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Thread: Conduit Bonding

  1. #1

    Default Conduit Bonding

    I have an EMT conduit inside the house that goes to a pool building. Where it leaves the house, it transitions to PVC conduit. Inside this conduit is a 6-3 feeder with a #8 insulated equipment grounding conductor.

    The conduit is fastened to the subpanel from which it originates and is bonded there with a bonding bushing. Is there any requirement to additionally bond the last EMT piece where the transition to PVC occurs? If so, how do I do this?

    Bonding rules for conduit stubs seem kind of weird, and this may not be a stub since one end is connected to a panel. Continuous runs of bolted EMT can serve as a grounding path, and you must hope that a coupling doesn't come loose. But why must isolated sections be bonded at both ends? Or don't they have to be....
    Mark

  2. #2

    Default

    Emt must be bonded in different conditions in different ways.

    First you are changing from EMT grounidng path to a PVC conduit with an insulated groudning wire in that conduit.

    First concern is if this is a feeder you should be fine. IF this is a branch circuit to that pool underwater light then you are in err of minimum safety standard requiring a green grounding wire from panel to light non stop.

    Where you are transitioning from EMT to PVC with grounding wire then you need to use a junction box with a bonding bushing on the end of the EMT used as a grounding path. Then from the bonding bushing on the end of your EMT grounding path you would connect your green grounding wire installed into the PVC conduit to continue your grounding path.

    A bonding bushing normally is only required when a metal conduit is connected to a panel or box that still has knock out rings installed thus relying on those knock out rings as the grounding path. These knock out rings are not allowed to be use as a grounding path requiring a bonding bushing to make the jump across those knock out rings still being used as part of the metal box or panel.

    In some cases such as a metal conduit protecting a grounding electrode conductor going to a ground rod both ends of that conduit must be grounded. This is a special rule for grounding electrode conductors. This is why most people use PVC to protect grounding electrode conductors going to a grounding electrode.

    Then we have what is called main bonding jumpers for separately derived power sources and also equipment bonding jumpers connecting more than one metal to the other metal for continuous ensured grounding.

    WE could go on and on concerning different situations throughout the Code caling for and not calling for bond bushings and ensured grounding paths.

    Hope this clears the mud a little bit

    Wg

  3. #3

    Default

    This conduit is for a pool feeder and not a branch circuit. However, my preference was to run the grounding wire completely separately back to the panel (no splices). I don't want to use the EMT as a grounding path, but I know I have to bond it.

    Because I just coupled the EMT to PVC, there is no way to tie the grounding wire to the end of the EMT. Can I run a separate wire along the outside of the EMT to bond it at the end, or is my only choice to put in a J box and tie the ground wire to the box and use a bonding bushing on the EMT? Can I do without the bonding bushing if the hole is not a concentric knockout?
    Mark

  4. #4

    Default

    I see nothing in the NEC that requires a metal conduit to be bonded at each end unless that metal conduit is used as a grounding path or to protect a grounding electrode conductor connecting to a grounding electrode system. There is a rule requiring a metal conduit to be bonded but if not used in the manner mentioned above this metal conduit is not required to be bonded at each end.

    As I understand you are using it you are using a coupling to transcend from metal conduit to plastic conduit with no box and your conduit contains a grounding path with no plans to use that metal conduit as a grounding path. Connecting to the panel box without eccentrics at that panel will bond that conduit. No further bonding is required.

    Example of same principle is a UF cable protected from teh panel to where it goes under ground. A plastic bushing is required to ensure no abrasion but no further bonding is required.

    You are doing no different in your design other than running PVC the area outside and underground. No different. No further bonding is required the conduit is bonded already where it is connected at the source. Both ends are only required to be bonded if you installed a metal box at the end of that conduit. Then you would need a bonding jumper to bond both the metal conduit and the grounding wire to that metal box. If no box termination of that conduit no further bonding is required. Using a coupling to transcend from metal to plastic has no bonding concern on that far end of that metal conduit because it is not a complete conduit installation of metal conduit path. No different than running PVC the entire path from end to end.

    HOpe this helps

    Wg

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