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Thread: Choosing a grounding system for a UPS... not sure which to go with?

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    Choosing a grounding system for a UPS... not sure which to go with?

    I'm spec'ing out a UPS. It's in a nonclassified area, 480V and 50KVA. I can choose either a high resistance ground or a solid ground... What factors should I consider in making this decision?

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    A high resistance ground is used where you want continuity of power with an alarm on a line to ground
    Solid ground system will open the OCPD on a line to ground or line to line.
    Its really a design decision, but with a HRG you need a ground detector and you probably knew that.
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    Quote Originally Posted by tom baker View Post
    A high resistance ground is used where you want continuity of power with an alarm on a line to ground
    Solid ground system will open the OCPD on a line to ground or line to line.
    Its really a design decision, but with a HRG you need a ground detector and you probably knew that.
    By ground detector, do you mean a GFCT?

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    Quote Originally Posted by jucesanc View Post
    I'm spec'ing out a UPS. It's in a nonclassified area, 480V and 50KVA. I can choose either a high resistance ground or a solid ground... What factors should I consider in making this decision?
    If you are using the UPS to supply standard receptacles, then I'm wondering if the NEC allows a HRG, or if it has to be a regular grounded system, like most normal receptacles would usually have.

    Personally, I have never seen a HRG UPS.

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    Would be highly unusual (and confusing for maintenance) to install HRG in a typ UPS installation. Especially such a small kva. Safety is key. Choose a solidly grounded system. You already have uninterruptible power as long as your DC source has capacity. Properly coordinate your breakers for higher reliability.

    If you have an external bypass, you have even more considerations to make.

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    Quote Originally Posted by jucesanc View Post
    I'm spec'ing out a UPS. It's in a nonclassified area, 480V and 50KVA. I can choose either a high resistance ground or a solid ground... What factors should I consider in making this decision?
    Is there a concern for high fault currents?

    Does the UPS have an integral transformer?

    If not, a solidly grounded system is more than sufficient in offering protection.

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    Quote Originally Posted by steve66 View Post
    If you are using the UPS to supply standard receptacles, then I'm wondering if the NEC allows a HRG, or if it has to be a regular grounded system, like most normal receptacles would usually have.

    Personally, I have never seen a HRG UPS.
    The UPS is supplying three 9 kva transformers for subpanels, and 10+ motorized valves.

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    Quote Originally Posted by jucesanc View Post
    By ground detector, do you mean a GFCT?
    No like this
    https://s21.q4cdn.com/920789611/file...ding-Panel.pdf
    Moderator-Washington State
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    Quote Originally Posted by tom baker View Post
    Seems like this option is intended to be connected ahead of all downstream equipment and wiring, but such equipment and wiring can be specified to handle fault currents. Would it be easier to use a solidly grounded system and have all equipment and wiring rated for the available fault current?

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