diagonal down to the cooker outlet to mis a gas pipe.
     
  7. Bob Rathbone

    Bob Rathbone Screwfix Select

    The loading on the circuit will have no effect on the severity of an electric shock to persons or livestock. The important factors are.
    Voltage present
    Body resistance
    Effectiveness of ground or other conductor contact.
    The body resistance will be affected by the presence of water, such as on building sites, swimming pools home hot tubs.
    The effectiveness of ground contact will be affected if the person is in a confined space surrounded by conductive earthed metal, such as in a duct or pipeline.
    The physical condition of the victim will also play a significant role in the outcome as will the time the victim remains in contact with the supply and the delay in receiving appropriate emergency treatment.
    Good outcomes will be found with fit victims with a high body and contact resistance who have been in contact with lower voltage supply for a short time, much less than a second, and have received prompt appropriate aftercare.
     
  8. retiredsparks

    retiredsparks Super Member

  9. JP.

    JP. Screwfix Select

    Lec and Un doing a job together - .Un's doing the switch and Lecs holding the torch..:)
     
    Last edited: Aug 20, 2017
  10. spinlondon

    spinlondon Screwfix Select

    Must admit, have always thought the shock is greater when there are loads to when there aren't.
    Not actually done a comparison though.
     
  11. sospan

    sospan Screwfix Select

    The worst electrical shock i have ever had was from static . I ended up with a burn on my hand and a few bumps and bruises but the other guy whom was a few feet away ended up worse than me, he saw the flash, a load bang and me flying backwards, landing unconscious on the floor. However, when assistance arrived he was standing there motionless absolutely rigid and never saw him again.

    Nearly 30 years later, static still very wary of static build up
     
  12. JP.

    JP. Screwfix Select

    The worst shock I got which was many years ago was from an old crt colour tv. I had the back off (it was unplugged) and I started peeling back the rubber flap which surrounded the anode connection on the tube. I peeled it back what some 25mm and all of a sudden there was a loud crack of electricity and it wacked me right up the arm - never ever felt anything like that before, and never took backs off crt tv's again. Should have used an earthed lead to discharge the anode first, but didn't do that and that is what happened. You certainly learn respect for stuff like that, thats for sure.
     
  13. seneca

    seneca Screwfix Select

    That does wake you up a bit doesn't it JP! Had a few of those over the 40 years I spent as a TV engineer, the final anode runs at around 25kV, and when the set is switched off the eht reservoir capacitor, which is formed by the external graphite coating and the internal similar coating can hold a charge for quite a while. High voltage of course but not really dangerous as only microamps involved.
     
  14. btiw2

    btiw2 Screwfix Select

    I think the answer partly depends on why you want to know.
    If you're curious about how it works in practice then the answers above pretty much sum it up. I.e. best not find out eh? Oh yeah, make sure you have RCDs!

    But this is your first post. So I don't know what sort of an answer you're after.
    If this is a physics homework question (i.e. purely theoretical and the real world doesn't gets a look-in) then you probably want to point out in your answer:

    Sockets are in parallel. e.g. Your kettle doesn't get weaker because you turn the microwave on.
    Thinking about it, sockets in series would be weird. You'd need to turn the microwave on to even use the kettle.
    i.e. if you've decided to bypass the protection on your plug socket and wire yourself into the mains then, no, I don't think the other loads would make a difference.
    I suppose you could argue that if there were lots of other loads the additional current you'd draw could blow the fuse (I'm assuming no RCD).
    In practice I think you'd be thrown across the room before the fuse noticed, and you'd probably draw less than an amp[1] anyway.

    If there were a fault in a device under load and you got involved in the circuit at the device itself then it'd depend on how you were arranged in the circuit[2].
    If you had a high impedance[3] and you were in parallel with the device then some of the current will still be going through the device (depending on your resistance vs the device's).
    I suppose that's (slightly) better than having the full voltage across you, whereas if the device was off then you'd take the full whack because you're the only route that the current can take.

