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Daft plug wiring question

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  • 27-08-2020 6:31pm
    #1
    antix80
    Registered Users Posts: 2,419 ✭✭✭


    I'm asking this here so i don't have to demonstrate.

    What would happen if you wire neutral to neutral, live to earth, nothing to live, and plug it in.

    I'm guessing absolutely nothing, but have someone who reckons it would "blow the place sky high"


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    #2
    This is it
    Registered Users Posts: 5,554 ✭✭✭This is it


    Live from the device to the earth pin of a plug top and plugged into a socket, nothing will happen.


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    #3
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Depends what it is you connect to the plug. It can have an effect....


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    #4
    alan4cult
    Registered Users Posts: 1,583 ✭✭✭alan4cult


    RCD will trip, you've just connected live to earth.


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    #5
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    alan4cult wrote: »
    RCD will trip, you've just connected live to earth.

    He has just connected N to E via whatever appliance he connected this plug to.

    And depending on what the appliance is, it may trip the RCD, but only when a load is already connected, or added.

    If the OP connects a cfl across E and N of the plug, it is unlikely to have much effect.

    If however he connects a 3kw heater, now a N to E fault of about 17 ohms is introduced to the circuit. This may trip the RCD if a high enough load is on the sockets, particularly the one his incorrectly wired plug is plugged into.

    And he has to still say if he is going to connect the earth wire to the only remaining terminal in the plug:eek:, although he does say nothing connected to the Live/Phase pin.

    Answer to his actual question, will anything blow up, not in the way his friend thinks, no.


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    #6
    alan4cult
    Registered Users Posts: 1,583 ✭✭✭alan4cult


    OP said he connected live to earth as I read it no? This would trip the RCD.


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    #7
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    alan4cult wrote: »
    OP said he connected live to earth as I read it no? This would trip the RCD.

    I suppose it depends on how you look at it. But the OP said "nothing to live" which suggested they are talking about connecting the "live"(brown) wire to the earth pin.

    Maybe they will tell us if it was Live pin to earth wire, or earth pin to live wire they meant:D

    Anyway, if you connect the live plug pin to the appliance earth, the appliance earth/frame etc would be at phase potential, but would have to be in contact with something else to trip anything, or have an earth fault itself to trip anything. If it had an earth fault, it would trip anyway even if connected correctly.


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    #8
    antoinolachtnai
    Registered Users Posts: 9,807 ✭✭✭antoinolachtnai


    There are six ways to wire a three-pin plug. A surprising number of them will work (but only one is correct).


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    #9
    antix80
    Registered Users Posts: 2,419 ✭✭✭antix80


    Thanks folks.
    I'll tell you what it was. I was wiring a plug and put the blue wire to neutral. Some clown got excited and said "what way are you wiring that". I showed them and they went nuts and said (and i quote) "you'll blow the place sky high."

    Well, i said" what's wrong with it."

    This idiot said "you have the live to earth" and when i looked, because the live wasn't screwed in it looked like it was pointing up. Really, they just interrupted me when i was halfway through and probably scrambled for an excuse. So i thought I'd find out whether their reasoning held up.. And, it didnt.

    So, bit petty but I'll tell this chap to mind his own business.


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    #10
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    antoinolachtnai wrote: »
    There are six ways to wire a three-pin plug. A surprising number of them will work (but only one is correct).

    Probably only 2 ways will work unless there is either no rcd, or the load is less than 6.9 watts or so.


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    #11
    1874
    Registered Users Posts: 2,400 ✭✭✭1874


    alan4cult wrote: »
    OP said he connected live to earth as I read it no? This would trip the RCD.


    Live to earth,

    well, the live supply stops at the Live pin (in that set up) because it isnt connected to anything and voltage doesnt go anywhere, so I say, nothing would happen as you wouldnt get voltage at the device.
    (its almost equivalent to saying, what would happen if I didnt plug in the device, which would be nothing would happen).


