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Thread: LFMC Bonding Bushing Concentric KOs

  1. #1
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    LFMC Bonding Bushing Concentric KOs

    Hello, I have read some old threads in the forum and am still a bit confused about the correct application of a bonding bushing when using LFMC (Not for service). Say, I have to run a LFMC between two enclosures (LFMC is not suitable for being used as an EGC per 250.118(6) ), the circuit is over 250V to ground, both two enclosures have concentric KOs not listed for grounding and bonding over 250V, a wire type EGC is pulled through the LFMC to bond the two enclosures. Do I still need to install a bonding bushing on at least one end? I am thinking Yes because the LFMC has metal and needs to be bonded to the enclosure on at least one end since the LFMC connector is not listed/suitable for bonding where KOs remain. But there seems to be a different opinion, since LFMC is not suitable to be used as an EGC, just like a PVC so no bonding bushing on either end is required.
    Any comments and opinions would be really appreciated!

  2. #2
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    IMO since you have concentric KO's on both ends one of them would need a bonding bushing to bond the raceway. In your example you cannot rely on the standard locknuts because of the two factors present, concentric KO's and the conductors are over 250 volts to ground.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  3. #3
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    Quote Originally Posted by infinity View Post
    IMO since you have concentric KO's on both ends one of them would need a bonding bushing to bond the raceway. In your example you cannot rely on the standard locknuts because of the two factors present, concentric KO's and the conductors are over 250 volts to ground.
    Given the use of a wire EGC, what code requires you to attach a bonding bushing to both ends as opposed to just one end, when ring KO's are on both ends? Dead-end bonding, vs parallel to the EGC bonding of the metal raceway.

    Also consider the case of a plastic enclosure, which obviously couldn't depend on standard locknuts to establish ground. Is there a difference between zero continuity of a plastic enclosure vs the metal ring KO's insufficient continuity, when determining if a raceway properly bonded on the other end needs a bonding bushing?

  4. #4
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    You're just bonding the flex. One grd. bushing should be enough.

  5. #5
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    Quote Originally Posted by Carultch View Post
    Given the use of a wire EGC, what code requires you to attach a bonding bushing to both ends as opposed to just one end, when ring KO's are on both ends? Dead-end bonding, vs parallel to the EGC bonding of the metal raceway.

    Also consider the case of a plastic enclosure, which obviously couldn't depend on standard locknuts to establish ground. Is there a difference between zero continuity of a plastic enclosure vs the metal ring KO's insufficient continuity, when determining if a raceway properly bonded on the other end needs a bonding bushing?

    I think that you misread my post. You only need to install a bonding bushing on one end. I stated about the concentric KO's on both ends and a bonding bushing on one end.

    Quote Originally Posted by infinity View Post
    IMO since you have concentric KO's on both ends one of them would need a bonding bushing to bond the raceway. In your example you cannot rely on the standard locknuts because of the two factors present, concentric KO's and the conductors are over 250 volts to ground.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  6. #6
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    Quote Originally Posted by Carultch View Post
    Given the use of a wire EGC, what code requires you to attach a bonding bushing to both ends as opposed to just one end, when ring KO's are on both ends? Dead-end bonding, vs parallel to the EGC bonding of the metal raceway.

    Also consider the case of a plastic enclosure, which obviously couldn't depend on standard locknuts to establish ground. Is there a difference between zero continuity of a plastic enclosure vs the metal ring KO's insufficient continuity, when determining if a raceway properly bonded on the other end needs a bonding bushing?
    Are you also saying bonding bushing has to be installed on one end to ensure LFMC is properly bonded at the knockout?

  7. #7
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    Quote Originally Posted by hill900505 View Post
    Are you also saying bonding bushing has to be installed on one end to ensure LFMC is properly bonded at the knockout?
    Yes. All metal raceways need to be properly bonded on at least one side, even if a wire EGC is present. If a wire EGC is present, the raceway just needs one side properly bonded. If the raceway is the EGC, both sides need proper bonding. The special cases are GEC raceways and service conductor raceways. GEC metal raceways require bonding bushings on both sides, service metal raceways require a bonding bushing on at least one side (even if standard locknuts get you the needed continuity, had it been a feeder raceway).

    Over 250V to ground and ring KO's remaining of either shape, and that connection is not proper continuity, unless the enclosure is listed otherwise. Some enclosures with KO's are listed otherwise, and opening the KO is significantly more difficult than a standard ring KO on an enclosure.

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