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Thread: When are grounding bushings required?

  1. #1
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    When are grounding bushings required?

    I'm trying to get a better grasp on when grounding bushings are required.

    I've read 250.92 and 250.97.

    You have to bond any metallic service entrance raceways. 250.92

    250 volts or more: You only have to bond raceways after the service if they terminate into concentrics or eccentrics that are not listed for bonding. 250.97.

    How about flex carrying 480 3-phase stubbing up from a PVC FA to a transformer? This would be after the service. The way I'm interpreting it is that it wouldn't require a grounding bushing.

    Say a grounding bushing is required on the service side, rigid conduit, no concentrics. Can you use one of these:

    http://www.aifittings.com/g_3.htm

  2. #2
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    Quote Originally Posted by wireman71
    How about flex carrying 480 3-phase stubbing up from a PVC FA to a transformer? This would be after the service. The way I'm interpreting it is that it wouldn't require a grounding bushing.
    No bonding bushing required assuming a punched KO.

  3. #3
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    "Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking."

  4. #4
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    Nice pics, did those come off a Mike Holt CD? Thanks!

  5. #5
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    Quote Originally Posted by wireman71
    Nice pics, did those come off a Mike Holt CD? Thanks!
    Hope they answered your questions... some of the graphics can be found at mike holts website.
    "Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking."

  6. #6
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    Thanks Stickboy...same pics from my Holt books....Yes at metallic service raceways at the line side.
    Greg

    Electrical Inspector in our Nations Capital

  7. #7
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    From the UL White Book - 2007



    Metal Outlet Boxes (QCIT)
    This category covers metallic flush device boxes, conduit bodies, conduit boxes, floor boxes, outlet boxes, special purpose boxes, extension rings, covers, and flush-device cover plates.


    CONCENTRIC OR ECCENTRIC KNOCKOUTS
    All boxes with concentric or eccentric knockouts have been investigated for bonding and are suitable for bonding without any additional bonding means around concentric (or eccentric) knockouts where used in circuits above or below 250 V, and may be marked as such.


    GROUNDING
    Clamps for armored cable, flexible metal conduit, metal-clad interlocking armor ground cable, metal-clad continuous smooth-sheath cable, or metal-clad continuous corrugated-sheath cable are considered suitable for grounding where installed in accordance with ANSI/NFPA 70, "National Electrical Code" (NEC).
    Instructor, Industry Advocate

  8. #8
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    Quote Originally Posted by stickboy1375
    Nice pics, but let's say that the meter pan is on top of the load center and has a panel hub for the nipple. Does nipple require a ground bushing boding it to the meter pan?
    My son is one of the Few, the Proud, the Infidel.
    Sgt. Mickey, 0311 USMC

  9. #9
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    Quote Originally Posted by Minuteman
    Nice pics, but let's say that the meter pan is on top of the load center and has a panel hub for the nipple. Does nipple require a ground bushing boding it to the meter pan?
    Check out 250.92 (B), I believe # 2 would meet the requirement. So no bushing required inside the meter pan.
    Last edited by stickboy1375; 03-09-08 at 03:23 PM.
    "Electricity is actually made up of extremely tiny particles called electrons, that you cannot see with the naked eye unless you have been drinking."

  10. #10
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    Quote Originally Posted by stickboy1375
    Check out 250.92 (B), I believe # 2 would meet the requirement. So no bushing required inside the meter pan.
    That's the way I read it, but it is a local unofficial thing to require a bonding bushing on ALL nipples that have unfused conductors.
    My son is one of the Few, the Proud, the Infidel.
    Sgt. Mickey, 0311 USMC

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