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Thread: 240volt Delta non grounded

  1. #1
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    240volt Delta non grounded

    I have a system 480v 3ph to 240v 3ph delta to delta transformer which has a voltage detector device on the secondary, which is detecting voltage on the grounded enclosure, which has people walking by concerned, but the grounded cabinet is grounded back to another voltage source, not the 240v source because it is not grounded at the transformer.

    The voltage between the grounded cabinet and the ground wire on the voltage detection device is 17volts, which is what is blinking the lights.
    The voltage phase to ground is 130v on 2 phases, 158 on the 3rd. But since there is no path back to the source, I don't know what that really means.
    I am told that it was installed that way on purpose, because grounding the circuit interfered with some testing of equipment.

    I have another identical system which is not blinking the ground indicator lights, but I can't tell what the difference is.
    I would prefer a grounded system, but that is not what I have.

    Thanks for any insight.

  2. #2
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    Quote Originally Posted by LarrywdH View Post
    I have a system 480v 3ph to 240v 3ph delta to delta transformer which has a voltage detector device on the secondary, which is detecting voltage on the grounded enclosure, which has people walking by concerned, but the grounded cabinet is grounded back to another voltage source, not the 240v source because it is not grounded at the transformer.

    The voltage between the grounded cabinet and the ground wire on the voltage detection device is 17volts, which is what is blinking the lights.
    The voltage phase to ground is 130v on 2 phases, 158 on the 3rd. But since there is no path back to the source, I don't know what that really means.
    I am told that it was installed that way on purpose, because grounding the circuit interfered with some testing of equipment.

    I have another identical system which is not blinking the ground indicator lights, but I can't tell what the difference is.
    I would prefer a grounded system, but that is not what I have.

    Thanks for any insight.
    The enclosure should not have any connection except capacitive to either the 480 source wires or the 240 output wires. The ungrounded 240 delta should be floating, tied by load capacitance only to a ground reference. If everything is balanced it should float with about 137 to ground on all three phase wires. There are only two ways that the enclosure could be raised to 17V above remote ground is the combination of two things:
    1. There is some unbalanced leakage from the output delta to the enclosure and at the same time the EGC connecting the enclosure ground to the remote ground source is no longer a solid connection, or
    2. There is some current (source unknown) being injected into the local earth so that the local earth ground electrode is at a 17V potential difference from the remote ground point.
    Either of these two situations needs to be corrected!

  3. #3
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    Golddigger

    "The enclosure should not have any connection except capacitive to either the 480 source wires"
    The cabinet is grounded through the supply conduit, and equipment grounds for other grounded circuits in the same enclosure, from a separate supply.

    "If everything is balanced it should float with about 137 to ground on all three phase wires"
    This is true on the other system I mentioned but not the one in question, I have 158v to ground on one phase.
    The 17volts I am getting is from the grounded enclosure to the ground wire on the voltage indicating device.


    https://www.graceport.com/cms/wp-con...es_it_work.pdf

    Thanks for the comment

  4. #4
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    Quote Originally Posted by LarrywdH View Post
    Can you test for bonding integrity, and remote injection current, or try a new sensor, then post your results.

    Quote Originally Posted by GoldDigger View Post
    1. There is some unbalanced leakage from the output delta to the enclosure and at the same time the EGC connecting the enclosure ground to the remote ground source is no longer a solid connection, or
    2. There is some current (source unknown) being injected into the local earth so that the local earth ground electrode is at a 17V potential difference from the remote ground point.
    Either of these two situations needs to be corrected!
    Roger Ramjet NoFixNoPay

  5. #5
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    Looking at the not quite complete information in the product brochure, it appears that the unit is sensing current from the floating wye point inside the device and its ground wire, not to any hypothetical connection to the enclosure.
    1. Measure from the actual enclosure (connected via conduit to remote ground) and the local ground terminal of the device. (What exactly is your ground reference?
    2. Measure between the local ground reference (if there is one) and the enclosure.

    It is not clear from your description so far whether there is indeed a voltage on the enclosure or just an offset of the ungrounded delta from the EGC connection. If the former, it needs to be fixed. If the latter, it suggests that either the transformer or the connected load equipment is not balanced in impedance between each phase and the enclosure. That may or may not indicate a more serious problem, but it does not indicate any immediate shock hazard.
    JMO

  6. #6
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    "Can you test for bonding integrity, and remote injection current, or try a new sensor, then post your results."
    The cabinet is supplied with 3 different voltage sources all with egc's and metal conduit that is installed and bonded.
    The 480v supply is right beside the 240v, and has an identical voltage detector device, and reads properly with no flickering ground indicators, when connected to the 480v supply. I swapped the connections for the 2 identical indicator devices between the 240v and 480v supplies and the problem followed the 240v supply not the device.
    I'm not familiar with "remote injection current".

    The supply transformer for the 240v system reads 240v phase to phase, and reads 128, 158, 131volts to ground at the transformer secondary with the main circuit breaker on the 240v panel open.

    "1. Measure from the actual enclosure (connected via conduit to remote ground) and the local ground terminal of the device. (What exactly is your ground reference?
    2. Measure between the local ground reference (if there is one) and the enclosure. "
    The ground wire from the voltage indicating device is normally connected to the grounding bus in the enclosure, when connected the ground lights flicker on the device.
    I disconnected this conductor and measured voltage from the conductor back to it's connection point on the grounding bus.
    I will measure from the enclosure to the local ground reference.

  7. #7
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    Just to make sure I'm clear this is a 240v 3 phase ungrounded system and there is another 240v 3 phase ungrounded system in the same room, from the same enclosure, fed from an identical 480v to 240v transformer, and the panels that are fed from the other 240v system are not causing the flickering ground indicator lights.
    Thanks for your time and expertise.

  8. #8
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    Seems to me you effectively eliminated remote injection currents, or a faulty indicator as causes.

    You may have also eliminated System bonding integrity as a cause.

    Turning off (isolating) each connected load may be next, but first consulting the indicator MFG, Customer Tech support might determine if 17volts really is problematic.
    Roger Ramjet NoFixNoPay

  9. #9
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    Thank you,
    I have been in consultation with the manufacturer's technical support, 10v or higher can cause dim flickering.

  10. #10
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    "Turning off (isolating) each connected load may be next"
    The 240v supply feeds numerous test points in a lab, all of those were not in use with nothing connected at the time when I was taking readings.
    The voltage to ground readings are what I think is causing the issue, but I don't know what is causing the readings to begin with.
    I did take readings at the transformer, with everything else isolated and still got the odd readings, 128, 158, 131v to ground.
    As stated earlier the readings should be 137v to ground on all three phases, and I have an identical set up right beside the one in question, that the readings are 137v to ground.
    Thanks

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