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Thread: System not grounded

  1. #1
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    System not grounded

    System not grounded is the fault that has shown up on a a couple Pentek Intellidrives for my local pump installer. One I know is grounded. We wired it. 1PH in 3PH out. 120/240.

    Looking at the manuals explanation is of course, no ground, with the other being Line to Line voltage must be twice the line to ground voltage. How often does the drive check for this? Would a lightning transient be enough to trip the drive on this fault? He had two VFDs several miles apart trip with the same fault on the same day
    Tom
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  2. #2
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    How does the the VFD determine the system is ungrounded?
    Extremely unlikely.
    Tom
    TBLO

  3. #3
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    My take on it is that it is checking for symmetrical single phase voltage with respect to ground.
    Manual also mentions 3Φ feed in the symptoms, which would not be 2X voltage to ground. 1.732X not 2X, if fed from a 3Φ Y system
    Seems that a bad utility connection on the neutral or line could produce an unbalanced voltage, or a utility blip.
    Its probably hard on the inverter as designed, if there is an unbalance.

    MTW

  4. #4
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    does it reset and run fine (at least for undetermined amount of time)?

    If so maybe lightning transient is the cause.

    Well man in my area that installs Pentair drives provides a surge protector usually to be connected to the branch circuit device - says won't warranty the unit without it. True or not doesn't matter to me, I don't think it hurts to install it anyway plus if at the main panel kind of becomes a whole house protector anyway, what he is providing is basically a whole house type protector.
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  5. #5
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    These are both 1PH in with 3PH out so we should have the L-L twice the L-G. Typical single phase service from the POCO so an ungrounded system is highly unlikely.
    Tom
    TBLO

  6. #6
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    Quote Originally Posted by ptonsparky View Post
    System not grounded is the fault that has shown up on a a couple Pentek Intellidrives for my local pump installer. One I know is grounded. We wired it. 1PH in 3PH out. 120/240.

    Looking at the manuals explanation is of course, no ground, with the other being Line to Line voltage must be twice the line to ground voltage. How often does the drive check for this? Would a lightning transient be enough to trip the drive on this fault? He had two VFDs several miles apart trip with the same fault on the same day
    Yes, a lightning strike (or really, any high energy spike) could cause this. The line side of most VFDs is designed to be fed from a Wye system, and there are MOVs across the line side of the diode bridge to protect it. Those MOVs are referenced to ground in a wye pattern through a 4th MOV, then in some designs, they sense the presence of that ground connection through that 4th MOV. If a high energy surge hits the line side and that MOV vaporizes in the performance of its duty, the drive loses its ground reference and the line sensing system knows it, because the diode bridge is now exposed to the next hit and could fail (if it has not already). So this fault is made so that it cannot be reset automatically, forcing you to go look at it.

    When they don't give you these details in the manual, it's because they want you to call a service tech out. The MOVs and line sensing is usually together on a board and before just replacing it, there are other checks that should be made, such as a diode check of the bridge, capacitor checks etc., things that average Joes not familiar with VFDs might not be equipped to do.
    Last edited by Jraef; 06-13-18 at 10:59 AM.
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  7. #7
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    Quote Originally Posted by ptonsparky View Post
    These are both 1PH in with 3PH out so we should have the L-L twice the L-G. Typical single phase service from the POCO so an ungrounded system is highly unlikely.
    Not relevant in your applications but if connected to a 208/120 wye system could be an issue. But if you had three phase source you would think you would get a drive set up for three phase input also.
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  8. #8
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    VFDs I install (AB) all have ground fault protection.
    I install SPDs on every electrical service, typically one for the 480/277 and one on the 120/240. I install expensive instrumentation and since installing SPDs, have not seen issues with power supplies and circuit boards failing. Almost everything has a microprocessor...
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    2. You get what you pay for
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  9. #9
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    Quote Originally Posted by tom baker View Post
    VFDs I install (AB) all have ground fault protection.
    I install SPDs on every electrical service, typically one for the 480/277 and one on the 120/240. I install expensive instrumentation and since installing SPDs, have not seen issues with power supplies and circuit boards failing. Almost everything has a microprocessor...
    Rules for SPDs from Mike Holt
    1. More is better
    2. You get what you pay for
    What OP has isn't a general purpose drive, it is a unit containing a drive and customized specifically for use with submersible pump motors. Many typical drive parameters you see on a general purpose drive are not something that is user changeable. There are other parameters that are not typical on a general purpose drive and only apply to what this unit was designed for. The main part of it is a VFD but it is built for a specific application and for use with specific interconnecting components.

    Sorry I maybe misinterpreted what you said, but will leave the information here anyway as general information on what he has.
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  10. #10
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    Quote Originally Posted by tom baker View Post
    VFDs I install (AB) all have ground fault protection.
    I install SPDs on every electrical service, typically one for the 480/277 and one on the 120/240. I install expensive instrumentation and since installing SPDs, have not seen issues with power supplies and circuit boards failing. Almost everything has a microprocessor...
    Rules for SPDs from Mike Holt
    1. More is better
    2. You get what you pay for
    This was the other question the Pump Installer had.
    Thank you
    Tom
    TBLO

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