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Thread: Floating neutral in CT cabinet

  1. #1
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    Floating neutral in CT cabinet

    I’m looking at an outdoor CT cabinet with a service disconnect located immediately adjacent to it.
    The water main is serving as the grounding electrode and the GEC runs from there back to the service disco.

    There are two ground rods acting as supplementary electrodes to the water main
    but they are tied to a ground lug bolted inside of the CT cabinet while the neutral bar inside the CT cab floats.

    Before the GEC from the ground rods lands at the CT ground lug it passes through grounding bushings that bond it’s parallel service raceways back to the service disconnect where the MBJ makes the enclosure/ neutral bond.

    My question is if the CT neutral is left to float, would the connection made between the ground rod GEC passing through the bonding bushings provide the bonding required by 250.53D2- specifically #3 on that list?

  2. #2
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    Quote Originally Posted by rojay View Post
    The water main is serving as the grounding electrode and the GEC runs from there back to the service disco.
    So far so good.

    There are two ground rods acting as supplementary electrodes to the water main
    but they are tied to a ground lug bolted inside of the CT cabinet while the neutral bar inside the CT cab floats.
    The rod GEC should land in the disco with the water GEC.
    The neutral in the CT cab should be bonded to the lug on the CT cab.

    Before the GEC from the ground rods lands at the CT ground lug it passes through grounding bushings that bond it’s parallel service raceways back to the service disconnect where the MBJ makes the enclosure/ neutral bond.
    The conductor from the bushings to the CT lug can remain if it's large enough.

    My question is if the CT neutral is left to float, would the connection made between the ground rod GEC passing through the bonding bushings provide the bonding required by 250.53D2- specifically #3 on that list?
    No, the neutral should be directly bonded to the CT cab lug in the CT cab.

    General rule: The EGC system starts at the service disco. Ahead of that, the neutral itself is used.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  3. #3
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    Quote Originally Posted by LarryFine View Post
    So far so good.


    The rod GEC should land in the disco with the water GEC.
    The neutral in the CT cab should be bonded to the lug on the CT cab.


    The conductor from the bushings to the CT lug can remain if it's large enough.


    No, the neutral should be directly bonded to the CT cab lug in the CT cab.

    General rule: The EGC system starts at the service disco. Ahead of that, the neutral itself is used.
    Larry, just a few disagreements

    IMO the rods GEC can land anywhere on the service conductors. It sounds like it is not compliant because it is spliced, non irreversibly, before it gets to the grounded conductor. To really nitpick, the code doesn't seem to support the idea of more than 1 GEC, but everyone does it.

    Also, IMO, it is possible for the CT cabinet to be "not directly" bonded to the neutral with a SSBJ or an approved raceway with proper service bonding. Not sure if the OP has that.....
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  4. #4
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    One of the major utilities in my area absolutely prohibits any connection between the neutral and the CT enclosure. You have to use a supply side bonding jumper to bond their CT cabinets.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  5. #5
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    Quote Originally Posted by don_resqcapt19 View Post
    One of the major utilities in my area absolutely prohibits any connection between the neutral and the CT enclosure. You have to use a supply side bonding jumper to bond their CT cabinets.
    I run into this as well. Kind of shame, as on a larger service with multiple raceways, if the CT can is far from from the disconnect this can get expensive for no good reason.

  6. #6
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    Basically, the crux of my original question was- would everything the way it’s currently tied together be code compliant without having to add or remove anything? Sounds like it’s a “no.”

    I agree it’s not an ideal setup by any means with grounding electrodes/conductors attached at the CT can AND the service disconnect but outside of the fact that the CT neutral floats how is this arrangement much different than what you see on an everyday residential service?
    The ground rods located at the meter ped outside tie to the water main GEC landed inside at the MCB panelboard by way of the service neutral.

    Since I don’t have a bonded neutral in my CT enclosure, I thought 250.53D3 would allow my supplemental electrode(s) to be bonded to a non flexible grounded service raceway. This is being done by connection to the grounding bushings. There are grounding bushings at both ends of the service raceway.

    Lastly, it is my understanding that everything that Larry mentioned about neutral bonding and routing all GEC’s to the service disconnect could equally apply to the CT cab- if there weren’t any POCO issues in doing so. Only the MBJ would need to be installed at the service disconnect.

  7. #7
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    Quote Originally Posted by don_resqcapt19 View Post
    One of the major utilities in my area absolutely prohibits any connection between the neutral and the CT enclosure. You have to use a supply side bonding jumper to bond their CT cabinets.
    Which kind of makes no sense, usually POCO's add bonding jumpers to things that maybe don't need them, yet prohibit it in this instance.

    Bottom line is CT cabinet is often on the POCO side of the "service point" and they can require anything they want there, even if it don't make sense to us.
    I live for today, I'm just a day behind.

  8. #8
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    Quote Originally Posted by kwired View Post
    Which kind of makes no sense, usually POCO's add bonding jumpers to things that maybe don't need them, yet prohibit it in this instance.

    Bottom line is CT cabinet is often on the POCO side of the "service point" and they can require anything they want there, even if it don't make sense to us.
    No matter where is it, in relation to the service point, the CT needs to have a bonding connection for safety.
    Don, Illinois
    (All code citations are 2017 unless otherwise noted)

  9. #9
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    Quote Originally Posted by don_resqcapt19 View Post
    No matter where is it, in relation to the service point, the CT needs to have a bonding connection for safety.
    I agree. NEC doesn't apply to POCO side. All the POCO's around here will want it bonded to the grounded conductor, and usually will make up all connections within the CT cabinet. Contractor may at times mount the cabinet and enter it with raceway's, and usually pull load side conductors, they may be required to run line side raceway but POCO's typically pull line side conductors. And you might find those conductors sized smaller than NEC would require them to be.
    I live for today, I'm just a day behind.

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