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Thread: Ungrounded 480x240 delta to delta 3ph 3w voltage to ground reading

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    Ungrounded 480x240 delta to delta 3ph 3w voltage to ground reading

    Need clarification / conformation on the voltage readings to ground, and suggestions / solutions.

    Knowing the secondary 240 line to line should be 240v and line to ground should be 0v.
    Found a voltage reading to ground on a disconnect and was able to determine the circuit that was causing the fault.
    Removed the wiring from both the disconnect and wiring to the circuit breaker at the panel board and locked out both. Have not been able to troubleshoot further at this time.

    Now another disconnect is reading to ground. I am not able to secure this circuit, and know this needs to be addressed before another fault may occur. Can someone explain what may occur if this is not repaired or resolved.

    The location has an old CH V48M24T12F is a Delta to Delta transformer. Eaton’s tech support sent me this “Since this transformer does not create a neutral there is nothing to ground and the 240 VAC does not have a reference to ground and you should not see voltage to ground, only line to line.”

    I am suggesting the ungrounded transformer be replaced with a grounded system.

    Thank you,
    Robert

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    Just to clarify:
    The secondary is 240D, ungrounded?

    If it is, then this is not right:
    “Since this transformer does not create a neutral there is nothing to ground and the 240 VAC does not have a reference to ground and you should not see voltage to ground, only line to line.”
    Without data you’re just another person with an opinion – Edwards Deming

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    yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings

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    Quote Originally Posted by killer76 View Post
    yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings
    Since the 240D is ungrounded, then the phase to ground voltage is undefined. It can be about anything (between 240V and 0V). One can usually measure something because of capacitive coupling. If the coupling is perfect balanced, the phase to ground voltage would be 139V = 240/(sqrt(3)

    If you are reading phase to ground of:
    240V
    240V
    0V
    that is telling you that you one phase has an unintentional ground.

    Before I suggested changing to a grounded system, suggest checking why the existing is ungrounded, and the requirement of the existing loads. Some loads may not be happy with some types of grounded systems.
    Without data you’re just another person with an opinion – Edwards Deming

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    Quote Originally Posted by killer76 View Post
    yes that is correct only, there is only a ground bolt to the case inside the transformer nothing to the windings
    There should be ground detectors - Could be as little as three incandescing light bulbs.
    Without data you’re just another person with an opinion – Edwards Deming

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    the only loads are to single phase and three phase receptacles for welding machines and a couple plasma cutters, fused disconnects feed the receptacles.

    going to get the measurements from the disconnects when no load in present.

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    was told that using digital volt meter will give different readings compared to the wiggy type meter, i have an Ideal Vol-Con tester and digital UEI and will use both.
    I was asked to see if you can you give a little more on the ground detectors - Could be as little as three incandescence light bulbs. How would they be connected
    any advice or suggestions are greatly appreciated

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    Ive seen systems as simple as lights connected in series between phases and ground or you can get more "professional"
    http://www.directindustry.com/prod/e...3-1690990.html
    At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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    Quote Originally Posted by killer76 View Post
    was told that using digital volt meter will give different readings compared to the wiggy type meter, i have an Ideal Vol-Con tester and digital UEI and will use both.
    I was asked to see if you can you give a little more on the ground detectors - Could be as little as three incandescence light bulbs. How would they be connected
    any advice or suggestions are greatly appreciated
    The vol con will be more likely to give you "0" volts (if there is not a fault) and more useful information.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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    Quote Originally Posted by killer76 View Post
    ... I was asked to see if you can you give a little more on the ground detectors - ...
    Code section is 2017 NEC 250.21.B Also suggest reading 250.21.A and 250.21.C.

    This is not a design. It is missing minor things like fuses.

    If 240V incandescent bulbs are not available, 240V transformered pilots also work.

    the worm
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    Without data you’re just another person with an opinion – Edwards Deming

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