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equipotntial bonding

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    #32
    Armin_Tamzarian
    Closed Accounts Posts: 10,833 ✭✭✭✭Armin_Tamzarian


    robbie7730 wrote: »
    But no more current would be required to kill at 12v or 50v.

    But them voltages wont drive enough current to kill.

    If 50ma was the kill level, it wont make any difference what the supply voltage was that drove the 50ma current.
    So saying that at 230v, not much current is needed, the 230v part is irrelevant really.

    You're correct about the current but 230V was mentioned as that is what
    we are discussing.


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    #33
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Armin_Tamzarian wrote: »
    You're correct about the current but 230V was mentioned as that is what
    we are discussing.

    Yes but saying not much current is needed to kill at 230v makes it sound like a higher current is needed to kill if it was 150 volts.

    I suppose it is correct in a way what you are saying, as in the current required to kill is easily achievable at 230v.


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    #34
    Merch
    Closed Accounts Posts: 3,327 ✭✭✭Merch


    maybe its 30mA-80mA, Id have to check,

    goes to put finger in socket ;)
    After a quick check, less than 30mA it seems is likely not fatal (not 300mA as i said earlier)
    above it isn't helpful
    75ma Ventricular defibrillation
    above 100mA, life in danger

    so its 30-80ma not 300-800


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    #35
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Merch wrote: »
    maybe its 30mA-80mA, Id have to check,

    goes to put finger in socket ;)

    Yes that would be right. Somewhere around the 50ma is apparently the danger level.

    I tripped out RCD`s a couple of times myself through unintended conection of myself from live to earth direct:D


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    #36
    Armin_Tamzarian
    Closed Accounts Posts: 10,833 ✭✭✭✭Armin_Tamzarian


    robbie7730 wrote: »
    The way I always seen an earth rod on a tn-cs estate was, that it is another one added to the collective. More earth rods on the neutral of the estate, all connected together.

    The rod's we were talking about would be connected to the installation side, they do add to the collective but their impedance will always be much higher than that which comes with the supply.
    I guess you could call them a failsafe, under normal operation they achieve nothing really.
    I personally find it a bit excessive.


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    #37
    Armin_Tamzarian
    Closed Accounts Posts: 10,833 ✭✭✭✭Armin_Tamzarian


    robbie7730 wrote: »
    Yes but saying not much current is needed to kill at 230v makes it sound like a higher current is needed to kill if it was 150 volts.

    Fair enough point.


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    #38
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Armin_Tamzarian wrote: »
    The rod's we were talking about would be connected to the installation side, they do add to the collective but their impedance will always be much higher than that which comes with the supply.
    I guess you could call them a failsafe, under normal operation they achieve nothing really.
    I personally find it a bit excessive.

    Yes but as you add all the house connected earth rods together in a normal operating system, the overall impedance of the connection of the neutral system to the earth is quite low.

    This ensures a good reference between phases and earth throughout the system.


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    #39
    Merch
    Closed Accounts Posts: 3,327 ✭✭✭Merch


    robbie7730 wrote: »
    Yes that would be right. Somewhere around the 50ma is apparently the danger level.

    I tripped out RCD`s a couple of times myself through unintended conection of myself from live to earth direct:D

    1/20th of an amp?, it doesnt seem like much


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    #40
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Merch wrote: »
    1/20th of an amp?, it doesnt seem like much

    Yes it seems small alright.


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    #41
    Armin_Tamzarian
    Closed Accounts Posts: 10,833 ✭✭✭✭Armin_Tamzarian


    robbie7730 wrote: »
    Yes but as you add all the house connected earth rods together in a normal operating system, the overall impedance of the connection of the neutral system to the earth is quite low.

    This ensures a good reference between phases and earth throughout the system.

    No, that's right. I'm taking more about the installation side that loses the incoming earth.
    In that it only has those local ground rods left.
    They do their job but I just think it's a bit too much belt and braces.
    I've argued about this at length on UK installations, just out of technical curiosity.
    Let's say you provide a TN-S / TN-CS to a metal workshop.
    Most designers will insist on ground rods or a ring or something as a backup, basically.
    Nobody has ever been able to answer my question, where is the requirement for this in BS 7671 or BS 7430.
    The only place I agree with this is when the rods form part of a LPS.
    Then at least it's specified.
    For the sake of it, I can appreciate that's it's fair enough to bang in a rod, it'll do no harm and the cost is minimal, I just think it's done out of habit more than conformity.




    Merch wrote: »
    1/20th of an amp?, it doesnt seem like much

    No, I was surprised too.
    I used to think that the risk of shock went up the higher the current draw on the circuit you touched.
    Like a 63A circuit would be more likely to shock you than a 6A one.