    Now if the remaining earth wire was wired to the live (which seems more likely if incorrectly wiring something instead of leaving an unconnected wire in a plug) and that setup plugged in, I think it would blow the main fuse/trip the main breaker combination as current would flow directly to earth and Id say trip the RCD at the same time.


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    #12
    1874
    Registered Users Posts: 2,400 ✭✭✭1874


    I have a question that has been on my mind for years, Im of a mind to ask, so here goes
    Is there any reference between ground and the output of the secondary winding of a transformer?
    i.e

    Would current flow from the live wire to ground? as I dont think there is any reference to earth on the secondary winding?

    Obviously (to me) current will flow between one side of the secondary coil to the other.


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


    1874 wrote: »
    Live to earth,

    well, the live supply stops at the Live pin (in that set up) because it isnt connected to anything and voltage doesnt go anywhere, so I say, nothing would happen as you wouldnt get voltage at the device.
    (its almost equivalent to saying, what would happen if I didnt plug in the device, which would be nothing would happen).
    If a 3kw heater was connected in such a manor, it would be introducing a Neutral to Earth fault of around 18 ohms. This would change how the RCD operates with other loads, could cause trips, and also desensitizes it to phase to earth currents, as in, more than 30ma phase to earth would be needed to trip the RCD, as some of the return current would return on the neutral via the 18 ohm path, thus meaning more than 30ma shock current phase to cpc would be needed to trip it.
    Now if the remaining earth wire was wired to the live (which seems more likely if incorrectly wiring something instead of leaving an unconnected wire in a plug), I think it would blow the main fuse/trip the main breaker combination as current would flow directly to earth and Id say trip the RCD at the same time.
    If we take this example, again using a heater sitting on a laminated floor, plastic feet or wheels etc, earth wire in the flex connected to the phase (live), there is no path for the current to flow. The appliance frame is not connected to anything except the earth conductor in the flex, unless the appliance is making contact with something earthed, or has an earth fault already, in which case it would be tripping the RCD when connected correctly.

    I have an oil filled rad for example. It has plastic wheels. If I connect its earth wire in the flex to the phase, it will not trip anything while free standing.


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    #14
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    1874 wrote: »
    I have a question that has been on my mind for years, Im of a mind to ask, so here goes
    Is there any reference between ground and the output of the secondary winding of a transformer?
    i.e

    Would current flow from the live wire to ground? as I dont think there is any reference to earth on the secondary winding?

    Obviously (to me) current will flow between one side of the secondary coil to the other.

    There is no current flow if the secondary side is not earthed or neutralised. This is the principal behind shaving sockets. The output voltage is isolated. Only contact to the 2 pins would result in a shock.


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    #15
    1874
    Registered Users Posts: 2,400 ✭✭✭1874


    Bruthal wrote: »
    If a 3kw heater was connected in such a manor, it would be introducing a Neutral to Earth fault of around 18 ohms. This would change how the RCD operates with other loads, could cause trips, and also desensitizes it to phase to earth currents, as in, more than 30ma phase to earth would be needed to trip the RCD, as some of the return current would return on the neutral via the 18 ohm path, thus meaning more than 30ma shock current phase to cpc would be needed to trip it.


    If we take this example, again using a heater sitting on a laminated floor, plastic feet or wheels etc, earth wire in the flex connected to the phase (live), there is no path for the current to flow. The appliance frame is not connected to anything except the earth conductor in the flex, unless the appliance is making contact with something earthed, or has an earth fault already, in which case it would be tripping the RCD when connected correctly.

    I have an oil filled rad for example. It has plastic wheels. If I connect its earth wire in the flex to the phase, it will not trip anything while free standing.


    Not disputing it with you regarding the RCD, Its been a while since I did any calculations on fault current and Im not an electrician.
    That said if it was the only connection would it definitley trip? or might it be likely that it wouldnt trip, might have to be calculated (which you seem to have done in your example), again not disputing your reply, just interested to know as I didnt really write out explanations for myself of what I was being told when doing electrical theory, so dont think Id even understand my own notes AND its been a while.
    I thought that the RCD only measured faults across the live/neutral, if there was no current flowing, would this discrepancy exist to trip the RCD? you're saying yes? from Neutral to earth, but if there was no load?



