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Earth, Neutral swapped...curious

Discussion in 'Electrics UK' started by WideAreaNetwork, 12 Mar 2010.

  1. WideAreaNetwork

    WideAreaNetwork

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    Hi, I'm curious.

    I've just swapped a dual plug socket (standard UK 3 pin plugs) in my living room. Its one which is in constant use as it is where the TV plugs in. I found that the socket I removed had the Earth and Neutral swapped over. I am assuming this is unintended. The socket, as far as I am aware has been working fine. My question is - was this dangerous in any way? My fuse box is an old fuse wire one and I wonder if a newer style fuses would have detected this.

    Thanks for any replies!
     
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  3. 333rocky333

    333rocky333

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    A fuse or Mcb would not detect it.
    An RCD would have though
     
  4. RF Lighting

    RF Lighting

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    It could have been.

    As it is, you have been lucky. A fault on your installation could have been very dangerous.

    A new RCD protected type CU would have detected this fault
     
  5. kai

    kai

    Perhaps you have a PME supply, where the earth and neutral are joined together at the main service fuse block, just before the meter.

    If there is a green and yellow earthing conductor emerging from the side of the service fuse block, then you will very likely to be on a PME supply.

    It is Not correct, but it would have worked, as you don't apear to have an RCD protecting the installation.

    If the supply was a TT or even possibly a TNS, the performance of the TV or other sensitive electronic equipment may have been impaired somewhat.
     
  6. Paul_C

    Paul_C

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    If the resistance to earth with TN-S was high enough to impair the performance of the TV, it would be a pretty ineffective earth. Ineffective enough to be a danger in the event of a fault, since it would be unlikely to provide sufficient for sufficient fault current to operate protective devices.
     
  7. studentspark

    studentspark

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    So the earth is providing the neutral return path is that correct.
    I just presumed that without a neutral it would not work.

    I still don't get it though.
    eg. if i connected a light fitting and instead of live and neutral I connected live and earth would the earth act as a return path and effectively become the neutral.
     
  8. holmslaw

    holmslaw

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  10. studentspark

    studentspark

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    Sorry, but I am lost now. Where is the neutral return.

    For items to work you need a live and neutral, the earth is protective and does not provide function ?
     
  11. holmslaw

    holmslaw

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  12. Paul_C

    Paul_C

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    It is not intended to be a current-carrying path under normal operating conditions. But if you connect a load between L & E, it will become one.

    Take an old TN-S arrangement. You have L & N running from the transformer to the house, and the sheath of the cable is used as the protective earth. At the transformer, both the neutral and the cable sheath are connected to earth by an electrode, i.e. the neutral and the sheath are connected together. Normally, the sheath is used as the protective earth, and will carry current back to the transformer only in the event of a fault. However, if you connect a lamp or other load between the live and the cable sheath at the house, it will light, since as far as the electrons are concerned the sheath is just another metallic path back to the source of the power.

    With TN-C-S, you don't have a separate metallic path all the way back to the transformer, as N & E are bonded at the service entrance to the property. Again, the earths within the house are not intended to carry current under anything but fault conditions, but as they are all bonded to the incoming supply neutral, they will work as normal current-carrying conductors if you connect a load L to E.

    Finally, with TT there isn't a solid metallic path back to the transformer on the earth, but there will still be a path of somewhat higher resistance - There has to be such a path for the earth to provide its protective function. The transformer neutral is earthed, your installation is earthed to a local road, so you are likely to end up with an overall resistance over that path of a few tens of ohms to a few hundred ohms. You'll get a lamp or other load to light, but the resistance of the earth electrode connections in series with it will reduce the voltage across it - And cause the voltage of the installation's earthing system to rise. A modern TT system will have an RCD, so in practice this would not happen as the breaker would trip on what it (correctly) sees as an earth fault.
     
  13. Lectrician

    Lectrician

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    With a A TN-S or TN-C-S, you would not notice the fault.

    I once saw a TT install with no RCD. The light fitting in the kitchen had just been changed by the owner, and he had muddled N and E as the E was on the outside of the terminal block, not the middle has was expected. The impedance of the earth was such that the light fitting in the kitchen (halogen spots) worked, but dimmly. When on it also placed a rather nasty voltage onto all earthed metal work.

    We were involved because his plumber kept complaining of shocks while changing radiator valves.

    We traced the fault to the kitchen light fairly quickly. The owner said he knew it was dim, but had assumed it was how it was meant to be - it was in the early days of halogens, and he did not know what to expect.
     
  14. Adam_151

    Adam_151

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    I came across a domestic installation once that was TT, old VO-ELCB (which did not function), no bonding, and the earth conductor to the electrode seemed to be open circuit, occasionsal shocks from the sink were reported, open meggering before changing the DB I found something was down to earth, on investigation this turned out to be the 4-way extension for the television, dvd, video, etc having N and E transposed in the plug... just as well I make the point of meggering stuff at 250v first even when its just between live+neutral together and earth and only going to 500v if its clear... :LOL:

    EDIT: must have been some parallel path to earth somewhere (probably boiler) , becuase the TV worked fine... but did drag the potential on the MET up enough to make the homeowner wonder if they should wear rubber boots when doing the washing up :LOL:
     
  15. studentspark

    studentspark

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    excellent, interesting stuff and sorry for jumping in on your thread OP
     
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