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Thread: 400 amp service grounding

  1. #1
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    400 amp service grounding

    I came across a 120/240 volt single phase 400 amp service at a residential job yesterday. It was a typical back to back installation with a 320 amp meter and two 2” RMC 90’s terminating at 2 separate 200 amp MB panel boards via 3-3/0 service entrance conductors.

    Along with the service entrance conductors in each raceway a supply side bonding jumper was pulled and terminated at bonding bushings at both ends of each raceway.

    While an NEC allowed parallel path for neutral current already exists between the meter can and the service disconnects via the 2” RGC’s - is the addition of another parallel path via #4 SSBJ’s pulled with the service conductors technically a code violation or just a waste of money?

  2. #2
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    Quote Originally Posted by rojay View Post
    I came across a 120/240 volt single phase 400 amp service at a residential job yesterday. It was a typical back to back installation with a 320 amp meter and two 2” RMC 90’s terminating at 2 separate 200 amp MB panel boards via 3-3/0 service entrance conductors.

    Along with the service entrance conductors in each raceway a supply side bonding jumper was pulled and terminated at bonding bushings at both ends of each raceway.

    While an NEC allowed parallel path for neutral current already exists between the meter can and the service disconnects via the 2” RGC’s - is the addition of another parallel path via #4 SSBJ’s pulled with the service conductors technically a code violation or just a waste of money?
    The rule on metal service raceways is you need more then just standard locknuts to assure the raceway is bonded. It only needs such bonding at one point.
    I live for today, I'm just a day behind.

  3. #3
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    Quote Originally Posted by kwired View Post
    The rule on metal service raceways is you need more then just standard locknuts to assure the raceway is bonded. It only needs such bonding at one point.
    So then the only time the NEC would require bonding at both ends of a service raceway would be in the case of concentric/eccentric ko’s at both ends?

  4. #4
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    Quote Originally Posted by rojay View Post
    So then the only time the NEC would require bonding at both ends of a service raceway would be in the case of concentric/eccentric ko’s at both ends?

    Nope, it's still only required at one end. You're are not trying to maintain the continuity between the two pieces of equipment you are only trying to ensure that the service raceway is bonded with a means better than standard locknuts.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  5. #5
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    Quote Originally Posted by rojay View Post
    So then the only time the NEC would require bonding at both ends of a service raceway would be in the case of concentric/eccentric ko’s at both ends?
    That only applies to metallic GEC conduits.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

  6. #6
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    Thanks for the clarification guys! Great point- the service raceway is no less bonded to the service equipment by using only one grounding bushing (w/ jumper if necessary) vs. using two.

  7. #7
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    Quote Originally Posted by rojay View Post
    So then the only time the NEC would require bonding at both ends of a service raceway would be in the case of concentric/eccentric ko’s at both ends?
    Quote Originally Posted by rojay View Post
    Thanks for the clarification guys! Great point- the service raceway is no less bonded to the service equipment by using only one grounding bushing (w/ jumper if necessary) vs. using two.
    Others answered your question, I will add the time you will need say a bonding bushing at both ends of a raceway is if using the raceway as an EGC and you have concentric/eccentric KO's at both ends and a requirement to bond around said KO's. This of course would be non service raceway for what I am describing.
    I live for today, I'm just a day behind.

  8. #8
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    Quote Originally Posted by kwired View Post
    Others answered your question, I will add the time you will need say a bonding bushing at both ends of a raceway is if using the raceway as an EGC and you have concentric/eccentric KO's at both ends and a requirement to bond around said KO's. This of course would be non service raceway for what I am describing.
    But what if things were arranged such that a service raceway was the sole fault path? Then I believe we would need a BB at both ends.
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

  9. #9
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    Quote Originally Posted by electrofelon View Post
    But what if things were arranged such that a service raceway was the sole fault path? Then I believe we would need a BB at both ends.
    Can you name a scenario where that would be possible? All of the equipment on the line side of the service disconnect should be bonded to the neutral and not really on the metal raceway for any return path. Same scenario with a PVC service raceway.
    Rob

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    All responses based on the 2014 NEC unless otherwise noted

  10. #10
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    Quote Originally Posted by infinity View Post
    Can you name a scenario where that would be possible? All of the equipment on the line side of the service disconnect should be bonded to the neutral and not really on the metal raceway for any return path. Same scenario with a PVC service raceway.
    Why can't I use an approved raceway as the fault path at a service? Bonding to the neutral is one option but I believe bonding jumpers or raceways are acceptable as well. Consider a metal pull box, them RGS raceway, then bonded panelboard. Couldn't the RGS bond the box?
    Ethan Brush - East West Electric. NY, WA. MA

    "You can't generalize"

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