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Thread: Wiring a Home DB with 2 phases

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    Lightbulb Wiring a Home DB with 2 phases

    Hi All,

    I recently had an electrical issue where the live and neutral shorted out at the pole outside the house and it got me digging a little deeper in to my home DB.
    I'm no electrician, but I have a pretty good understanding of how wires should be and I like to know exactly what's happening in my house considering it's an investment.

    I have a pretty old house, that has two phases coming in and a neutral.

    Currently the Main DP switch breaks these two phases and then the neutral goes straight to the Earth Leakage.
    From what it looks like, one phase goes to the Earth Leakage, the second goes to the Light Arrester.

    The Earth Leakage phase (P1) then provides power to the plugs in the household and the Light Arrester phase (P2) provides power to the lights, geyser, stove and Sub DB (Gate/Garage).

    This seems a little off to me, but as I said, I'm no expert here.

    Should I be getting a 3 Pole Main Switch to break both phases and the N?
    Should I have a Leakage Switch for each phase individually?

    Of course I'll be pulling in my electrician to do all the wiring correctly, but I'd just like to understand how it all should work as well.

    Thanks in advance,
    Cheers

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    I have yet to come across a 2 phase supply to a house. It's either single or 3 phase. What council meter do you have ? Single or 3 phase ?

    Derek

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    It's a 3 Phase meter.

    Definitely only two phases and a neutral coming in

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    Diamond Member AndyD's Avatar
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    Can you post a couple of pictures maybe?
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    Hi

    I have come across 2 phase and neutral supplies in older areas .Was a common type of supply in the " old Days" . The book is written to accommodate such instances and hence the reason they refer to as multi phase.
    It is no longer common practice and normal is defined in the Regs as a 5 wire supply.

    You do not need to disconnect the neutral in a multiphase supply subject to 6.9.2.2 and it has only been in the last 4 or so years that an earth leakage is required for a geyser circuit.
    So , no , one earth leakage on plugs only was fine but in the same breathe depends what was in the garage DB .

    6.9.2.2 In the case of a single-phase circuit, the disconnecting device shall
    disconnect live and neutral. In the case of a multiphase circuit, the
    disconnecting device shall disconnect all the phase conductors but need not
    disconnect the neutral conductor in an installation
    connected to a supply
    system in which the neutral conductor is earthed direct (see the TN system in
    annex K).

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    Thanks GCE.

    It is quite an old house, happy to see that it's not out of the ordinary wiring.
    The Garage DB is just lighting in the out houses, the door itself is manual.

    Out of curiosity though, doesn't a Main Switch Trip when it picks up an issue with the Neutral and the Phase? If it's wired only on the phases then does that job now fall to the Earth Leakage?
    And what should then protect the lights, geyser, stove etc on the phase that isn't connected to the Earth Leakage?

    Also, I really have no idea what a surge arrester is supposed to do, does it just shove power down the Earth cable when the Voltage is too high?

    Thanks again,

    PS Picture posted for interests sake
    Click image for larger version. 

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    Diamond Member Justloadit's Avatar
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    A surge arrester clamps the supply line to Neutral/Earth depending on how it is wired or type, if there is a voltage that exceeds a reference point.
    Usually 1000V. The surge arrester relies on the circuit breaker/ELU to disconnect the load to prevent damage.
    What one needs to understand, is that the surge arrester must absorb the energy of the surge, and in some cases will short circuit itself while protecting the load. In the case that the energy is within the surge arresters capability, it will still hurt the arrester, and in time as further surges are absorbed, it will short circuit itself.

    Due to the short circuit effect of the surge arresters, which could cause a fire, legislation has now demanded, that special thermal fuses are assembled with in the surge arrester housing. To allow users to know if the surge arrester is still operational. either an LED or Neon lamp is used. If the indicator is on, then the surge arrester is still in operational condition. If the indicator is off, then to maintain protection, it should be replaced ASAP.

    Good quality surge arresters are not cheap, but then again not having one does cause much high damage cost.
    The idea is that the more surge arresters are installed in the supply lines, the better overall protection is achieved, as the surge is then shared between all surge arresters connected to the lines.

    Usually what happens is the the first person who installs a surge arrester in their DB box, has many 'failures' of the surge arrester, as this one surge arrester is protecting the whole network. As more users install surge arresters, so less 'failure" of surge arresters occur, and better protection of the network.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar pumping, Solar Geyser & Solar Security lighting solutions - www.microsolve.co.za

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    Cheers man, thanks for the info.

    I think I'm ready to have a look at NOT blowing things up.

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