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Confusing about grounding for regular AC-DC SMPS

Discussion in 'Power Electronics' started by az1024, Jan 14, 2019.

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  1. az1024


    Jan 14, 2019
    Hi folks!
    Please, check my logic. Here is well known schematic of usage AC-DC SMPS (for example, PC):
    L – phase wire, N – neutral wire, G – protective Earth.
    This scheme is actual for Europe. I don’t know how about US.

    I’m in confusing with three questions:
    1) Y-capacitors don’t works well – do not suppress symmetrical interference (suppress, but high-frequency only). And only one of them works in low-frequency.
    2) Shorts N to G cannot be detected by 1-pole circuit breaker. Returning current will flow thought shorts N+G.
    3) N-wire break cannot be detected. Power Supply will works on G-wire until it burn down.
    4) A vast of devices have direct connection between secondary (low-voltage) GND and G. What happens if G-path will has lower resistance than N? Power current will flow through G-wire, nor through N. The path of this current will unpredictable.

    Am I right?

    I’m not a native English speaker, please tell me in simple English. Thanks.
  2. duke37


    Jan 9, 2011
    Connecting neutral to earth is not permitted in the UK. If it does occur due to a fault, then a trip will actuate as sonn as there is a slight current, typically 30mA, running between them.

    What country has this system?
  3. az1024


    Jan 14, 2019
  4. Bluejets


    Oct 5, 2014
    MEN system.
    Australia for at least one.

    As far as "am I right" , I think some of your queries are "dreamed up" or at least "don't work like that".
  5. Minder


    Apr 24, 2015
    Looks correct to me, if the 3ph transformer using one phase and neutral is the service supply source, UK and elsewhere.
    The input filter is typical and desktop and tower PC's have the isolated PC SMPS supply referenced to earth GND via the DC common conductor.
  6. duke37


    Jan 9, 2011
    I mis-read the diagram.
    The supply to my house is PME which I think is phase, multiple earth where the 11kV transformer and all properties have the neutral conncted to earth.
    There was a fault in my father's house where the neutral was connected to the earth. This worked until sunday dinner was being cooked and the earth leakage trip would operate.
    My brother had a fault in the supply which meant that a steel building was 80V above true earth. The sheep being sheared did not like this.:( The fault was a leaky 11kV supply transformer allied with multiple only being one.
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