    My other query is,

    He did say if he wired Live (phase)to earth, (as in the flex brown wire to earth, hence why I said nothing would happen) not sure if you misread that? or Im misundertsanding it. You seem to explain what would happen

    if earth wire in the flex connected to the phase (live), there is no path for the current to flow.
    I misread the description myself and was originally going to answer that the RCD would trip, but that even seems wrong, and you have explained that.



    Id have thought, how the OP described, nothing would happen.


    I get now what you're saying regarding a device earth wire to live insulated/isolated from ground wont do anything.
    I suppose unless someone touched the case of the device and was grounded themself.



    Bruthal wrote: »
    There is no current flow if the secondary side is not earthed or neutralised. This is the principal behind shaving sockets. The output voltage is isolated. Only contact to the 2 pins would result in a shock.


    A shock across 2 pins, yes, I thought so if contact was made with them, but still only for a sufficient voltage though, over 50 volts possibly.
    I was thinking 230volts but dont want anyone to try it out, but I essentially considered it would be possible to make contact with one wire on the output of the secondary side, not that Im going to try it, but I was convinced its possible.


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    #16
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    1874 wrote: »
    Not disputing it with you regarding the RCD, Its been a while since I did any calculations on fault current and Im not an electrician.
    That said if it was the only connection would it definitley trip? or might it be likely that it wouldnt trip, might have to be calculated (which you seem to have done in your example), again not disputing your reply, just interested to know as I didnt really write out explanations for myself of what I was being told when doing electrical theory, so dont think Id even understand my own notes AND its been a while.
    I thought that the RCD only measured faults across the live/neutral, if there was no current flowing, would this discrepancy exist to trip the RCD? you're saying yes? from Neutral to earth, but if there was no load?
    The RCD measures current out on the phase and back on the neutral. In simple terms, if there is a difference of 30ma or more, it is expected to trip. So if there is a fault from N to E in the socket circuit, and 10 amps flows in on the phase, and 9.5 amps returns on the N with the other 0.5 amps returning on the earth in the circuit via the link from N to earth, the RCD would trip.

    In the example of the 3kw heater connected to the N and E pins of the plug, this is an 18 ohm alternative path along with the Neutral itself. If the N path to the ESB meter was 0.1 ohms, this is 180 times lower than the 18 ohm path through the heater to the earth conductor (plus a possible 0.1 ohms for the earth wire itself if similar to the N conductor). So the return current on the circuit would split in a ratio of 180:1 to return to the point the N and E are connected together (neutralized point). So for 30ma to divert through the 180 ohm path, requires only around 6 amps in theory, to trip the RCD


    If there is a fault from N to E in the socket circuit, the RCD will only trip if there is current flowing. The nature of the fault and the distance out from the board determines how much load current is required to trip the RCD.
    If the load current is on a different circuit to the fault one, a higher load current would usually be needed to trip the sockets RCD then.



    My other query is,

    He did say if he wired Live (phase)to earth, (as in the flex brown wire to earth, hence why I said nothing would happen) not sure if you misread that? or Im misundertsanding it. You seem to explain what would happen

    if earth wire in the flex connected to the phase (live), there is no path for the current to flow.
    I misread the description myself and was originally going to answer that the RCD would trip, but that even seems wrong, and you have explained that.



    Id have thought, how the OP described, nothing would happen.


    I get now what you're saying regarding a device earth wire to live insulated/isolated from ground wont do anything.
    I suppose unless someone touched the case of the device and was grounded themself.
    Yes, thats about it, or if the metal frame was in contact with another earthed point, or the heater had a fault.



    A shock across 2 pins, yes, I thought so if contact was made with them, but still only for a sufficient voltage though, over 50 volts possibly.
    I was thinking 230volts but dont want anyone to try it out, but I essentially considered it would be possible to make contact with one wire on the output of the secondary side, not that Im going to try it, but I was convinced its possible.
    Contact with both pins would be required on isolated supplies.


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