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Electrical Wiring ?

Discussion in 'Electronic Basics' started by [email protected], Nov 9, 2006.

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  1. Guest

    I repaired a hot water supply unit which is run by 3- phase 440 volts
    ac ( no neutral ).
    There is a step down to 220 volts tranformer inside the control panal
    which also control other switch gear like, temp. controller, contactor.

    Surprisingly one of the 220 volt terminal was earth, my earth leak
    circuit breaker did not trip.
    My concens is this safe ? Dear members can you help me in this
    question. Thanks

  2. Phil Allison

    Phil Allison Guest

    ** Groper Alert !

    ** Why should it ?

    The step down transformer provides "galvanic" isolation for the 220 volt
    secondary - so it can be connected ( at one end) to any thing you like,
    including earth.

    ** Long as you don't touch the 220 volts terminal - yes.

    ........ Phil
  3. An earth leak (ground fault) breaker trips on ground current
    above some limit. This happens when a circuit is completed
    through ground. This takes two ground connections, one
    where the current enters ground and one where it comes back
    out to the voltage source. If your 220 is produced by an
    isolated transformer winding, it has no earth connection.
    You can ground one side of that winding to define the
    voltage on the other end of the winding with respect to
    ground. This is called neutralling the secondary. If the
    440 passes through a ground fault breaker, and is also
    neutralled somewhere up stream, and the 440 to 220 step down
    transformer developed an insulation fault, there would be a
    ground fault circuit completed (ground would be a current
    path between the two places it was connected to the 440 volt
    source) and the ground fault breaker would trip off. Also,
    if the 220 volt hot line developed any leakage path to
    ground through any of the control devices or wiring, there
    would be two connections to ground across the 220 volt
    winding, and, if the ground fault breaker was installed on
    the 220 volt pair, this ground current would trip the
    breaker off. In effect the second ground connection would
    detour some of the line current from the hot side back to
    the transformer through the two ground connections (the
    fault and the neutral connection). The ground fault breaker
    detects that there is a difference between the current going
    one way in the hot line than is returning through the
    neutral line, and concludes that current most be escaping
    through some additional ground connection, and trips off.
  4. Guest

    Thanks Members for the prompt response, appreciate it, thanks! .
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