    [1] An amp? I don't know the resistance of a person - but I doubt it's below 240 ohms... or could be, if you were wet? Dunno. Google it.
    [2] Which wouldn't actually be a circuit any more - but you know what I mean.
    [3] Which I'm going to carry on calling resistance because I'm not a sparky and I don't care.
     
  15. Dr Bodgit

    Dr Bodgit Super Member

    What kills you is current, and what determines current is a combination of:
    - the voltage;
    - resistance (or impedance more precisely);
    - the amount of energy available in the power source.

    The amount of current needed to kill is I think around the order of 100mA or so, which is why RCD protection kicks in at 30mA.

    Lets say the human body has a resistance of 1000 ohms (I goggled that) then current = V/R = 230/1000 = 230mA. So mains electricity will probably kill you. The main factor here is the voltage and unlimited energy available (roughly speaking).

    Static is different, the voltage is a lot higher but there is limited energy available. That's why you only get a shock from static electricity and it doesn't kill you (most of the time).

    Whether an appliance is plugged in and operating on the same circuit you put your finger on will make no difference what so ever.
     
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  16. btiw2

    btiw2 Screwfix Select

    Yes, you're right.

    Thinking about it again.

    This bit:
    is nonsense.

    If you were in parallel with the device then there'd still be mains voltage across you to ground regardless of what the device was doing.
    I.e. you're getting equally fried either way.
     
  17. Dr Bodgit

    Dr Bodgit Super Member

    I think the OPs post should have referred to touching the "return" side of a live appliance. Then you have the combined resistance of the appliance plus the human body. The appliance resistance won't be much but it will reduce the shock a bit

    [Although the neutral will be very close to earth won't it...so the shock might not be much at all]
     
  18. MGW

    MGW Screwfix Select

    I suppose a shock from a shared neutral would vary according to what was plugged in.

    As to current or voltage giving the shock, back as an apprentice I found if you hold the wires from a wind up mega tight you don't get too much of a shock, so I asked the first year apprentice to hold the wires on for me, he had an idea what was going on so refused, I held the wires tight, he wound the handle while watching my face, yes little tingle but not much, he then satisfied that he would not get the shock, held on the wires, lightly however, so one turn of handle and he got a right belt.

    So I would have had more current through my body, but less volts, so in practice it is clearly the volts that make you feel the electric shock.

    Latter on sent to a motor vehicle workshop, I noted an impulse mag mounted under the bench, right I thought I'll teach him a lesson, so chatted leaning on the vice, as I saw his hand go down I put my two fingers on the back of his neck, that was the last time I ever tried giving some one a shock, he fell to the floor, and it seemed for an age was motionless, he very slowly recovered, I was congratulated by rest of workshop, seems he had given everyone a shock or two, however I thought I had killed him, I was extremely worried until he recovered.

    As a kid I had put bits of wire between an electric fence and normal fence and thought if very funny when the farmer got a shock, but now I realise how daft it was.
     
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  19. That doesn't seem to make sense to me. If you held the contacts firmly, then the resistance of the contact points would be reduced - so a greater current would flow through you = larger 'shock'. It would certainly be the case if touching a mains live wire.

    Could it be that, by gripping tightly, you were tensing your muscles and the current therefore wasn't able to 'spasm' you as much? Also, you were anticipating the 'belt' and were ready to accept it, whereas your victim was anticipating something worse - like the intense fear of being tickled...

    Where I were a wee lad, I had an uncle who constantly tinkered with his cars. I was visiting one day as he was under the bonnet, engine running, and he called me over to see what he was working on. Thankfully I noticed as he 'secretly' removed a spark plug cap, clutched it firmly in one hand and reached out to me with the other as I approached. What a bar steward :).
     
    Last edited by a moderator: Aug 22, 2017
  20. I think the neutral is effectively at earth potential, so you shouldn't get a shock at all if touching it? Unless it's faulty.

    Isn't the neutral actually 'earthed' on some systems?
     

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