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    #42
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Armin_Tamzarian wrote: »
    For the sake of it, I can appreciate that's it's fair enough to bang in a rod, it'll do no harm and the cost is minimal, I just think it's done out of habit more than conformity.
    Yea I discussed that very thing in here a few times myself. Or similar anyway. But as the circuits extend in an estate, the more earth rods the better.

    No, I was surprised too.
    I used to think that the risk of shock went up the higher the current draw on the circuit you touched.
    Like a 63A circuit would be more likely to shock you than a 6A one.

    Yes it has no bearing.

    The only extra danger is that the points that could be contacted are bigger. And short circuit flashes get bigger as the circuits do.


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    #43
    Armin_Tamzarian
    Closed Accounts Posts: 10,833 ✭✭✭✭Armin_Tamzarian


    robbie7730 wrote: »
    Yes it has no bearing.

    The only extra danger is that the points that could be contacted are bigger. And short circuit flashes get bigger as the circuits do.

    Yeah, you see I used to think that whatever the existing circuit current was, was what current you got shocked with.
    That if you touched a circuit that was, say, only supplying a table lamp, that your shock would be lower than if the circuit supplying your electric shower shocker you.
    Complete lack of understanding on my part, of how electricity flowed.
    Though, it is a widely misunderstood thing and to be fair, some of it is pretty difficult to get your head around.
    3-phase is a tough one to explain to a layman, usually.


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    #44
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Armin_Tamzarian wrote: »
    Yeah, you see I used to think that whatever the existing circuit current was, was what current you got shocked with.
    That if you touched a circuit that was, say, only supplying a table lamp, that your shock would be lower than if the circuit supplying your electric shower shocker you.
    Complete lack of understanding on my part, of how electricity flowed.
    Though, it is a widely misunderstood thing and to be fair, some of it is pretty difficult to get your head around.
    Lots of misconceptions out there alright.
    3-phase is a tough one to explain to a layman, usually.
    I dont believe in the rotating magnetic field myself, just the impression of rotation. I might be alone in that though.

    But yea, three phase is a tricky one for the layman.


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    #45
    Armin_Tamzarian
    Closed Accounts Posts: 10,833 ✭✭✭✭Armin_Tamzarian


    robbie7730 wrote: »
    Lots of misconceptions out there alright.

    Well, I think that the deeper you get into it, the more difficult it is to understand.
    When electricity was first introduced to Ireland it must have astounded some people.

    robbie7730 wrote: »
    I dont believe in the rotating magnetic field myself, just the impression of rotation.

    How do you mean?


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    #46
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Armin_Tamzarian wrote: »


    How do you mean?

    If there are 3 sets of windings in a 3 phase motor, each winding just has a sinusoidal current level in them, increasing and decreasing in sequence one after the other. So it is more 3 magnetic fields increasing to max then down to zero then max in the other direction, in sequence rather than a single field rotating.

    Maybe ive had too many now:D


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    #47
    Armin_Tamzarian
    Closed Accounts Posts: 10,833 ✭✭✭✭Armin_Tamzarian


    robbie7730 wrote: »
    If there are 3 sets of windings in a 3 phase motor, each winding just has a sinusoidal current level in them, increasing and decreasing in sequence one after the other. So it is more 3 magnetic fields increasing to max then down to zero then max in the other direction, in sequence rather than a single field rotating.

    Maybe ive had too many now:D

    I've had a few myself and I do find all that side a bit difficult.
    The 3 windings have varying phases.
    The phase angle varies with time.
    I honestly think that I don't completely understand all of the power generation stuff, it is hard enough to grasp.
    Took me quite a while to get how armatures are powered.


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    #48
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Armin_Tamzarian wrote: »
    I've had a few myself and I do find all that side a bit difficult.
    The 3 windings have varying phases.
    The phase angle varies with time.
    I honestly think that I don't completely understand all of the power generation stuff, it is hard enough to grasp.
    Took me quite a while to get how armatures are powered.

    If you think of the 3 windings as 3 sine waves. First one is at 400v rms. The next one will be 120 degrees further along its wave, and the next is another 120 degrees on.

    Its a sine wave by virtue of the generator rotor turning in a circular motion with its field rotating inside the 120 degree physically separated sets of windings in the stator.
    Here is a quick annimation I just found which would be like a motor. The 3 phase sine waves are to the right, and the magnetic fields increasing in sequence can be seen in the rotating diagram. The vector result of the magnetic fields is seen rotating.

    https://www.youtube.com/watch?v=eQk0OznWTjM


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