Isolation transformer & Earth to Neutral

Discussion in 'General Electronics Chat' started by Mr.Smoke, Nov 19, 2013.

  1. Mr.Smoke

    Thread Starter Member

    May 26, 2006
    12
    0
    Dear All,

    We're facing a problem of voltage difference between Neutral and Earth. The power specialist recommended Isolation transformer for the job.

    We've just brought it, while wiring what actually he done is to connect input RST & Earth (separate) on the primary side and take output from secondary side.

    Then we checked E-N, the voltage was in Zeroes thus we connected a load on it. On load, the voltage between E-N shot-up to 17V. For resolving this problem he simply connected Earth with the Neutral of secondary side. Then showed us PD of 0.072 across E-N

    I am bit surprised about this practice, is it working really or it is just showing as connectivity? (2) is it Ok for the equipment?

    Kind response is requested,

    Thx
     
  2. Mr.Smoke

    Thread Starter Member

    May 26, 2006
    12
    0
    Rst = ryb (red yellow blue)
     
  3. passitherm

    New Member

    Nov 14, 2013
    2
    0
    Why not have the "protective ground" on the drawing right connect through to the E (earth) on the drawing left.?
     
  4. Mr.Smoke

    Thread Starter Member

    May 26, 2006
    12
    0
    sorry, didn't get
    pls clarify did you mean two separate grounds one one the primary side earth and other on the secondary side's neutral?
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,520
    2,369
    What kind of equipment is this and is the RST 3ph? and from what kind of secondary? RST and star neutral?
    You mention RST and separate earth, where is the earth originate and what is it connected to, you need to be a little more specific as to the details?
    Max.
     
  6. Mr.Smoke

    Thread Starter Member

    May 26, 2006
    12
    0
    Thx for your reply

    What kind of equipment is this and is the RST 3ph?
    Yes 3 phase, isolation transformer

    incoming connections: RST (or RYB it is just A,B,C or L1, L2, L3), E
    outgoing: RST (or RYB), N

    Powered guy, connected a junction between N(outgoing) & E (incoming) and showed us, no voltage across N & E. I'm trying to know whether it is really a practice in isolation transformer

    We are connecting isolation transformer to UPS, which supply 60kVA to CT-Scan through breakers

    and from what kind of secondary? RST and star neutral?
    I am unaware about it, i think it is just a normal isolation transformer which generate its own neutral & used primarily for safety purpose

    You mention RST and separate earth, where is the earth originate and what is it connected to, you need to be a little more specific as to the details?

    We made a separate earth for our system (CT), this earth is now connected to CT and isolation transformer (E) directly, and indirectly with N
     
  7. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    The way I look at the grounding is this: Primary side ground may be earth or some other point. Secondary side windings are both floating at the secondary potential; whatever it is. Grounding one side of the secondary to a chassis or other point leaves one side only at the secondary potential. If this was a boat, say, then only the high side will be a shock hazard, the grounded secondary will be at the hull potential (0).

    Cheers, DPW [ Everything has limitations...and I hate limitations.]
     
  8. Mr.Smoke

    Thread Starter Member

    May 26, 2006
    12
    0
    It means, we can do it.
    We can connect Neutral and Earth of isolation transformer to same Earth (separately made for the system)

    Thx
     
  9. killivolt

    Active Member

    Jan 10, 2010
    353
    311
    I would call a bonded Electrician if the equipment you have is expensive. I wouldn't chance it on if this or that, he will be able to varify Voltages, Amperages, and wiring.

    Don't call Jimmy the electrician down the street, call a Professional Bonded and insured Electrician. If they blow it up then at least you can get the money to replace it.
     
    Last edited: Nov 20, 2013
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,520
    2,369
    The connection of the 3ph star point secondary to ground is the normal practice, i.e. grounded neutral.
    BTW, this is the only place the neutral should contact earth ground, an exception is:
    If you connect, say a 1ph transformer across two phases then it is normal to re-reference one side of the secondary to earth ground right at the transformer, this now is a re-referenced neutral, for say 120vac control.
    Max.
     
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