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Thread: Bonding of Isolated Grounding system to plant electrode system, i.e. ground loop

  1. #21
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    Quote Originally Posted by Dale001289 View Post
    I just have to convince the client his idea is not a good one.
    Tell him that the way his system is set up is a ground loop, non code compliant, and when the link is lifted there will be nothing to clear a fault putting people in harms way.

    Roger
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  2. #22
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    I think I have enough ammo here to compose a 'tactful' email to the client telling him his proposed design is horrible.
    Thanks to all.


    Sent from my iPhone using Tapatalk

  3. #23
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    It has occurred to me that an EGC like conductor might not be an EGC if it is not intended to be used as part of a fault clearing path. For instance, if it was used solely to bond shields to earth, it would not be part of any fault clearing path.
    Bob

  4. #24
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    Quote Originally Posted by petersonra View Post
    It has occurred to me that an EGC like conductor might not be an EGC if it is not intended to be used as part of a fault clearing path. For instance, if it was used solely to bond shields to earth, it would not be part of any fault clearing path.
    Even if that were the case you would still be providing a loop for circulating currents in Dale's description of whats present.

    Roger
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  5. #25
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    Quote Originally Posted by roger View Post
    Even if that were the case you would still be providing a loop for circulating currents in Dale's description of whats present.

    Roger
    Where would the current path be if it is not connected to a power source?
    Bob

  6. #26
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    Quote Originally Posted by petersonra View Post
    Where would the current path be if it is not connected to a power source?
    In Dale's original post the conductor in question is connected to the GES, meaning it is an EGC in a loop back to the source.
    If we are going to shift gears from an "isolated ground system" to an "auxiliary GE", it is another conversation altogether.

    Roger
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  7. #27
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    Quote Originally Posted by petersonra View Post
    Where would the current path be if it is not connected to a power source?
    What wiring system is not connected to a power source?
    I will have achieved my life's goal if I die with a smile on my face.

  8. #28
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    Quote Originally Posted by Smart $ View Post
    What wiring system is not connected to a power source?
    If it is solely for instrument wiring shield grounding it is quite possible the shields never have any voltage on them, while the common side of the power supply running through the shielded cable might well be grounded.
    Bob

  9. #29
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    Quote Originally Posted by petersonra View Post
    If it is solely for instrument wiring shield grounding it is quite possible the shields never have any voltage on them, while the common side of the power supply running through the shielded cable might well be grounded.
    It is never the intention of any grounding conductor to have a voltage on it, be it shield or wire. But a voltage needs two points of reference and a potential between them. If you truly want the shielding isolated, just bond all the shields together and do not connect to ground (earth). But how do you propose to handle a 'line' to shield fault?
    I will have achieved my life's goal if I die with a smile on my face.

  10. #30
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    Quote Originally Posted by Smart $ View Post
    It is never the intention of any grounding conductor to have a voltage on it, be it shield or wire. But a voltage needs two points of reference and a potential between them. If you truly want the shielding isolated, just bond all the shields together and do not connect to ground (earth). But how do you propose to handle a 'line' to shield fault?

    The main concern here isn't exactly amps/voltage via the shielding, but rather several relative factors (electromagnetic induction, electrostatic coupling, or conduction), collectively known as EMI - Electromagnetic interference, i.e. "noise" feedback - into the DCS (or PLC) I/O, which controls plant operation. Specifically, regarding linear 4-20mA circuitry from critical, process-related transmitters, such as Flow, Temp, Pressure and Level.

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